Iron-mediated allylic substitution reactions with chirality transfer. Stereochemistry of the formation of diastereo- and enantiomerically enriched olefinic and allylic tetracarbonyl iron complexes

Article abstract of DOI:10.1021/om010343l

(E)-Configurated allylic ligands (S)-6a-f and (S)-8, bearing a leaving group at C(3) (allylic position) and an electron acceptor substituent at C(1), were synthesized from enantiopure (S)-ethyl lactate [(S)-1]. Complexation with Fe₂(CO)₉

Full text of DOI:10.1021/om010343l

4312
Organometallics 2001, 20, 4312-4332
Ir on -Med ia ted Allylic Su bstitu tion Rea ction s w ith
Ch ir a lity Tr a n sfer . Ster eoch em istr y of th e F or m a tion of
Dia ster eo- a n d En a n tiom er ica lly En r ich ed Olefin ic a n d
Allylic Tetr a ca r bon yl Ir on Com p lexes
Dieter Enders,* Bernd J andeleit,*,† Stefan von Berg,§ Gerhard Raabe, and
J an Runsink
Institut fu¨r Organische Chemie der Rheinisch-Westfa¨lischen Technischen Hochschule,
Professor-Pirlet Strasse 1, D-52074 Aachen, Germany
Received April 26, 2001
(E)-Configurated allylic ligands (S)-6a -f and (S)-8, bearing a leaving group at C(3) (allylic
position) and an electron acceptor substituent at C(1), were synthesized from enantiopure
(S)-ethyl lactate [(S)-1]. Complexation with Fe2(CO)9 (13) afforded diastereomeric mixtures
of their (η2-alkene)tetracarbonyliron(0) complexes 14a ′/a ′′-f′/f′′ (acceptor group, Acc ) SO2-
Ph) and 15′/′′ (Acc ) CO2Me) (48% - quant.; de < 3-70%), each diastereomer in enantiopure
form (Note: descriptors ′ and ′′ denote major and minor diastereomer). Synthetically useful
results were obtained for allylic ligands bearing a benzylic protecting group [(S)-6a and (S)-
8] and using hexane or diethyl ether as solvent (14a ′/a ′′: quant., de ) 70%; 15′/′′: 75-88%,
de ) 10-16%). Complexes 14a ′/a ′′ were fractionally crystallized, and their molecular
structures were determined by X-ray diffraction, allowing for an assignment of the absolute
configurations of complexes 14a ′/a ′′-f′/f′′ and 15′/′′. “W”-shaped complexes 14a ′, 15′′ (Ψ-
exo-14,15) were expected to yield syn-Me,syn-Acc-configured and “S”-shaped complexes 14a ′′,
15′ (Ψ-endo-14,15) accordingly anti-Me,syn-Acc-configured cationic complexes 18 and 19 upon
treatment with HBF4. Complex 14a ′ (de ) ee > 99%) reacted quantitatively to the syn-Me-
substituted (η3-allyl)tetracarbonyliron(1+) complex 18′ (syn-Me,syn-SO2Ph-18) (syn-Me/anti-
Me > 99:1, ee > 99%). Diastereomeric mixtures of complexes 14a ′/a ′′ gave mixtures of
complexes 18′, 18′′ (anti-Me,syn-SO2Ph-18) and ent-18′′ (ent-syn-Me,syn-SO2Ph-18). Conver-
sion of complex 14a ′′ to 18′′ or complex 18′′ itself was subjected to an anti-Me f syn-Me
isomerization process, yielding eventually a diastereomeric mixture of complexes 18′′ and
ent-18′′, thus lowering the overall enantiomeric purity of syn-Me,syn-SO2Ph-substituted
complexes 18. Conversion of a mixture of 15′/′′ (de ) 10%) to cationic complexes 19′/′′ did
not exhibit significant anti-Me f syn-Me isomerization (syn-Me:anti-Me ) 1:1.19, ee > 96%
for both diastereomers). Nucleophilic anti-addition of silyl enol ether 20 to complex 18′ or
silyl ketene acetal 21 to a complex mixture 19′/′′ afforded enantiopure alkenyl sulfone (R)-
23 or ester (S)-24 (82% - quant., ee >96 to >99%). Addition to a complex mixture containing
18′, 18′′, and ent-18′ yielded 23, albeit with lower enantiomeric purity (ee ) 59-66%). The
chirality transfer process of the iron-mediated allylic substitution proceeds with overall
retention (double inversion) of stereochemistry with respect to the stereogenic center of the
starting materials, conservation of (E)-double bond geometry, and complete γ-regioselectivity
for the nucleophilic addition reactions. Differences of configurative stability of the anti-
configured Me groups in the cationic π-allyl complexes 18′′ and 19′ were found requiring
appropriate consideration if used in stereocontrolled organic synthesis.
In tr od u ction
allyl complexes include Ni,5 Ru,6 Rh,7 Ir,8 Mo,9 W,10
Cu,11 Mn,12 Pt,13 Fe,14 Co,15 or Re atoms.16 Generally,
η3-allyl transition metal complexes can function as
Among the various carbon-carbon and carbon-
heteroatom bond forming reactions catalyzed or pro-
moted by transition metals,1-3 π-allyl transition metal
complexes have been recognized as versatile allylating
reagents in organic synthesis, with η3-allyl complexes
of palladium being the most frequently and intensively
studied species.4 Other important transition metal η3-
(1) General references for the use of transition metals and organo-
metallics in organic synthesis: (a) Tsuji, J . Transition Metal Reagents
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* Corresponding authors. E-mail for D.E.: Enders@RWTH-Aachen.de.
† New address: XenoPort, Inc., 2631 Hanover St., Palo Alto, CA
94304.
Organometallic Chemistry of the Transition Metals, 2nd ed.; J ohn Wiley
& Sons: New York, 1994. (f) Elschenbroich, C.; Salzer, A. Organome-
tallics; Wiley-VCH: Weinheim, 1992. (g) Harrington, P. J . Transition
Metals in Total Synthesis; J ohn Wiley & Sons: New York, 1990.
§ New address: Astra Zeneca R&D, 15185 So¨derta¨lje, Sweden.
10.1021/om010343l CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/11/2001

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4313
either electrophilic or nucleophilic allylating agents,
depending on the properties of the transition metal and
the coordinated ligand.
Cationic metal π-complexes of polyenic ligands have
received considerable attention as useful carbocation
equivalents stabilized by coordination to a transition
metal-ligand moiety and which possess an enhanced
reactivity toward a multitude of carbon and heteroatom
nucleophiles.17 Nucleophilic addition reactions are gen-
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ligand fragment, while regiochemical outcomes are most
often controlled by substitution pattern, the nature of
substituents, or both. Transition metal π-complexes of
unsymmetrically substituted ligands in which an achiral
metal-ligand fragment distinguishes the two enan-
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their enantiomerically pure form they are of significance
as valuable building blocks for the regio- and stereo-
controlled synthesis of organic target molecules. Orga-
noiron complexes are often employed stoichiometrically
and frequently display excellent regio- and stereocon-
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bonyliron(0), or (η5-cyclohexadienyl)tricarbonyliron(1+)
complexes have become useful reagents with widespread
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4314 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
Our group,21 and groups of Green,22 Speckamp,23 and
J ackson,24 demonstrated that nucleophilic addition to
cationic tetracarbonyl(η3-allyl)iron complexes substi-
tuted with electron-withdrawing functionalities on the
allyl moiety such as SO2Ph, CO2R, and CONR2 groups
proceeds with complete γ-regioselectivity with respect
to the electron acceptor group.
In addition, Nakanishi and co-workers reported the
synthesis of nonracemic, electron acceptor substituted,
neutral dicarbonylnitrosyl(η3-allyl)iron complexes useful
in regio- and enantioselective allylic amination reac-
tions.25 The utility of Ley’s (π-allyl)tricarbonyliron lac-
tone and lactame complexes, respectively, for 1,5 or 1,7
remote asymmetric induction has been illustrated ex-
tensively in recent years.26
thesis of highly enantiomerically enriched organic com-
pounds led to the development of several concepts.27 As
the most versatile concept, the “chirality transfer” or
“self-reproduction of chirality” approach involves dias-
tereoselective complexations of enantiopure (E)-con-
figured acceptor-substituted olefins to yield diastereo-
merically enriched (η2-alkene)Fe(CO)4(0) complexes
(Figure 1).28,29 The corresponding planar chiral (η3-allyl)-
Fe(CO)4(1+) complexes can be obtained in virtually
diastereo- and enantiomerically pure form. They rep-
resent synthetic equivalents of chiral a4-synthons A,
which are useful for “Umpolung” (reversed reactivity)
of classical d4-chemistry.30 Nucleophilic addition and
subsequent demetalation leads to the corresponding
allylic substitution products. The overall stereochemical
outcome of the “chirality transfer” process was unam-
biguously verified by the synthesis of various natural
products in their absolute configurations21d-f,i and by
X-ray determination of the molecular structure of some
addition products.31
In this article we wish to disclose a comprehensive
synthetic, mechanistic, and stereochemical study to
elucidate the stereochemistry of the formation of dia-
stereo- and enantiomerically enriched olefinic and allylic
tetracarbonyl iron complexes involved in our iron-
mediated allylic substitution process with chirality
transfer. The effect of various reaction parameters such
as different leaving groups, solvent polarity, and tem-
perature and their influence on the overall stereochem-
istry will be discussed. The determination of the mo-
lecular structure of various important intermediates will
be presented. A proposal of how the chirality informa-
tion is conserved and transferred in all of the different
steps during formation and reaction of olefinic and
allylic tetracarbonyl iron complexes based on the results
obtained will be given.
Our efforts to develop a synthetically useful iron-
mediated allylic substitution methodology for the syn-
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Dissertation, University of Technology Aachen, 1990. (l) Fey, P.
Dissertation, University of Bonn, 1985.
Resu lts a n d Discu ssion
Syn th esis of En a n tiop u r e (E)-Con figu r ed Accep -
tor -Su bstitu ted Alk en es 6 a n d 8. For our study, we
focused on (E)-configured electron acceptor substituted
alkene ligands of type (S)-6, which in turn were derived
from (-)-(S)-ethyl lactate [(S)-1] as the enantiopure
(26) (a) Ley, S. V.; Cox, L. R.; Middleton, B.; Worrall, J . M.
Tetrahedron 1999, 55, 3515. (b) Cox, L. R.; Ley, S. V. Chem. Soc. Rev.
1998, 27, 301. (c) Ley, S. V.; Cox, L. R.; Worrall, J . M. J . Chem. Soc.,
Perkin Trans. 1 1998, 3349. (d) Ley, S. V.; Middleton, B. Chem.
Commun. 1998, 1995. (e) Cox, L. R.; Ley, S. V. J . Chem. Soc., Chem.
Commun. 1998, 1339. (f) Ley, S. V.; Burckhardt, S.; Cox, L. R.; Worrall,
J . M. J . Chem. Soc., Chem. Commun. 1998, 229. (g) Ley, S. V.; Cox, L.
R. J . Chem. Soc., Chem. Commun. 1998, 227. (h) Ley, S. V.; Cox, L.
R.; Meek, G. Chem. Rev. 1996, 96, 423.
(27) (a) Enders, D.; J andeleit, B.; von Berg, S. In Organic Synthesis
via Organometallics, OSM V; Helmchen, G., Dibo, J ., Flubacher, D.,
Wiese, B., Eds.; Vieweg: Braunschweig, 1997; p 279. (b) Enders, D.;
J andeleit, B.; von Berg, S. Synlett 1997, 421.
(28) Review about chemical processses involving self-reproduction
of chirality: Seebach, D.; Sting, A. R.; Hoffmann, M. Angew. Chem.
1996, 108, 2880; Angew. Chem. Int. Ed. Engl. 1996, 35, 2708.
(29) Recent examples of applications of palladium metal catalysis
in chirality transfer reactions: (a) Doi, T, Yanagisawa, M, Miyazawa,
Yamamoto, K., Tetrahedron: Asymmetry 1995, 6, 389. (b) Suginome,
M.; Iwanami, T.; Matsumoto, A.; Ito, Y. Tetrahedron: Asymmetry 1997,
8, 859. (c) Michelet, V.; Geneˆt, J .-P. Bull. Soc. Chim. Fr. 1996, 133,
881. For other transition metal catalyzed chirality transfer reactions,
see for example refs 6-8, 14.
(22) (a) Charlton, M. A.; Green, J . R. Can. J . Chem. 1997, 75, 965.
(b) Zhou, T.; Green, J . R. Tetrahedron Lett. 1993, 34, 4497. (c) Gadja,
C.; Green, J . R. Synlett 1992, 973. (d) Green, J . R.; Carrol, M. K.
Tetrahedron Lett. 1991, 32, 1141.
(23) (a) de Koning, H.; Hiemstra, H.; Moolenaar, M. J .; Speckamp,
W. N. Eur. J . Org. Chem. 1998, 1729. (b) Speckamp, W. N. Pure Appl.
Chem. 1996, 68, 695. (c) Goubitz, G.; Selje´e, F. R.; Schenk, H.; Hopman,
J . C. P.; Hiemstra, H. Z. Kristallogr. 1996, 211, 714. (d) Goubitz, G.;
Selje´e, F. R.; Koot. W.-J .; Hiemstra, H. Z. Kristallogr. 1996, 211, 711.
(e) Koot, W.-J . Dissertation, University of Amsterdam, 1993. (f)
Hopman, J . C. P.; Hiemstra, H.; Speckamp, W. N. J . Chem. Soc., Chem.
Commun. 1995, 617. (g) Hopman, J . C. P.; Hiemstra, H.; Speckamp,
W. N. J . Chem. Soc., Chem. Commun. 1995, 619. (h) Koot, W.-J .;
Hiemstra, H.; Speckamp, W. N. J . Chem. Soc., Chem. Commun. 1993,
156.
(24) J ackson, R. W. F.; Turner, D.; Block, M. H. Synlett 1997, 789.
(25) (a) Nakanishi, S.; Okamoto, K.; Yamagushi, H.; Takata, T.
Synthesis 1998, 1735. (b) Nakanishi, S.; Memita, S.; Takata, T.; Itoh,
K. Bull. Chem. Soc. J pn. 1998, 71, 403. (c) Yamaguchi, H.; Nakanishi,
S.; Takata, T. J . Organomet. Chem. 1998, 554, 167. (d) Yamaguchi,
H.; Nakanishi, S.; Okamoto, K.; Takata, T. Synlett 1997, 722. (e)
Nakanishi, S.; Takata, T. Rev. Heteroat. Chem. 1997, 17, 153. (f)
Nakanishi, S.; Yamaguchi, H.; Okamoto, K.; Takata, T. Tetrahedron:
Asymmetry 1996, 7, 2219. (g) Itoh, K.; Otsuji, Y.; Nakanishi, S.
Tetrahedron Lett. 1995, 36, 5211.
(30) Seebach, D. Angew. Chem. 1979, 91, 259; Angew. Chem., Int.
Ed. Engl. 1979, 18, 239. (b) Hase, T. A. Umpoled Synthons; J ohn Wiley
& Sons: New York, 1987.
(31) Enders, D.; J andeleit, B.; Raabe, G. University of Technology
Aachen, 1995, unpublished results.

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4315
F igu r e 1. Principle of the “chirality transfer” or “self-reproduction of chirality” approach in our iron-mediated allylic
substitution reaction. Diastereoselective complexation of enantiopure (E)-configured acceptor-substituted alkenes yields
intermediate (η2-alkene)tetracarbonyliron(0) complexes. The corresponding enantiomerically enriched planar chiral (η3-
allyl) tetracarbonyliron(1+) complexes react in a regio- and face selective fashion with various nucleophiles to highly
enantiomerically enriched allylic substitution products of defined stereochemistry. The entire reaction cycle is supposed
to proceed with overall conservation of chirality information from central to planar back to central chirality.
chiral precursor (Schemes 1a-c) (Acc ) SO2Ph, CO2-
Me). Ester (S)-1 was converted in good yields (66-95%)
into the O-protected ethyl lactate derivatives (S)-3a -c
following appropriate standard OH group protection
protocols (Scheme 1a).32 (For specific reagents, condi-
tions, and yields see captions of Scheme 1.) The bulky
2-(methylene)naphthalene protecting group was intro-
duced in a two-step procedure via the amide (S)-2,32b
followed by standard Williamson etherification of (S)-2
to give the O-protected amide (S)-3d (Scheme 1a).
The O-protected R-hydroxy esters (S)-3a -c were
reduced with DIBAH to yield the corresponding alde-
hydes (S)-4a -c (89-98%) (Scheme 1a). Amide (S)-3d
gave after reduction with Red-Al aldehyde (S)-4d (58%)
(Scheme 1a).32b The enantiomeric excesses of the alde-
hydes (S)-4a -d were indirectly determined by 1H NMR
and 13C NMR spectroscopy after conversion to their
corresponding diastereomerically pure SAMP-hydra-
zones with the chiral enantiopure auxiliary SAMP [(-)-
(S)-1-amino-2-methoxymethyl)pyrrolidine].33 Compari-
son with appropriate epimeric mixtures of SAMP-
hydrazones from racemic aldehydes rac-4a -d showed
that both the O-protection and the reduction steps
proceeded virtually without racemization [(S)-4a -d : ee
> 98%]. Aldehydes (S)-4a -d were subjected to a modi-
fied Horner-Wadsworth-Emmons olefination proce-
dure with the phenylsulfonyl-substituted phosphonate
5 to yield alkenes (S)-6a -d (72-90%) (Scheme 1a).34,35
The methoxycarbonyl-substituted alkene (S)-8 was ob-
tained from aldehyde (S)-4a with methyl diethylphospho-
noacetate (7) (86%).34,36,37 Acidic cleavage of the TBDMS
protecting group of compound (S)-6c yielded alkenyl
sulfone (S)-6e in quantitative yield.32a,38 Acylation of
compound (S)-6e to (S)-6f (49%) was performed under
standard conditions (Scheme 1c).32a,39 The 1H NMR
spectra of purified compounds (S)-6a -f and (S)-8 dis-
3
played typical coupling constants J trans of ca. 15 Hz.
The enantiomeric excesses of compounds (S)-6a -f and
(S)-8 were determined by HPLC employing chiral
stationary phases. Comparison of racemic material rac-
6a -f and rac-8 with compounds (S)-6a -f and (S)-8
showed that no significant racemization occurred [(S)-
6a -f, (S)-8: ee > 99%].
Tet r a ca r b on yl(η2-a lk en e)ir on (0)
Com p lexes:
Ster eoch em ica l Con sid er a tion s. Previous results
from Speckamp et al. showed that a uniform configu-
ration of the carbon atom bearing the leaving group (and
the nature of the N-protecting group) was essential for
controlling the absolute stereochemistry and the result-
(34) (a) Blanchette, M. A.; Choy, W.; Davis, J . T.; Essenfeld, M. P.;
Masamune, S.; Roush, W. R. Tetrahedron Lett. 1984, 25, 2183. (b)
Rathke, M. W.; Novak, M. J . Org. Chem. 1985, 50, 2624. (c) Enders,
D.; von Berg, S.; J andeleit, B.; Org. Synth. 2001, 78, 177.
(35) (a) Shahak, I.; Almog. Synthesis 1969, 170. (b) Shahak, I.;
Almog. Synthesis 1970, 145. (c) Lee, J . W.; Oh, D. Y. Synth. Commun.
1990, 20, 273. (d) Lee, J . W.; Oh, D. Y. Synth. Commun. 1989, 19,
2209. (e) Enders, D.; von Berg, S. J andeleit, B. Org. Synth. 2001, 78,
169.
(36) Lombardo, L.; Taylor, R. J . K. Synthesis 1978, 131.
(37) Alkene (S)-8 is commercially available from ACROS Chimica,
Belgium. Enders, D.; J andeleit, B. ACROS Org. Acta 1995, 1, 59.
(38) (a) Hanessian, S.; Lavelee, P. Can. J . Chem. 1977, 55, 562. (b)
Hanessian, S.; Lavelee, P. Can. J . Chem. 1975, 53, 2975.
(39) Ho¨fle, G.; Steglich, W.; Vorbru¨ggen, H. Angew. Chem. 1978,
90, 602; Angew. Chem., Int. Ed. Engl. 1978, 17, 569.
(32) (a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; J ohn Wiley & Sons: New York, 1999. (b) Ito, Y.;
Kobayshi, Y.; Kawabata, T.; Takase, M.; Terashima, S. Tetrahedron
1989, 45, 5767. (c) Banfi, L.; Bernardi, A.; Colombo, L.; Gennari, C.;
Scolastico, C. J . Org. Chem. 1984, 49, 3784. (d) Corey, E. J .; Ven-
kateswarlu, A. J . Am. Chem. Soc. 1972, 94, 6190.
(33) Enders, D.; Klatt, M. In Encyclopedia of Reagents for Organic
Synthesis; Paquette, L. A., Ed., J ohn Wiley & Sons: New York, 1995;
Vol. 1, p 178.

4316 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
Sch em e 2. Syn th esis of Tetr a ca r bon ylir on (0)
Sch em e 1. Syn th esis of th e Alk en es (S)-6a -f a n d
(S)-8a
N-P r otected -5-(R)-isop r op oxy-3-p yr r olin -2-on es
cis-12 a n d tr a n s-1223 a
a
Reagents and conditions: (a) 2.0 equiv of [Fe2(CO)9] (13),
benzene, or Et2O, room temp, 18 h.
ing diastereomeric ratio during the complexation of
N-protected 5-(R)-isopropoxy-3-pyrrolin-2-ones (R)-11 to
give tetracarbonyl(η2-alkene)iron(0) complexes cis- and
trans-12 (Scheme 2).23
We hypothesized first that the leaving group unit
(OPG) in ligands (S)-6a -f and (S)-8 may effectively
differentiate the diastereotopic half rooms defined by
the plane through the double bond, and, second, that it
controls as well the approach of the coordinatively
unsaturated Fe(CO)4 moiety through a precoordination
mode (Figure 2).21 Complexation of unsymmetrically
substituted olefins of type (S)-6a -f and (S)-8 bearing a
stereogenic center at the allylic position results in the
formation of a mixture of diastereomers A and B in
which the metal-ligand fragment distinguishes be-
tween the two diastereotopic faces defined through the
plane of the olefinic bond. It can be proposed that steric
hindrance of both the leaving group unit and the iron
tetracarbonyl fragment in B results in a favored con-
formation of the single bond and leads to the less
strained conformer C (Figure 2). The structure of the
backbone of structure A, counting from the acceptor
functionality to the terminal methyl group, can be
regarded as “W”-shaped, whereas the same fragment
in C can be regarded as “S”-shaped (S t sickle).
According to a nomenclature introduced by Lillya et al.
for related tricarbonyl(η4-diene)iron(0) complexes, dia-
stereomer A can be assigned the Ψ-exo isomer (leaving
group unit directed exo or anti relative to the tetracar-
bonyliron moiety, structure D) and diastereomer C is
assigned the Ψ-endo isomer (leaving group unit directed
endo or syn relative to the tetracarbonyliron moiety,
structure E).40 Regarding the metal fragment-carbon
double bond binding mode as a “ferracyclopropane”
substructure (structures F and G), the newly generated
stereogenic centers (indicated with *) are in an inverted
stereochemical relationship to each other, although F
and G possess still identical stereochemistry at the
allylic position. C(1) denotes the R-carbon atom of the
complexed double bond next to the acceptor functional-
ity, C(2) the â-position, and C(3) the carbinol atom in
the γ-position.
a
Reagents and conditions: (a) 1.0 equiv of (S)-1, 1.3 equiv
of pyrrolidine, neat, room temp, 3 days (84%); (b) 1.0 equiv of
(S)-1, 2.0 equiv of Cl3C(CdNH)OBn, cat. TfOH, cyclohexane/
CH2Cl2 (7:1), room temp, 5 days (95%); (c) 1.0 equiv of (S)-1,
1.25 equiv of BomCl, 1.5 equiv of i-Pr2EtN, CH2Cl2, 0 °C to
room temp, 16 h (78%); (d) 1.0 equiv of (S)-1, 1.2 equiv of
TBDMSCl, 1.5 equiv of imidazole, DMF, 0 °C to room temp, 6
h (87%); (e) 1.0 equiv of (S)-2, 1.1 equiv of NaH (3 × washed
with n-hexane), 1.1 equiv of 2-(bromomethyl)naphthalene,
THF/DMF (3:1), 0 °C to room temp, 12 h (79%); (f) 1.0 equiv
of (S)-3a -c, 1.4 equiv of DIBAH in hexane, Et2O, -78 °C, 2 h,
then H+ (89-98%); (g) 1.0 equiv of (S)-3d , 0.6 equiv of Red-
Al, toluene, -10 °C, 2 h, then H+ (58%); (h) 1.0 equiv of (S)-
3a -d , 1.0 equiv of (EtO)2(PdO)CH2SO2Ph (5), 1.2 equiv of
LiBr, 1.1 equiv of Et3N, acetonitrile, 0 °C to room temp, 12 h
(72-90%); (i) 1.0 equiv of (S)-3a , 1.0 equiv of (EtO)2(PdO)CH2-
CO2Me (7), 1.2 equiv of LiBr, 1.1 equiv of Et3N, acetonitrile, 0
°C to room temp, 12 h (86%); (j) 1.0 equiv of (S)-6c, 3% HCl in
MeOH, 50 °C, 4 h (quant.); (k) 1.0 equiv of (S)-6e, 2.0 equiv of
AcCl, 2.0 equiv of Et3N, cat. DMAP, CH2Cl2, room temp 12 h
(49%). Abbreviations: PG: protecting group, TfOH: trifluo-
romethane sulfonic acid (F3CSO3H), BomCl: benzyl chloro-
methyl ether (BnOCH2Cl), TBDMSCl: tert-butyldimethylsilyl
chloride (t-BuMe2SiCl), DIBAH: diisobutylaluminum hydride
(i-Bu2AlH), Red-Al: sodium bis(2-methoxyethoxy)aluminum
hydride {Na[Al(OCH2CH2OMe)2H2]}, DMAP: 4-N,N-(dimethyl-
amino)pyridine.
(40) Clinton, N. A.; Lillya, C. P. J . Am. Chem. Soc. 1970, 92, 3058.

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4317
F igu r e 2. Working hypothesis: Complexation of the double bond of (E)-configured alkenes of type (S)-6a -f/(S)-8 by an
Fe(CO)4 unit leads to the formation of two possible diastereomers (structures A and B). Structure C presents a less strained
conformer of structure B. A Newman projection of the diastereomeric complexes (structures D and E) allows a relative
stereochemical assignment according to Lillya’s Ψ-exo/Ψ-endo nomenclature.40 A partial “ferracyclopropane structure”
(structures F and G) allows designation of absolute stereochemical descriptors. C(1) designates the R-carbon atom next to
the acceptor functionality, and C(2) the â-position (see text for details). Cahn-Ingold-Prelog (CIP) priority: Acc > C(1)
> C(2). Abbreviations: Acc: acceptor group.
Sch em e 3. Syn th esis of
(η2-Alk en e)tetr a ca r bon ylir on (0) Com p lexes
14a -f a n d 15a
suspended reactants were almost dissolved to form a
clear solution and only small amounts of decomposition
products of Fe2(CO)9. Successive filtration through a pad
of sand, Celite, and a micropore sized PTFE-filter (PTFE
) poly(tetrafluoroethylene)) yielded the crude complexes
14a ′/a ′′-14f′/f′′ and 15′/15′′ as bright yellow to orange
oils or solids in almost quantitative yield as mixtures
of diastereomers (for complexes 14a ′/a ′′-14f′/f′′: de )
15-70%; for complexes 15′/′′: de ) 12-16%). While
diastereomeric complexes 14a ,e-f (Table 1, entries 1,
5, and 6) were obtained in NMR spectroscopically pure
form, complexes 14b-d were subjected to chromato-
graphic purification on silica gel (collection of the yellow
bands) (Table 1, entries 2-4). This was accompanied
by partial decomposition of the products (Table 1,
entries 2-4) and a slight enrichment of the major
diastereomer (Table 1, entry 3). Conversion of alkene
(S)-8 to its diastereomeric mixture of complexes 15′ and
15′′ was incomplete in numerous cases. A range of 12-
23% of unreacted (S)-8 was always detected in the
isolated crude product (Table 1, entries 7 and 13).
The influence of polarity and coordination ability of
the solvent and the temperature on the diastereoselec-
tivity of the complexation of ligand (S)-6a to complexes
14a ′/a ′′ and (S)-8 to 15′/′′ was examined next (Table 1,
entries 8-13). Reaction in unpolar solvents such as
n-hexane or pentane proceeded slowly in favor of the
major diastereomer 14a ′ (quant. conversion, de ) 40-
70%). The diastereomeric excess of 14a ′ was signifi-
cantly improved by fractional crystallization from n-
hexane/diethyl ether mixtures at -22 °C (de ) ee >95
to >99%) (Table 1, entries 8 and 9). The conversion of
(S)-8 to complexes 15 could not be improved (Table 1,
entry 7 vs 13). More polar (CH2Cl2, THF) or aromatic
(toluene) solvents seemed to accelerate the reaction
(clear solution after ca. 3 h), but conversions of (S)-6a
to complexes 14a ′/a ′′ were incomplete (34-69% unre-
acted starting material), and only moderate diastereo-
meric excesses were obtained (de ) <3-39%) (Table 1,
a
Reagents and conditions: (a) 1.3 equiv of [Fe2(CO)9] (13),
solvent, room temp, 3 h to 3 days, CO atmosphere, exclusion
of light.
Syn t h esis of Tet r a ca r b on yl(η2-a lk en e)ir on (0)
Com p lexes 14 a n d 15. Anticipating that various
factors such as the nature of the leaving group moiety
(OPG ) leaving group) and the reaction conditions
strongly govern the diastereoselectivity of the complex-
ation reaction, we hoped to find a synthetically useful
set of reaction conditions to achieve highly diastereo-
selective complexation. Adapting a protocol developed
by Nicholas et al.,20r reaction of alkenes (S)-6a -f and
(S)-8 with a slight excess of nonacarbonyldiiron (13)
[Fe2(CO)9] in diethyl ether under an atmosphere of
carbon monoxide led to a gradual disappearance of the
insoluble Fe2(CO)9 (13) and yielded the corresponding
diastereomeric tetracarbonyl(η2-alkene)iron(0) com-
plexes 14a ′/a ′′-14f′/f′′ and 15′/15′′ (Scheme 3, Table 1,
entries 1-7).41,42 The reaction was stopped when the
(42) (a) Enders, D.; J andeleit, B. von Berg, S. Org. Synth. 2001, 78,
189. (b) Ref 21g.
(41) Braye, E. H.; Hu¨bel, W. Inorg. Synth. 1966, 8, 179.

4318 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
Ta ble 1. Com p lexa tion of th e Alk en es (S)-6a -f a n d (S)-8 to Th eir Cor r esp on d in g Dia ster eom er ic
(η2-Alk en e)tetr a ca r bon ylir on (0) Com p lexes 14a ′/a ′′-14f′/f′′ a n d 15′/′′
complexation of
entry
leaving group
ligands (S)-6/(S)-8
solvent
conditions
yield [%]
de [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
OBn
6a f 14a ′/a ′′
6b f 14b′/b′′
6c f 14c′/c′′
6d f 14d ′/d ′′
6e f 14e′/e′′
6f f 14f ′/f ′′
8 f 15′/15′′
6a f 14a ′/a ′′
6a f 14a ′/a ′′
6a f 14a ′/a ′′
6a f 14a ′/a ′′
6a f 14a ′/a ′′
8 f 15′/15′′
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
hexane
pentane
THF
CH2Cl2
toluene
hexane
Et2O
rt, 16 h
rt, 16 h
rt, 16 h
rt, 16 h
rt, 16 h
rt, 16 h
rt, 16 h
rt, 3 days
rt, 3 days
rt, 3 h
rt, 3 h
rt, 16 h
rt, 3 days
0 °C, 2 days
reflux, 3 h
reflux, 3 h
>90a (40-58)b
25-57c (>95)d
OBom
OTBDMS
OCH2C10H7
OH
OAc
OBn
OBn
OBn
OBn
OBn
(72)e
(18)f
(90)e
(15-16)f
(45)f
(48)e
quant.a
35c
93-98a (62)c
22-26c
12-16c
40-70c (>99)d
(>99)d
23c
77-88g
> 90a (40-64)b
(67),b (46)h
i,j
i,k
i,l
3
39
12
OBn
OBn
OBn
OBn
75m
n
6a f 14a ′/a ′′
6a f 14a ′/a ′′
6a f 14a ′/a ′′
Et2O
THF
i,o
i,o
OBn
a
Yield of the isolated crude, 1H NMR spectroscopically pure product. b In parentheses, yield after fractional crystallization from n-hexane/
Et2O mixtures. c Diasteroisomeric excess of the crude product determined by 1H NMR spectroscopy (300 MHz, C6D6). In parentheses,
d
diastereomeric excess determined after fractional crystallization from n-hexane/Et2O mixtures by 1H NMR spectroscopy (500 MHz, C6D6).
e In parentheses, yield after purification by column chromatography on silica gel determined by 1H NMR spectroscopy (300 MHz, C6D6).
f In parentheses, diastereomeric excess after purification by column chromatography on silica gel. g 12-23% of unconverted starting material
(S)-8 as determined by 1H NMR spectroscopy (300 MHz, C6D6). Isolated yield after second fractional crystallization. i Yield not determined.
h
34% of unconverted starting material (S)-6a as determined by 1H NMR spectroscopy (300 MHz, C6D6). 58-69% of unconverted starting
j
k
material (S)-6a as determined by 1H NMR spectroscopy (300 MHz, C6D6). 42% of unconverted starting material (S)-6a as determined by
l
1H NMR spectroscopy (300 MHz, C6D6). 25% of unconverted starting material (S)-8 as determined by H NMR spectroscopy (300 MHz,
m
1
C6D6). No reaction. o Decomposition of Fe2(CO)9.
n
entries 10-12). At 0 °C in diethyl ether, (S)-6a did not
react to give Fe2(CO)9 to give complexes 14a ′/a ′′ (Table
1, entry 14). At higher reaction temperatures, either in
refluxing diethyl ether or THF, the generation of side
products such as dodecacarbonyltriiron [Fe3(CO)12] was
generally observed, besides low diastereoselectivities (de
< 20%) (Table 1, entries 15 and 16). Hence, although
complexation of (S)-6a in n-hexane or pentane to give
complexes 14a ′ and 14a ′′ was subject to long reaction
times and some fluctuation with respect to diastereo-
meric excess of the crude materials (de ) 40-70%)
obtained, highly diastereo- and enantiomerically en-
riched material 14a ′ (de ) ee >95-99%) was obtained
routinely in 40-64% isolated yield after crystallization,
thus demonstrating this method to be synthetically
useful.
Deter m in a tion of Dia ster eom er ic Excesses a n d
Sp ectr oscop ic P r op er ties of Tetr a ca r bon yl(η2-a l-
k en e)ir on (0) Com p lexes 14a -f a n d 15. Complex-
ation of ligands (S)-6a -f and (S)-8 resulted in every case
in diastereomeric mixtures of tetracarbonyl(η2-alkene)-
iron(0) complexes 14a ′-f′ and 14a ′′-f′′ and 15′ and 15′′
(Table 1, Figures 3a-c). (Note: The descriptor ′ denotes
in all cases the major diastereomer, the descriptor ′′ the
minor diastereomer). Diastereomeric excesses were de-
termined by 1H and 13C NMR spectroscopy. Among
several other suitable proton NMR resonances, either
of the allylic scaffold or of the acceptor groups, the
doublet signal of the methyl group in complex mixtures
14a -f and 15 proved to be a particularly valuable “NMR
spectroscopical indicator”. All major diastereomers 14a′-
f′ exhibited a significantly downfield shifted doublet
resonance signal in comparison to the minor diastereo-
mers 14a ′′-f′′ (Figure 3a and Figure 3b). In contrast,
the major diastereomer 15′ showed an upfield shifted
methyl resonance (Figure 3c).
group unit, in n-hexane, pentane, or diethyl ether to give
complexes 14a ′/a ′′ (de ) 40-70% for repeated trials)
(Table 1, entries 1, 8, and 9). All other leaving group
combinations (OPG) for complexes 14b′/b′′-f′/f′′ were
inferior with respect to both control of diastereoselec-
tivity (de ) 15-45%) and practical ease (e.g., synthesis
of starting materials) (Table 1, entries 2-6, 10-12). The
modest diastereoselectivity and the complexation of
(S)-8 to complexes 15′/′′ could not be improved and
furnished mixtures of diastereomeric complexes 15′ and
15′′ in every case (average de ∼12%, conversion of (S)-8
ca. 77-88%) (Table 1, entries 7 and 13).
IR spectroscopic analysis of complexes 14a -f and 15
displayed up to four Fe-CO valence vibrations in the
range of ν ) 1990-2100 cm-1 with the most energetic
absorption at ν ) ca. 2100 cm-1, which can be assigned
to an axially bound CO group. These results indicate
clearly that compounds 14a -f and 15 are monomeric
and, generally, the Fe(CO)4L fragments of 14a -f and
15 have a trigonal bipyramidal structure where the
olefinic ligands lie in an equatorial position. Mass
spectroscopic analysis of complexes 14a -f and 15
displayed a distinct fragmentation pattern due to suc-
cessive loss of CO ligands [M•+ - (CO)n (n ) 1-4)] with
a high relative intensity for the fragment M•+ - (CO)4,
which degenerates further either by loss of the protect-
ing group unit (PG) or by â-elimination of a HOPG
moiety.
NMR spectroscopic studies (1H-13C HETCOR) of
complexes 14a -f and 15 revealed the expected high-
field shift of the “olefinic” hydrogen and carbon atoms
upon complexation. This reflects a partial change in the
hybridization state of the “olefinic” carbon atoms (sp2
f sp3) causing an elongation of the CdC bond distance
and a change from double bond to single bond character.
3
The J trans coupling constants for the AB system (HR)-
Best diastereomeric excesses were obtained for com-
plexation of ligand (S)-6a , bearing the OBn leaving
(Hâ) of the complexed olefinic bond are decreased from
ca. 15 Hz in alkenes (S)-6a -f and (S)-8 to 10-11 Hz in

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4319
1
F igu r e 3. (a) H NMR doublet signals of the CH3 group connected to the carbon C(3) of a mixture of diastereomeric
1
complexes 14a ′ and 14a ′′ (300 MHz, C6D6, de ) 74%). (b) H NMR doublet signal of the CH3 group of a diastereo- and
enantiopure sample of complex 14a ′ (500 MHz, C6D6, de ) ee > 99%). (c) 1H NMR doublet signals of the CH3 group connected
to the C(3) carbon of a mixture of starting material (S)-8 and diastereomeric complexes 15′ and 15′′ (300 MHz, C6D6, de
) 16%). (Note: The descriptor ′ denotes the major diastereomer, and the descriptor ′′ the minor diastereomer.)
Ta ble 2. NMR Sp ectr oscop ic Deta ils of Un com p lexed Liga n d s (S)-6a /(S)-8 a n d Th eir Cor r esp on d in g
(η2-Alk en e)tetr a ca r bon ylir on (0) Com p lexes 14a ′/14a ′′ a n d 15′/15′′
entry
compound
δ(HR) [ppm]
δ(Hâ) [ppm]
3J trans [Hz]
δ(CR) [ppm]
δ(Câ) [ppm]
1
2
3
4
5
6
(S)-6a a
14a ′b
14a ′′b
(S)-8c
15′a
6.52
3.86
3.76
6.03
4.20
4.12
6.94
3.29
3.30
6.89
3.85
3.80
14.8
10.3
10.4
15.8
11.0
10.9
131.21
66.71
65.52
120.85
66.29
63.92
147.09
57.96
59.23
149.51
42.95
44.78
15′′a
a
b
1H NMR spectra recorded in C6D6 at 300 MHz; 13C NMR spectra recorded in C6D6 at 75 MHz. 1H NMR spectra recorded in C6D6
at 500 MHz; 13C NMR spectra recorded in C6D6 at 125 MHz. c1H NMR spectra recorded in CDCl3 at 500 MHz; 13C NMR spectra recorded
in CDCl3 at 125 MHz.
complexes 14a -f and 15. A particularly characteristic
feature is the upfield shift of the signals of the atoms
at the â-position [tC(2)] of the alkenyl systems relative
to those at the R-position [tC(1)] with respect to the
acceptor group (SO2Ph or CO2Me) in comparison to the
corresponding free alkenes (S)-6a -f and (S)-8 (Table 2).
For comparable cyclic tetracarbonyl(η2-alkene)iron(0)
complexes possessing naturally a (Z)-configured double
bond this change is not observable.23,43 The proton NMR
spectroscopic observations are all in accordance with a
partial “ferracyclopropane” substructure of the (η2-
alkene)Fe(CO)4 unit, allowing assignment of absolute
configurations of the stereogenic centers at the com-
plexed “olefinic” carbon atoms according to the Cahn-
Ingold-Prelog notation (vide supra).44
The CO ligands gave a single broad 13C NMR reso-
nance signal at δ ca. 207 ppm indicative of their rapid
exchange by Berry pseudorotation. All NMR experi-
ments established that the complexes show no tendency
to epimerize in solution at room temperature. In con-
trast, we and Speckamp et al. described a slow isomer-
ization of cyclic tetracarbonyl(η2-alkene)iron(0) com-
plexes in dichloromethane.23,43
Deter m in a tion of th e Molecu la r Str u ctu r e of
Com p lexes 14a ′ a n d 14a ′′ a n d Assign m en t of th e
Absolu te Con figu r a tion s of Com p lexes 14a -f a n d
15. Only few sulfonyl-substituted tetracarbonyl(η2-al-
kene)iron(0) complexes have been described in the
literature so far.45 Complex 14a ′ was obtained by
fractional crystallization from partly concentrated solu-
tions (n-hexane/diethyl ether) at -22 °C in virtually
diastereo- and enantiomerically pure form (de ) ee >
99%) as pale yellow needles or plates (vide infra).21g,42
The minor diastereomer 14a ′′ was obtained as well by
repeated crystallization from concentrated mother li-
quors (light petroleum/diethyl ether) in virtually di-
astereo- and enantiomerically pure form (de > 99% by
NMR) as pale yellow needles. The molecular structures
of both complexes, 14a ′ (major diastereomer) (Figure 4),
and 14a ′′ (minor diastereomer) (Figure 5), were deter-
mined by X-ray crystallography.21g,46 The molecular
(45) (a) Guilard, R.; Dusalisoy, Y. J . Organomet. Chem. 1979, 77,
393. (b) McCaskie, J . E.; Chang, P. L.; Nelson, T. R.; Dittmer, D. C. J .
Org. Chem. 1973, 38, 3963. (c) Nesmeyanov, A. N.; Rybin, L. V.;
Rybinskaya, M. I.; Gubenko, N. T.; Leshcheva, I. F.; Ustynyuk, Y. A.
J . Gen. Chem. USSR (Engl. Transl.) 1968, 38, 1428. (d) Ibbotson, A.;
Reduto dos Reis, A. C.; Saberi, S. P.; Slawin, A. M. Z.; Thomas, S. E.;
Tustin, G. J .; Williams, D. J . J . Chem. Soc., Perkin Trans. 1 1992,
1251.
(46) Suitable crystals for the X-ray structure determination were
obtained from diethyl ether/petroleum ether at 4 °C. C21H18O7SFe,
crystal dimensions ca. 0.4 × 0.4 × 0.2 mm, monoclinic, space group
P21(4), a ) 6.503(2) Å, b ) 7.209(3) Å, c ) 23.091(6) Å, â ) 93.40(1)°,
V ) 1080.6 Å3, Z ) 2, Mcalcd ) 470.28, Fcalcd ) 1.445 g cm-3. Total
(43) Enders, D.; Schmitz, T.; Raabe, G.; Kru¨ger, C. Acta Crystallogr.
1991, C47, 37.
(44) Helmchen, G. In Methods of Organic Chemistry; Houben-Weyl,
1995; Vol. E, p 21a. (b) Prelog, V.; Helmchen, G. Angew. Chem. 1982,
94, 614; Angew. Chem., Int. Ed. Engl. 1982, 21, 567. (c) Cahn, R. S.;
Ingold, C.; Prelog, V. Angew. Chem. 1966, 78, 413.

4320 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
the terminal methyl group is slightly inclined toward
the Fe atom (C(1)-C(2)-C(3)-C(4) -151(1)°) (Figure
4). The complexed ligand adopts a “W”-shaped geometry,
counting from the terminal methyl group to the sulfur
atom (Figure 2, structure D and Figure 4), demonstrat-
ing conservation of (E)-double bond geometry of the
complexed ligand (S)-6a . As a result of the absolute
configuration at the 3-position, the side of the double
bond unit is selectively blocked by the Fe(CO)4 moiety,
which lies trans or anti with respect to the OBn leaving
group.
Many attempts to isolate crystals of sufficient quality
for a clean refinement of the structure of complex 14a ′′
met with failure. Only poorly diffracting samples could
be obtained in this case, and consequently, the number
of observed reflections was too low to allow anisotropic
refinement of the solved structure. Although no detailed
discussion of structural parameters is possible under
these conditions, the isotropically refined structure not
only proves the molecule’s constitution but also gives a
good impression of its absolute configuration (Figure 5).
F igu r e 4. Molecular structure of the major diastereomer
14a ′ (SCHAKAL representation).48
The benzyloxy group, the phenylsulfonyl group, and
the bulky tetracarbonyliron moiety are the most steri-
cally demanding groups. Hence, these groups are ar-
ranged in a particular fashion whereby they are as far
apart as possible from each other. In the minor diaste-
reomer 14a ′′ the phenylsulfonyl unit and the terminal
methyl group are twisted away from the Fe(CO)4 moiety,
resulting in an “S”-shaped geometry (S t sickle) of the
(carbon) skeleton (Figure 2, structure C and Figure 5).
Here, the leaving group unit is now positioned in the
plane defined by C(2)-C(3)-C(4). In general, all topo-
logical features and structural parameters correlate
with experimental and analytical data found for related
acceptor-substituted tetracarbonyl(η2-alkene)iron com-
plexes including a distorted trigonal bipyramidal ge-
ometry, an unsymmetrically coordinated double bond,
and a perpendicular relation of the planes through C(3),
C(4), Fe, C(20), and C(21) and the plane defined by
atoms C(18), Fe, and C(19) (Figures 4 and 5).21g,23,43,45,49
F igu r e 5. Molecular structure of the minor diastereomer
14a ′′ (SCHAKAL representation).48
structure of complex 14a ′ was solved according to the
Patterson method (SHELXS-86) and employing the
Xtal3.2 program package for additional crystallographic
calculations.47 Some structural aspects concerning the
stereochemistry of the ligands complexed in 14a ′ and
14a ′′ and the conformation of their (carbon) backbones
merit closer inspection (Figures 4 and 5).
(Note: The atomic numbering scheme of Figure 4 and
Figure 5 is different from the numbering scheme in
Figure 2 (structures F and G). Carbon atom C(4) in
Figure 4 or 5 corresponds to carbon atom C(1) in Figure
2, C(3) in Figure 4 or 5 corresponds to carbon atom C(2)
in Figure 2, and C(2) in Figure 4 or 5 corresponds C(3)
in Figure 2).
The most significant differences between the diaster-
eomers 14a ′ and 14a ′′ are the different diastereotopici-
ties of the double bond complexed and, therefore, the
adoption of different conformations around the single
bond between the double bond and the carbinol atom
bearing the leaving group unit (OPG) (Figures 2, 4, and
5). In related cyclic systems the complexation seems
kinetically to favor the sterically more hindered cis
products (Ψ-endo, Figure 2).23,43 Apparently, the ob-
served trans selectivity (Ψ-exo, Figure 2) in the ex-
amples examined might be the result of thermodynamic
equilibration.
The SO2Ph unit of complex 14a ′ is twisted away from
the Fe(CO)4 moiety (C(2)-C(3)-C(4)-S -137(1)°), and
(Note: For the assignment of the absolute configura-
tion of the coordinated carbon atoms of the complexes
14a ′ and 14′′ the atomic numbering scheme of Figure 2
is used).
number of electrons per unit cell F(000) ) 484, Mo KR radiation (λ )
0.71073 Å, graphite monochromator), µ ) 8.26 cm-1, no absorption
correction, Enraf-Nonius four-circle diffractometer, Ω/2θ scans, 20 °C;
2670 independent reflections (( h + k + l), of which 1279 observed (I
> 2σ(I)), Rav ) 0.07, sin θ/λmax ) 0.649. Structure solution according
to Patterson methods (SHELXS-86), all other crystallographic calcula-
tions were carried out with the Xtal3.2 program package.49 Positions
of hydrogen atoms calculated; 270 refined parameters, R ) 0.068, (Rw
) 0.073), residual electron density -1.3/ +1.3 e Å-3. Further details
of the crystal structure investigation may be obtained from the
Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopold-
shafen (FRG), on quoting the depository number CSD-58339.
(47) (a) Sheldrick, G. M. SHELXS-86; University of Go¨ttingen, 1986.
(b) Hall, S. R.; Flack, H. D.; Stewart, J . M. Xtal3.2 Reference Manual;
Universities of Western Australia (Perth), Geneva, Maryland; Lamb:
Perth, 1992.
The crystallographic structure determination of com-
plexes 14a ′ and 14a ′′ and the NMR spectroscopic results
clearly indicate the relative arrangement of the leaving
group unit (OPG) bond on the carbinol atom C(3) and
the Fe(CO)4 moiety in complexes 14a -f and 15. This
information allows as well for the designation of the
absolute configuration of the newly generated stereo-
genic centers of the coordinated double bond of com-

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4321
Sch em e 4. Syn th esis of Dia ster eom er ic Syn - a n d
An ti-Con figu r ed (η3-Allyl)tetr a ca r bon ylir on (1+)
Com p lexes 17 fr om Ra cem ic Secon d a r y Allylic
(Figure 6). Cleavage of the C-O bond of the OPG
leaving group of structures A and C supposedly proceeds
with formation of a new C-Fe bond and inversion of
the absolute stereochemistry at C(3). Cleavage of the
OPG group of the “W”-shaped complex A should result
in the stereospecific generation of the syn-Me,syn-Acc-
configured cationic complex B. Analogous treatment of
complex C should yield a (η3-allyl)tetracarbonyl species
D with a syn-configured acceptor group and an anti-
configured methyl group (anti-Me,syn-Acc). Therefore,
diastereomeric structures B and D both possess the
identical absolute configuration at carbon atom C(3).
Syn-configured allyl complexes are thermodynamically
more stable than the corresponding anti-configured
complexes, and numerous (π-allyl)metal complexes es-
pecially those derived from palladium undergo rapid
anti f syn isomerization processes prior to the nucleo-
philic attack.50 Isomerization of the anti-Me-configured
structure D to the syn-Me-configured complex may
proceed via a π-σ-π mechanism and would lead to
structure B with conservation of the absolute configu-
ration at C(3) (double inversion) possibly involving an
intermediate enyl structure E, where the Fe(CO)4
moiety is both σ- and π-bound to the organic ligand.51
On the other hand, an anti-Me f syn-Me isomerization
mechanism without migration of the Fe(CO)4 moiety to
the other enantiotopic face of the double bond would
lead to structure ent-B with inverted absolute configu-
ration at C(3) (epimerization process).
Syn th esis of (η3-Allyl)tetr acar bon ylir on (1+) Com -
p lexes 18 a n d 19. Ether solutions of diastereomerically
enriched or pure (η2-alkene)tetracarbonyliron(0) com-
plexes, 14a ′/a ′′, 14f′/f′′, and 15′/′′ were treated with a
slight excess of a solution of anhydrous tetrafluoroboric
acid in diethyl ether to cleave the OPG leaving group
unit (Scheme 5, Table 3).20r,21g,42 The corresponding (η3-
allyl)tetracarbonyliron(1+) complexes 18′/′′ and 19′/′′
immediately precipitated as yellow-white solids and
were obtained as mixtures of diastereomers in NMR
spectroscopically pure form. Further purification pro-
cedures such as precipitation from nitromethane solu-
tion with cold diethyl ether resulted in substantial loss
of material and led to selective enrichment of syn-Me-
configured isomers.
a
Alcoh ols 1620r
a
Reagents and conditions: (a) 1.0 equiv of [Fe2(CO)9] (13),
Et2O, room temp, 10 h, CO atmosphere. bHBF4 in HOAc/Ac2O,
room temp, 15 min.
plexes 14a -f and 15 [at C(4) and C(3) in Figure 4 or
Figure 5; C(1) and C(2) according to structures F and
G in Figure 2]. In the major diastereomer 14a ′ the
absolute configuration of carbon atom C(1) can be
assigned to be (R) according to the Cahn-Ingold-Prelog
notation.44 Since carbon atom C(2) is not independent
from C(1) [(R)], its configuration must be consequently
assigned to be (S). It is sufficient to assign only one
stereochemical descriptor for the complexed double
bond, e.g., 14a ′ t (1R,2S,3S)-14a t (1R,3S)-14a . For
the minor diastereomer, similar conclusions lead to the
assignment (1S,2R,3S) [14a ′′ t (1S,2R,3S)-14a
t
(1S,3S)-14a ]. In analogy with these results, all major
diastereomers 14a ′-f′ possess the absolute configura-
tion (1R,2S,3S), and consequently, all minor diastere-
omers 14a ′′-f′′ possess the absolute configuration
(1S,2R,3S). As a consequence of a lower ranking Cahn-
Ingold-Prelog priority of the methoxycarbonyl func-
tionality in complexes 15, the major diastereomer 15′
possesses the absolute configuration (1R,2S,3S), show-
ing that in this case the structure with the “S”-shaped
backbone is slightly favored. The minor diastereomer
15′′ possesses consequently the (1S,2R,3S)-configura-
tion. According to Figure 2, complexes (1R,2S,3S)-14a -f
(14a ′-f′) and (1S,2R,3S)-15 (15′′) should conform with
The diastereomerically pure complex 14a ′ (de, ee >
99%) gave the tetracarbonyl iron complex 18′ in virtu-
a
Ψ-exo-14a -f, 15 assignment, while complexes
(1S,2R,3S)-14a -f (14a ′′-f′′) and (1R,2S,3S)-15 (15′)
should conform with an Ψ-endo-14a -f, 15 assignment.
Tetr acar bon yl(η3-allyl)ir on (1+) Com plexes: Ster -
eoch em ica l Con sid er a tion s. It has been demon-
strated that conversion of secondary allylic alcohols of
type rac-16 into their corresponding methyl- or phenyl-
substituted tetracarbonyl(π-allyl)iron(1+) complexes 17
gave rise to diastereomeric mixtures of syn-R and anti-R
isomers (Scheme 4).20r (E)-Configured alkenes gave
stereospecifically syn-configured and (Z)-configured al-
kenes gave stereospecifically anti-configured (π-allyl)-
tetracarbonyliron cation complexes. The formation of the
intermediate tetracarbonyl(η2-alkene)iron(0) complexes
supposedly followed stereochemical pathways similar to
those described in the previous sections.
(48) Keller, E. SCHAKAL 86; University of Freiburg, 1986.
(49) (a) Cano, A. C.; Zu´n˜iga-Villarreal, N.; Alvarez, C.; Toscano, T.
R. A.; Cervantes, M.; Diaz, A.; Rudler, H. J . Organomet. Chem. 1994,
464, C23. (b) Chow, T. J .; Hwang, J .-J .; Wen, Y.-S.; Lin, S.-C. J . Chem.
Soc., Dalton Trans. 1994, 937. (c) Rybin, L. V.; Rybinskaya, M. I. Russ.
Chem. Rev. 1993, 62, 637. (d) Liu, L.-K.; Sun, C.-H.; Yang, C.-Z.; Wen,
Y.-S.; Wu, C.-F.; Shih, S.-Y.; Lin, K.-S. Organometallics 1992, 11, 972.
(e) Hsiou, Y.; Wang, Y.; Liu, L.-K. Acta Crystallogr. 1989, 45, 721. (f)
Lei, P.-S.; Vogel, P. Acta Crystallogr. 1986, 5, 2500. (f) Whitesides, T.
H.; Slawen, R. W.; Calabrese, J . C. Inorg. Chem. 1974, 13, 1895. (g)
Luxmoore, A. R.;. Truter, M. R. Acta Crystallogr. 1962, 15, 1117.
(50) For an example see: Lin, S.-H.; Chen, C.-C.; Vong, W.-J .; Liu,
R.-S. Organometallics 1995, 14, 1619. For
a thermodynamically
preferred anti-configurated (η3-allyl)dicarbonyl[hydrotris(1-pyrazolyl)-
borato]molybdenum complex see: Ward, Y. D.; Villanueva, L. A.;
Allred, G. D.; Payne, S. C.; Semones, M. A.; Liebeskind, L. S.
Organometallics 1995, 14, 4132.
(51) Enyl complexes are by definition those that contain discrete σ-
and π-metal carbon interactions within a single ligand. Sharp, P. R.
In Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995;
Chapter 2, p 272. Enyl complexes are discussed as intermediates for
example in Rh-, Ir-, and Fe-catalyzed allylic substitutions with chirality
transfer. See refs 7, 8, 14.
We proposed an overall stereochemical scheme for the
transformation of (η2-alkene)tetracarbonyliron(0) com-
plexes of type 14a -f and 15 to their corresponding
cationic (η3-allyl)tetracarbonyliron(1+) complexes

4322 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
F igu r e 6. Working hypothesis: Acidic cleavage of the OPG leaving group unit from either structure A (“W”-shaped) or
B (“S”-shaped) supposedly yields stereospecifically structures C and D and proceeds with formal formation of a C-Fe
bond and inversion of the absolute stereochemistry at carbon atom C(3). Structure D may isomerize to the thermodynami-
cally favored structure B or ent-B with the syn-configured methyl group. A π-σ-π mechanism, involving possibly an
enyl-structure E, would proceed with an overall retention (double inversion) of stereochemistry at carbon atom C(3). Anti-
Me to syn-Me isomerization of structure D with an inversion of absolute stereochemistry only at carbon atom C(3) should
result in the formation of structure ent-B (epimerization). Cahn-Ingold-Prelog (CIP) priority: C(1) > C(2). Abbrevia-
tions: HY: strong acid with noncoordinating anion. σ: mirror plane.
Sch em e 5. Syn th esis of Dia ster eom er ic (η3-Allyl)tetr a ca r bon ylir on (1+) Com p lexes 18′/′′ a n d 19′/′′a
a
Reagents and conditions: (a) 1.0 equiv of of complex 14a ′/a ′′, 14f′/f′′ or 15′/′′, 1.3 equiv of 54% HBF4 in Et2O, 30 °C, 1 h.
Abbreviations: ent: enantiomeric form.
ally quantitative yield (>95%) as a single syn-Me,syn-
SO2Ph-substituted diastereomer (syn-Me/anti-Me > 99:
1, de > 99%) according to 1H NMR spectroscopic
analysis (Table 3, entry 1). The transformation of
(1R,2S,3S)-14a (14a ′) to 18′ proceeded with conservation
of the (E)-double bond geometry, leading to a syn-
configured SO2Ph group and retaining the overall “W”-
shaped appearance of the allylic ligand (syn-Me) (Figure
6). Transformation of mixtures of complexes 14a ′/a ′′
with various diastereomeric excesses (de ) 42 or 30%)
in favor of the diastereomer 14a ′ yielded diastereomeric
mixtures of the cationic complexes 18′ and 18′′, albeit
in lower isolated yield of 74 and 68% (Table 3, entries 2
and 3). 1H NMR spectroscopic analysis of these samples
showed that each material was obtained as a pure syn-
Me,syn-SO2Ph-configured allyl complex 18′ containing
basically no traces of the corresponding anti-Me,syn-
SO2Ph diastereomers 18′′. Complete mass transfer and
the absence of isomerization processes for these trans-
formations suggest theoretically a syn-Me/anti-Me ratio

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4323
Ta ble 3. Con ver sion of Dia ster eom er ic Mixtu r es of (η2-Alk en e)tetr a ca r bon ylir on (0) Com p lexes 14a ′/a ′′,
14f′/f′′, a n d 15′/′′ to th e Cor r esp on d in g Mixtu r es of Dia ster eom er ic (η3-Allyl)tetr a ca r bon ylir on (1+)
Com p lexes 18′/′′ a n d 19′/′′
conversion
dec
14, 15 [%]
yieldd
18, 19 [%]
syn-Me/
def
18, 19 [%]
syn-Me/anti-Meg
entry
OPGa
14, 15 f 18, 19b
anti-Mee
de [%]g
1
2
3
4
5
6
7
OBn
OBn
OBn
OBn
OAc
OAc
OBn
14a ′/a ′′ f 18′/′′, ent-18′
14a ′/a ′′ f 18′/′′, ent-18′
14a ′/a ′′ f 18′/′′, ent-18′
14a ′/a ′′ f 18′/′′, ent-18′
14f′/f′′ f 18′/′′, ent-18′
[rac-6f f] 14f′/f′′k f rac-18′/′′
15′/15′′ f 19′/′′
>99h
42h
>95
74
68
58
64
>99:1i
99i
99i
99i
15
51
49
99:1 (99)
2.45:1 (42)
1.86:1 (30)
1:7.0 (75)
1.63:1 (24-26)
l
ca. 1:1.3
(ca. 13)
l
>99:1i
30h
>99:1i
1:1.36
3.11:1
2.94:1
75j
24-26h
l
80-94m
95n
12-16
1:1.27-1:1:38
12-16
8
OBn
[(S)-8 f] 15′/′′o f19′/′′
10h
87
1:1.19
9
a
b
PG: protecting group. Reagents and conditions: 1.0 equiv of complex 14a ′/a ′′, 14f′/f′′, or 15′/′′, 1.3 equiv of 54% HBF4 in Et2O, 30
°C, 1 h. c Diastereomeric ratios of complexes 14 and 15 determined by 1H NMR spectroscopy (300 MHz, C6D6). See Table 1 for details.
d
Yield of isolated material in 1H NMR spectroscopically pure form. e Unless otherwise stated, syn-Me/anti-Me ratios of complexes 18′/′′
and 19′/′′ determined by 1H NMR spectroscopy (300 MHz, d3-nitromethane). f Unless otherwise stated, diastereomeric excesses of complexes
18′/′′ and 19′/′′ determined by 1H NMR spectroscopy (300 MHz, d3-nitromethane). Theoretically expected syn-Me/anti-Me ratio or, in
g
h
i
parentheses, diastereomeric excesses. Diastereomeric excesses of complexes 14a ′/f′ over complexes 14a ′′/f′′. No traces of the minor
diastereomer detectable by high-resolution 1H NMR spectroscopy (500 MHz, d3-nitromethane). Diastereomeric excess of complex 14a ′′.
j
k
l
m
Obtained from rac-6f and used as a crude complex mixture 14f′/f′′ as starting material. Not determined. Averaged yields over 2
steps starting from rac-6f. Averaged yield of isolated material from several trials. o Obtained from (S)-8 and used as a crude complex
n
mixture 15′/′′ as starting material.
of 2.45:1 or 1.86:1 (Table 3, entries 2 and 3). A sample
of complex 14a with a diastereomeric excess of 75%
favoring the diastereomer (1S,2R,3S)-14a (14a ′′) gave
allyl complex 18 in only 58% yield as a mixture of syn-
Me/anti-Me-configured diastereomers in a ratio of 1:1.36
(theoretically expected value 1:7.0) (Table 3, entry 4).
A sample of a diastereomeric mixture of the acetoxy-
substituted (η2-alkene)tetracarbonyliron complex 14f′/
f′′ (de ca. 25%) was converted in 64% yield to a
diastereomeric mixture of complexes 18′/′′ (Table 3,
1
entry 5). H NMR experiments showed a syn-Me/anti-
Me ratio of 3.11:1 (de ) 51%), which differs significantly
from the theoretically calculated values of a syn-Me/
anti-Me ratio of 1.63:1 (de ) 24-26%). The result was
confirmed by reacting a racemic sample of alkene 6f
F igu r e 7. Details of the 1H-1H proton NMR coupling
(rac-6f) in 80% overall yield via a diastereomeric
pattern of diastereomeric (η3-allyl)Fe(CO)4(1+) complexes
mixture of complexes rac-14f′/f′′directly to a diastere-
18′/′′ and 19′/′′ (300 MHz, d3-nitromethane).
omeric mixture of complexes rac-18′/′′ [syn-Me/anti-Me
2.94:1 (de ) 49%)] (Table 3, entry 6).52
complexes 15′/′′ proceeded stereospecifically and without
Several purified samples of the methoxycarbonyl-
suffering any significant anti-Me f syn-Me isomeriza-
substituted (η2-alkene) complexes 15′/′′ (de ) 12-16%)
tion. 1H NMR experiments showed that the syn-Me/anti-
gave quantitatively mixtures of allyl complexes 19′/′′ [19′
Me ratio of mixtures of complexes 18′/′′ changed slowly
t anti-Me,syn-CO2Me-19, 19′′ t syn-Me,syn-CO2Me-19]
to favor the syn-Me-substituted complex 18′ at 4 °C, but
in ratios of ca. 1:1.3 (de ) 12-16%) but in favor of the
partial decomposition prevented a detailed kinetic
anti-Me,syn-CO2Me isomer 19′ (Table 3, entry 7). Pro-
investigation.
tonation of a diastereomeric mixture of complexes 15′/′′
NMR Sp ectr oscop ic P r op er ties a n d Assign m en t
(de ) 10%), which was obtained directly from (S)-8 and
of th e Rela tive a n d Absolu te Con figu r a tion of th e
used without prior purification, yielded a mixture of the
(η3-Allyl)F e(CO)4(1+) Com p lexes 18′/′′ a n d 19′/′′. The
syn-Me,syn-CO2Me- and the anti-Me,syn-CO2Me-con-
syn-Me,syn-SO2Ph- or syn-Me,syn-CO2Me-configured
figured allyl complexes 19′/′′ in a ratio of 1:1.19 (de )
complexes (18′, ent-18′, and 19′′) and the anti-Me,syn-
9%), again in favor of the anti-Me,syn-CO2Me isomer
SO2Ph- or anti-Me,syn-CO2Me-configured complexes
19′ (Table 3, entry 8). For entries 7 and 8 (Table 3), the
1
(18′′ and 19′) show clearly distinguishable H and 13C
diastereomeric excesses or (syn-Me/anti-Me ratios) of the
NMR resonances. In anionic, neutral, or cationic(η3-
complex mixtures 19′/′′ (de ) 12-16%, de ) 9%) coincide
allyl)MLn complexes anti-configured methyl groups ap-
with sufficient accuracy with the diastereomeric ex-
pear invariably shifted upfield with respect to syn-
cesses of the starting materials 15′/′′ (de ) 12-16%,
configured methyl groups.10b,20h,21,51,53 All 3J 1H-1H
de ) 10%). It was therefore concluded that in contrast
coupling constants for the [C(1)-HR]-[C(2)-Hâ], [C(2)-
to the conversion of complexes 14a ′/a ′′ or 14f′/f′′ to allyl
Hâ]-[C(3)-Hγ], and [C(3)-Hγ]-Me couplings are char-
complexes 18′/′′, formation of complexes 19′/′′ from
acteristic for the diastereomeric syn-Me- and anti-Me-
configured complexes 18 and 19 and allow unam-
(52) Alkene rac-6f was synthesized according to refs 34, 35 and
obtained in 83% isolated yield from racemic 2-acetoxypropanal (gift
biguously to distinguish between them (Figure 7).20,21
from BASF AG) and the phenylsulfonyl-substituted phosphonate 5.
NOE (nuclear Overhauser enhancement) NMR analysis

4324 Organometallics, Vol. 20, No. 21, 2001
Ta ble 4. Deta ils of th e 1H a n d 13C NMR Sp ectr a of Com p lexes 18′/′′ a n d 19′/′′
Enders et al.
δ[C(1)-HR]
δ[C(2)-Hâ]
δ[C(3)-Hγ]
δ[C(1)]
[ppm]
δ[C(2)]
[ppm]
δ[C(3)]
[ppm]
entry
complexa
[ppm]
[ppm]
[ppm]
1
2
3
4
18′
18′′
19′
19′′
4.64
5.30
4.27
3.64
6.23
6.12
6.24
6.35
4.93
5.85
5.88
4.97
73.73
77.73
57.85
53.38
97.65
94.46
97.53
90.58
92.56
90.60
89.26
100.83
a
HETCOR NMR spectroscopic measurements performed on mixtures of complexes 18′/′′ and 19′/′′; 1H NMR (500 MHz), 13C NMR (125
MHz) (d3-nitromethane).
of complex 18′ confirmed the close proximity of the
[C(2)-Hâ] atom and the syn-configured methyl group.
Due to the electron-withdrawing character of the Fe-
(CO)4 moiety and the overall positive charge, the cat-
ionic complexes 18 and 19 display a remarkable down-
field shift for the allylic protons (Table 4).
and 18′′ t anti-Me,syn-SO2Ph-18 t (1S,2R,3R)-18 t
(1S,3R)-18. The species ent-18′ represents ent-(syn-
Me,syn-SO2Ph)-18, therefore possessing the absolute
configuration (1S,2R,3S)-18 t (1S,3S)-18 (Scheme 5,
Figure 6). As a consequence of a minor Cahn-Ingold-
Prelog priority of the methoxycarbonyl functionality in
complexes 19′/′′, the major diastereomer 19′ t anti-
Me,syn-CO2Me-19 possesses the absolute configuration
(1R,2S,3R), which is derived from the neutral (η2-
alkene)tetracarbonyliron complex 15′ with the “S”-
shaped backbone. The minor diastereomer 19′′ t syn-
Me,syn-CO2Me-19 possesses consequently the (1S,2R,3R)
absolute configuration (Scheme 5, Figure 6). Each allyl
complex (1R,2S,3R)-18 and (1S,2R,3R)-18, or (1R,2S,3R)-
19 and (1S,2R,3R)-19 possesses an absolute (R) config-
uration at C(3), which means that they possess identical
stereochemistry at C(3). The exception is the optical
antipode of complex 18′, epimerization product ent-18′,
which has an inverted absolute configuration (1S,2R,3S).
In most of the (η3-allyl)MLn complexes described in
the literature, the 13C resonance of the central C(2) atom
exhibits a significant downfield shift.6,10b,21,51,54 1H-13C
correlation NMR spectroscopy (HETCOR) on complexes
18′ and 18′′ showed that the C(2) atom is indeed the
most downfield shifted. This trend was observed for both
diastereomers (Table 4). The closely related substitution
pattern of complexes 19′ and 19′′ allowed for a similar
chemical shift assignment.
The 13C NMR spectroscopic chemical shift of the
methyl-substituted allylic termini [C(3)] found at 89-
92 ppm (Table 4) can be explained by a deshielding
R-effect of the methyl substituent (R-effect +20-30
ppm). Four distinguishable 13C NMR resonance signals
in the range from 195 to 199 ppm were observed,
indicating both the monomeric character and the high
rotational energy barrier at ambient temperature of 18
and 19.
Nu cleop h ilic Ad d it ion R ea ct ion s of Silyl E n ol
Eth er 20 a n d Silyl Keten e Aceta l 21 to Tetr a ca r -
bon yl(π-a llyl)ir on Com p lexes 18 a n d 19. The enan-
tiomeric excesses of the cationic iron complexes 18 and
19 could not be determined directly by use of, for
example, chiral NMR shift reagents. It was hoped to
draw a conclusive correlation between enantiomeric
purity and absolute stereochemistry of complexes 18′/′′
and 19′/′′ on one hand and products obtained after
addition of test nucleophiles to them on the other.
Among the multitude of nucleophiles known to add to
cationic allyl iron complexes of type 18 and 19,20-24 soft
carbon nucleophiles such as silyl enol ethers or silyl
ketene acetals react in a particularly clean manner.
Mixtures of (η3-allyl)tetracarbonyliron(1+) complexes
18′/′′ and 19′/′′ of different diastereomeric purity were
chosen to react with an excess of two different test
nucleophiles 20 and 21 (Scheme 6, Table 5).43,55 The
suspended cationic complexes gradually dissolve upon
addition of the carbon nucleophiles to furnish initially
the soluble intermediate neutral substituted (η2-alkene)-
tetracarbonyliron(0) complexes. Oxidative removal of
the tetracarbonyliron moiety with ceric ammonium
nitrate (CAN) (22) yielded the known 3-substituted
alkenyl sulfone (R)-23 and 3-substituted ester (S)-24,
which were isolated after workup and chromatographic
purification in excellent to good yield (Table 5).21b,f
The transformation of ligands (S)-6 and (S)-8 via the
neutral diastereomeric (η2-alkene)tetracarbonyliron com-
plexes 14 and 15 to the corresponding cationic (η3-
alkene)tetracarbonyliron complexes 18 and 19 pro-
ceeded with retention of the double bond geometry,
positioning the acceptor group in a syn-configura-
tion.20,21 Therefore, only the two diastereomers with a
syn-Me,syn-Acc or anti-Me,syn-Acc substitution pattern
become plausible (Figure 6). Each diastereomer obtained
should be for itself enantiomerically pure. Stereo-
chemical descriptors are necessary to assign their
absolute and relative stereochemistry correctly.
According to the Cahn-Ingold-Prelog notation and
assuming conservation of topicity of the Fe(CO)4 moiety
during the transformation (1R,2S,3S)-14a (14a ′) f 18′,
the absolute configuration of carbon atom C(1) of the
major diastereomer complex 18′ was assigned to be (R)
and carbon atom C(2) to be (S) (Figure 4). Cleavage of
the OPG leaving group (OBn) unit at carbon atom C-3
in the transformation 14a ′ f 18′ supposedly proceeds
formally with formation of an Fe-C bond via a SN2-
like mechanism. Therefore, inversion of the absolute
configuration from (S) in the enantiopure starting
material to (R) occurs since the O and the Fe atom
possess the same relative ranking of Cahn-Ingold-
Prelog priority. For this reason, allyl complex 18′ with
a syn-Me,syn-SO2Ph substitution pattern can be as-
signed the (1R,2S,3R) configuration. As explained above,
it is sufficient to give only two stereochemical descrip-
tors for the complexed allylic carbon atoms, e.g., 18′ t
syn-Me,syn-SO2Ph-18 t (1R,2S,3R)-18 t (1R,3R)-18,
(53) For an example of an anionic (η3-allyl)tricarbonyl(1-) com-
plex: Chang, S.; Yoon, J .; Brookhart, M, J . Am. Chem. Soc. 1994, 116,
1869.
(54) A˙ kermark, B.; Krakenberger, B.; Hansson, S. Organometallics
1987, 6, 620.
(55) (a) Bonafoux, D.; Bordeau, M.; Biran, C.; Cazeau, P.; Dunogues,
J . J . Org. Chem. 1996, 61, 5532. (b) Emde, H.; Go¨tz, A.; Hofmann, K.;
Simchen, G. Liebigs Ann. Chem. 1981, 1643. (c) Ref 21f. (d) Revis, A.;
Hilty, T. K. J . Org. Chem. 1990, 55, 2972. (e) Ainsworth, C.; Chen, F.;
Kuo, Y.-N. J . Organomet. Chem. 1972, 46, 59.

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4325
Sch em e 6. Syn th esis of th e 3-Su bstitu ted Alk en yl Su lfon e (R)-23 a n d th e Ester (S)-24 by Ad d ition of Silyl
En ol Eth er 20 a n d Silyl Keten e Aceta l 21 to Com p lexes 18 a n d 19a
a
Reagents and conditions: (a) 1.0 equiv of 18′/′′ or 19′/′′, CH2Cl2, 3.0 equiv of 20 or 21, -78 °C to room temp, 12 h; (b) 4.0 equiv
of aqueous (NH4)2Ce(NO3)4 (CAN, 22), 0 °C to room temp, 8 h.
Sch em e 7. Syn th esis of (-)-(S)-Myop or on [(S)-28]
fr om th e Alk en yl Su lfon e (R)-2321f a
tion at C(3) accompanied by simultaneous cleavage of
the formal C-Fe bond. Attempts to isolate the inter-
mediately formed neutral C(3)-substituted (η2-alkene)-
tetracarbonyliron(0) complexes and to investigate their
stereochemistry failed. It seems plausible that they
possess the same relative and therefore absolute ster-
eochemistry with respect to the Fe(CO)4 moiety and C(3)
as described for the olefin complexes 14a -f, 15.
The enantiomeric excesses of compounds 23 obtained
(Table 5, entries 1-3) were determined by HPLC
employing a chiral stationary phase (Daicel OD) and by
comparison with the racemic material rac-23 (Table 5,
entry 4) obtained from nucleophilic addition of nucleo-
phile 20 to a complex mixture of rac-18′/′′ (Figure 8a).
Diastereo- and enantiomerically pure complex 18′ yields
(R)-23 in quantitative yield and in virtually enantiopure
form (ee > 99) (Figure 8c), while complex mixtures
containing 18′/′′ and ent-18′ give rise to alkenyl sulfone
23 with lower enantiomeric excesses (ee ) 66 and 59%,
respectively) (Figure 8b).
The determination of the enantiomeric excess and the
absolute configuration [(S)] of ester 24 was easily
accomplished by comparison of its optical rotation with
the optical rotation for compound (S)-24 reported in the
24
literature: [R]D -51.3 (c 2.98, CHCl3), ee > 96% vs
24
[R]D -48.2 (c 2.58, CHCl3), ee > 96%.21b
The enantiopure building block (R)-23 was previously
used in the stereocontrolled synthesis of the naturally
occurring hepatotoxic furanosequiterpenoid (-)-(S)-
myoporon, which allowed for an unambiguous determi-
nation of its absolute configuration.21f Palladium-
catalyzed hydrogenation of the alkenyl sulfone (R)-23
and subsequent protection of the keto functionality as
a dioxolane derivative furnished the saturated protected
sulfone (R)-25 in quantitative yield and without race-
mization (ee > 99%). The â-ketosulfone (R/S,R)-27 was
synthesized in 89% overall yield in a two-step procedure
by aldol-type addition of furan-3-carboxaldehyde (26) to
the R-lithio derivative of (R)-25 followed by subsequent
Swern oxidation (de ) 23%). Simultaneous removal of
both the acetal protecting group and the sulfone group
of (R/S,R)-27 was accomplished by reaction with zinc
dust under acidic aqueous conditions and gave (-)-(S)-
myoporon (S)-28 in 93% yield (ee > 99%, HPLC on
a
Reagents and conditions: (a) cat. 10% Pd/C, EtOAc, 1 atm
H2, room temp, 3 h (quant); (b) 5.0 equiv of (Me)3SiOCH2CH2-
OSi(Me)3, cat. (Me)3SiOTf, CH2Cl2, reflux, 5 days (quant.); (c)
(i) 1.2 equiv of n-BuLi, THF, -30 °C, 1 h; (ii) 2.0 equiv of furan-
3-carboxaldehyde (26), -78 °C to room temp, 5 h; (d) Swern-
oxidation (2 steps 89%); (e) 50 equiv of Zn-dust, EtOAc/HOAc/
THF (3:1:1), few drops of H2O, reflux, 12 h (93%).
The reactions proceeded with complete γ-regioselec-
tivity with respect to the electron acceptor group [at
C(3)] and with conservation of the (E)-double bond
geometry. Due to the overriding anti-directing effect of
the Fe(CO)4 fragment, the nucleophilic attack occurs
from the opposite side with respect to the Fe(CO)4
moiety (anti).1-3 During the addition step, a new
carbon-carbon bond is formed inverting the configura-
26
chiral Daicel OD phase) {[R]D -7.0 (c 1.39, MeOH) vs

4326 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
Ta ble 5. Nu cleop h ilic Ad d ition of Nu cleop h iles 20 a n d 21 to Com p lexes 18′/′′ a n d 19′/′′ F u r n ish in g Ad d ition
P r od u cts (R)-23 a n d (S)-24
RT
entry
complexes 18′/′′, 19′/′′a
syn-Me/anti-Meb
nucleophilec
R1
R2
product
yield [%]d
ee [%]e
[R]D (c, CHCl3)
1
2
3
4
5
18′
>99:1
>99:1
1:1.36
2.94:1
1:1.19
20
20
20
20
21
H
H
H
H
i-Bu
i-Bu
i-Bu
i-Bu
OMe
(R)-23
23
23
rac-23
(S)-24
quant.
76
quant.
quant.
82
>99
66
59
-4.7 (1.07)
18′/′′, ent-18′
18′/′′, ent-18′
rac-18′/′′
19′/′′
-2.1 (1.26)
f
0
0
Me
>96g
-51.3 (2.98)g
Complex mixtures were used except for entry 1. bsyn-Me/anti-Me ratio of complexes 18 and 19 determined by 1H NMR spectroscopy
a
c
(300/500 MHz, d3-nitromethane). See Table 3 for details. Silyl enol ether 20 and silyl ketene acetal 21 were prepared from their
corresponding carbonyl precursors and trimethylchlorosilane. dYield of analytically and spectroscopically pure material after purification
e
by column chromatography on silica gel. Unless otherwise stated, enantiomeric excesses determined by HPLC using a chiral Daicel OD
f
stationary phase in comparison with racemic material. Not determined. gDetermination of enantiomeric excess and absolute configuration
24
by comparison of the optical rotation with the optical rotation reported in the literature: [R]D -48.2 (c 2.58, CHCl3), ee > 96%).21b
F igu r e 8. Determination of the enantiomeric excesses of alkenyl sulfone 23 by HPLC using a chiral stationary phase in
comparison with racemic material rac-23; Conditions: Daicel OD, i-PrOH/cyclohexane ) 2:98, flow 0.5 mL min-1. (a) See
Table 5, entry 4; (b) see Table 5, entry 3; (c) see Table 5, entry 1.
25
[R]D -8.5 (c 1.54, MeOH)}.21f,56 Using enantiopure
complexes 18′ or 19′/′′, several other natural products
such as pheromones in their absolute natural configura-
tions were synthesized, further supporting the stereo-
chemical conclusions drawn from this study.21d-f,i
sion of the absolute stereochemistry at C(3) with respect
to the starting material. For the following discussions
it will be assumed that the soft test nucleophiles 20 and
21 invariably approach the complexes anti with respect
to the shielding Fe(CO)4 moiety. Thus, addition of
nucleophile 20 to complex 18′ afforded after oxidative
workup alkenyl sulfone (R)-23 in quantitative yield and
in enantiopure form (ee > 99%) (Table 5, entry 1). The
overall reaction from (S)-6a via 18′ to (R)-23 proceeded
with virtually complete self-reproduction of chirality
(chirality transfer) from C(3)-O [in (S)-6a ] (central
chirality) to C(3)-Fe (formally planar chirality) [in
(1R,2S,3R)-18] to C(3)-C [in (R)-23] (central chirality)
and with retention (double inversion) of the stereogenic
center with respect to the starting material.
Mixtures of complexes 14a ′/a ′′ (de ) 42, 30, or 75%)
result in the formation of complex mixtures 18′/′′ and
ent-18′ albeit in lower isolated yield (Table 3, entries
2-4). These mixtures exhibit by 1H NMR spectroscopic
analysis a syn-Me/anti-Me ratio of > 99:1 (de ) 99%)
(Table 3, entries 2 and 3) or 1:1.36 (de ) 15%) (Table 3,
entry 4), which deviate remarkably from theoretically
calculated ratios. Each diastereomer, 14a ′ or 14a ′′,
respectively, supposedly reacts stereospecifically to yield
Mech a n istic Discu ssion a n d Con clu sion
The diastereo- and enantiomerically pure (η2-alkene)-
tetracarbonyliron(0) complex 14a′ [(1R,2S,3S)-14a, Ψ-exo-
14a ] (de ) ee > 99%) was quantitatively transformed
into the corresponding syn-Me,syn-SO2Ph-configured
(η3-allyl)tetracarbonyliron(1+) complex 18′ [(1R,2S,3R)-
18]. The reaction proceeds without any detectable
isomerization or epimerization processes, thus retaining
the overall “W”-shaped geometry of the allylic ligand
(syn-Me/anti-Me > 99:1, de ) ee > 99%) (Table 3, entry
1). The relative Ψ-exo-arrangement of the OPG leaving
group unit and the Fe(CO)4 moiety (anti to each other)
in 14a ′ facilitates this transformation, which proceeds
with the formal formation of an Fe-C bond and inver-
(56) (a) Burka, L. T.; Iles, J . Phytochemistry 1979, 18, 873. (b) Burka,
L. T.; Kahnert, L.; Wilson, B. J .; Harris, T. M. J . Am. Chem. Soc. 1977,
99, 2302. (c) Oba, K.; Uritani, I. Plant Cell Physiol. 1979, 20, 819.

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4327
the diastereomeric complexes 18′ (syn-Me,syn-SO2Ph-
18) (from 14a ′ or Ψ-exo-14a ) and 18′′ (anti-Me,syn-SO2-
Ph-18) (from 14a ′′ or Ψ-endo-14a ) with formal formation
of an Fe-C bond and inversion of the absolute stereo-
chemistry at C(3). Thus, in the absence of isomerization
processes, each of them should be obtained in enantio-
merically pure form and should react with nucleophile
20 to give alkenyl sulfone (R)-23 in high enantiomeric
purity. Complex 14a ′ in a mixture consisting of 14a ′ and
14a ′′ reacts supposedly quantitatively and stereospe-
cifically to give complex 18′ (de ) ee > 99%). Conversion
of complex 14a ′′ (in a mixture of 14a ′/a ′′) to complex
18′′ must be obviously incomplete and must be as well
subject to an undetermined degree of an isomerization
into a thermodynamically more stable syn-Me,syn-SO2-
Ph-configured complex. Complex 14a ′′ [(1S,2R,3S)-14a ]
reacts from the Ψ-endo-conformation to form complex
18′′ [(1S,2R,3R)-18, anti-Me,syn-SO2Ph-18]. This re-
quires that 14a ′′ arranges its OPG leaving group unit
anti to the Fe(CO)4 moiety prior to acidic cleavage to
yield the “S”-shaped allylic backbone (t anti-Me,syn-
SO2Ph) of 18′′. Low relative yields and anti-Me to syn-
Me isomerization processes for transformations of re-
lated Ψ-endo-(η4-diene)tricarbonyliron(0) complexes into
their corresponding (η5-pentadienyl)tricarbonyliron(1+)
were also previously reported in the literature.57
The anti-Me to syn-Me isomerization may proceed via
one of the possible pathways discussed in Figure 6. A
π-σ-π isomerization would result in net retention of
absolute stereochemistry at C(3) [(1S,2R,3R)-18 (18′′)
f (1R,2S,3R)-18 (18′)] including a change of topicity of
the Fe(CO)4 group with respect to the allylic plane. An
anti-Me to syn-Me isomerization involving conservation
of topicity of the Fe(CO)4 group with respect to the
allylic plane would as well result in the formation of a
thermodynamically favored syn-Me,syn-SO2Ph-con-
figured allyl complex but involving an inversion of
absolute configuration only at C(3) [(1S,2R,3R)-18 (18′′)
f [(1S,2R,3S)-18 (ent-18′)]. This analysis means that
all complexes 18 with a syn-Me,syn-SO2Ph configuration
comprising a mixture 18′ (from 14a ′) and ent-18′ (from
14a ′′) would have an overall lowered enantiomeric
excess, while the remaining complex anti-Me,syn-SO2-
Ph complex 18′′ should be enantiopure.
18′/′′, including 14f′/f′′ (Table 3, entries 5 and 6).
Addition of nucleopile 20 to a mixture of 18′/′′ and ent-
18′ derived from a mixture of precursors 14f′/f′′ yielded
alkenyl sulfone 23 with low enantiomeric excess.58
Identical stereochemical considerations allow for a
discussion of the stereochemistry of the formation of a
complex mixture 19′/′′ from a mixture of precursor
complexes 15′/′′ (de ) 12-16% or 10%, respectively)
(Table 3, entries 7 and 8). The observed diastereomeric
excesses are basically retained in complexes 19 (de )
12-16% or 9%; syn-Me/anti-Me ratio ) 1:1.30 or 1:1.19).
On the basis of the excellent mass balance (>95%), it
seems reasonable that in this case complexes Ψ-exo-15
[15′′, (1S,2R,3S)-15] and Ψ-endo-15 [15′, (1R,2S,3S)-15]
react with similar efficiency and stereospecifically to
give the corresponding (η3-allyl)tetracarbonyliron(1+)
complexes 19′′ [(1S,2R,3R)-19, syn-Me,syn-CO2Me-19]
and 19′ ((1R,2S,3R)-19, anti-Me,syn-CO2Me-19]. The
lack of any detectable anti-Me f syn-Me isomerization
1
(according to H NMR spectroscopy) suggests that the
diastereomers 19′ and 19′′ are obviously configuration-
ally stable and each of them is present in highly
enantiomerically enriched form. Assuming a uniform
anti-addition mechanism and that syn-Me,syn-CO2Me-
19 [(1S,2R,3R)-19,19′′] and anti-Me,syn-CO2Me-19
[(1R,2S,3R)-19, 19′] exhibit similar reactivity toward the
soft nucleophile 21, one would expect to isolate ester
24 in high yield and in enantiopure form. In fact, the
unsaturated ester (S)-24 was obtained in 82% yield and
in virtually enantiopure form (ee > 96%) (Table 5, entry
5). The overall reaction from (S)-8 via 19′/′′ to (S)-24
must again have proceeded with virtually complete self-
reproduction of chirality (chirality transfer) and there-
fore with retention (double inversion) of the stereogenic
center with respect to the starting material. Our results
are in close accordance for numerous transition metal
catalyzed or mediated allylic substitution reactions
which were reported to proceed with overall retention
of absolute configuration (double inversion), although
mechanisms with double retention are discussed as well
in the literature.4,6-9,21,23,25,29 As of now, we cannot offer
a conclusive explanation why and how exactly the
nature of the substituents influences the configurational
stability of anti-configured methyl substituents.
Consequently, complexes 18′ [(1R,2S,3R)-18] and 18′′
[(1S,2R,3R)-18] react with nucleophile 20 to give alkenyl
sulfone (R)-23 with the same absolute configuration.
Addition of nucleophile 20 to complex ent-18′ [(1S,2R,3S)-
18] yields the optical antipode (S)-23. Therefore, addi-
tion of nucleophile 20 to mixtures of 18′/′′ and ent-18′
(obtained from mixtures of precursor complexes 14a ′/
a ′′) must afford alkenyl sulfone 23 with lower enantio-
meric excess, as it has been experimentally demon-
strated (Table 5, entries 2 and 3, Figure 8) (ee ) 66 and
59%). In addition, there is no indication that complexes
18′ (syn-Me,syn-SO2Ph-18) and 18′′ (anti-Me,syn-SO2-
Ph-18) exhibit a different reactivity toward nucleophile
20 since the yields of material 23 obtained are quantita-
tive (Table 5, entries 3 and 4). The stereochemical
conclusions gained from the conversion of complexes
14a ′/a ′′ to 18′/′′ should be applicable for the transforma-
tion of all complexes of type 14 into complexes of type
In conclusion, we have delineated the mechanistic and
stereochemical pathways for the formation of diastereo-
and enantiomerically enriched olefinic and allylic tetra-
carbonyl iron complexes. These organometallics repre-
sent key intermediates in our iron-mediated allylic
substitution reactions with self-reproduction of chirality
(“chirality transfer”). Although this “chirality transfer
process” in allylic substitution reactions is of stoichio-
metric nature with respect to the (η3-allyl)tetra-
carbonyliron(1+) complexes employed, the high vari-
ability in substitution pattern of the allylic unit, the
broad range of nucleophiles employable, and the pos-
sibility of preparing easily both enantiomers of a highly
functionalized and stereochemically well-defined opti-
cally pure target molecule display the great synthetic
potential of this protocol. The methodology presented
should be regarded as a useful alternative for acylic
stereocontrol in comparison to catalytic variants of
(57) Enders, D.; J andeleit, B.; von Berg, S. J . Organomet. Chem.
1997, 533, 219.
(58) Enders, D.; J andeleit, B. University of Technology Aachen,
1995, unpublished results.

4328 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
phosphite (91%), and its oxidation to the sulfone (90%)
according to a literature procedure.35 Methyl diethyl phospho-
nato acetate (7) was synthesized in 93% yield from triethyl
phosphite and methyl bromoacetate by Michaelis-Arbuzov
rearrangement.36 Alkene (S)-8 can now also be purchased from
ACROS Chimica, Belgium.37 Nonacarbonyldiiron (13) was
photochemically synthesized by irradiation of pentacarbonyl-
iron in a mixture of glacial acetic acid/acetic acid anhydride
using a Philips HPK 125 W or TQ 150 W medium-pressure
mercury lamp and a Dema irradiation apparatus.41 Silyl enol
ether 20 and silyl ketene acetal 21 were prepared from their
corresponding carbonyl precursors and trimethylchlorosilane
via the lithium enolates according to literature procedures.55
The nucleophiles 20 and 21 were stored and handled with
exclusion of moisture and air.
allylic substitution reactions, which are often limited
in their range of nucleophilic components and allylic
substrates. The mechanistic insight and understanding
thus obtained allow for a rational extension of this
methodology. A general use of these planar chiral iron
complexes as synthetic equivalents of a4-synthons for
homologous (1,5) conjugate addition reactions is of
interest both as a form of Umpolung of classical d4-
chemistry and as a method of considerable synthetic
potential.30
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were carried out
under an atmosphere of dry argon or carbon monoxide using
standard Schlenk or vacuum line techniques unless otherwise
stated. Solvents were dried and purified by conventional
methods prior to use. Diethyl ether (Et2O) was freshly distilled
from sodium benzophenone ketyl, and ethanol-free dichlo-
romethane (CH2Cl2), acetonitrile, n-pentane, and n-hexane
were distilled from calcium hydride under an atmosphere of
argon. Toluene was distilled from molten sodium under an
atmosphere of argon. Light petroleum refers to the fraction
with bp 40-80 °C. Reagents of commercial quality were
obtained from commercial suppliers and were used from
freshly opened containers without further purification unless
otherwise stated.
Sa fety n ote: Most reactions with compounds containing
the iron carbonyl moiety lead to variable amounts of iron
carbonyl, especially pentacarbonyl iron. These compounds are
volatile and presumably toxic and must be handled with
utmost care. They can be oxidatively decomposed with either
KOH/H2O2, diluted HNO3, or Br2/H2O.
Tetr a ca r bon yl[(1-2η)-(E,1R,2S,3S)-3-p h en ylm eth oxy-
1-(p h en ylsu lfon yl)bu t-1-en ]ir on (0) [(1R,2S,3S)-14a , 14a ′,
ψ-exo-14a ] a n d Tet r a ca r b on yl[(1-2η)-(E,1S,2R,3S)-3-
p h e n ylm e t h oxy-1-(p h e n ylsu lfon yl)b u t -1-e n e ]ir on (0)
[(1S,2R,3S)-14a , 14a ′′, ψ-en d o-14a ]. Representative proce-
dure: 3.03 g (10.0 mmol) of alkenyl sulfone (S)-6a and 4.73 g
(13.0 mmol) of nonacarbonyldiiron [Fe2(CO)9] (13) were placed
in a 250 mL Schlenk flask and were suspended in anhydrous
n-hexane (150 mL).21g,42 The reaction mixture was stirred at
room temperature for 3 days under an atmosphere of carbon
monoxide and with exclusion of sunlight. After dilution with
anhydrous diethyl ether (100 mL), filtration over Celite/sea
sand, and washings with anhydrous diethyl ether a clear
yellow filtrate was obtained. Removal of the solvents under
reduced pressure, filtration of an ether solution (anhydrous
diethyl ether) of the crude reaction product under argon by
means of a PTFE-syringe filter device (pore size, 0.45 µm), and
evaporation to dryness in a Schlenk flask yielded 4.70 g
(quant.) of a yellowish solid, which was obtained in spectro-
scopic and analytical pure form. In general, a crude mixture
of olefinic tetracarbonyliron complexes can be further purified
by inert gas column chromatography (collection of the yellow
fraction) employing previously dried and degassed silica gel
and degassed and argon-saturated solvents (light petroleum/
diethyl ether mixtures as indicated), which may lead to a slight
enrichment of one of the diastereomers. Diastereo- and enan-
tiomerically pure complex (1R,2S,3S)-14a (14a ′, Ψ-exo-14a )
(de ) ee > 99%) was obtained after the first filtration by
fractional crystallization from the partly evaporated filtrate
(n-hexane/diethyl ether mixture) at -25 °C in a freezer to
furnish 1.88-3.06 g (40-64%) of a bright yellow solid or
crystals. Small amounts of highly diastereo- and enantiomeri-
cally enriched minor diastereomer (1S,2R,3S)-14a (14a ′′,
Ψ-endo-14a ) (de ) ee > 99%) were obtained by fractional
crystallization from remaining concentrated mother liquors.
Screening of the different reaction conditions for complexation
of ligand (S)-6a (solvent, temperature) was operationally
identically performed. (1R,2S,3S)-14a mp 103 °C, dec;
1S,2R,3S)-14a mp 110 °C, dec. Rf: 0.43 (light petroleum/
diethyl ether ) 2:1). de ) 70% (crude), de ) ee > 99% (after
fractional crystallization determined by 1H NMR spectroscopy,
Analytical precoated glass-backed TLC plates (silica gel 60
F
254) and silica gel 60 (230-400 mesh, i.e., particle size 0.040-
0.063 mm) were purchased from Merck, Darmstadt, Germany.
Melting points are uncorrected and were measured on a Dr.
Tottoli apparatus. Analytical GLC was performed on Siemens
Sichromat 2 and 3 equipped with an SE-54-CB or an OV-1-
CB column (both 25 m × 0.25 mm), carrier gas: nitrogen, FID.
Optical rotations were measured using a Perkin-Elmer P 241
polarimeter and chloroform of Merck UVASOL quality. Ana-
lytical HPLC for the determination of enantiomeric purities
was conducted on a Hewlett-Packard 1050 equipped with
chiral stationary phase (Daicel OD), UV-detector. Preparative
HPLC was performed on Gilson Abimed; Merck-LiCrosorb-
column (25 cm × 25 mm, silica 60, particle size 0.007 mm),
UV-detector. 1H NMR (500/300 MHz) and 13C NMR (125/75
MHz) spectroscopy were conducted on a Varian Unity 500 and
a Varian VXR 300 spectrometer using tetramethylsilane (TMS)
as internal standard. Resonances in the 1H NMR spectra of
compounds containing the phenylsulfonyl group are indicated
as ortho-, meta-, or para-C-H. Resonances in the 13C NMR
spectra of compounds containing the phenylsulfonyl group are
indicated as ortho-, meta-, or para-C. IR spectra (film on NaCl,
KBr) were recorded on a Perkin-Elmer FT/IR 1750 spectro-
photometer. Mass spectra were measured on a Varian MAT
212 (EI 70 eV, 1 mA). Microanalyses were obtained with a
Herae¨us CHN-O-RAPID elemental analyzer. High-resolution
mass spectra were performed on a Finnigan MAT 95.
O-Benzyl-2,2,2-trichloroacetimidate was synthesized by so-
dium hydride-catalyzed addition of benzyl alcohol to trichlo-
roacetonitrile and was used without further purification.59
Aliquots of commercially available solutions of Red-Al (Red-
Al: sodium bis(2-methoxyethoxy)aluminum hydride) in tolu-
ene (ca. 3.5 mol L-1) were diluted with anhydrous toluene to
a concentration of ca. 0.5-1.5 mol L-1) prior to use. Diethyl
(phenylsulfonyl)methylphosphonate (5) was prepared in 59%
overall yield from thiophenol by successive chloromethylation
with paraformaldehydehydrochloric acid (73%), Michaelis-
Arbuzov rearrangement of the resulting thiophenyl chloro
methyl ether to the corresponding phosphonate with triethyl
26
500 MHz, signals: CHCH3, ortho-C-H). (1R,2S,3S)-14a : [R]D
26
+171.8 (c 1.05, C6H6). (1S,2R,3S)-14a : [R]D +198.5 (c 0.46,
C6H6). NMR spectroscopic data for the major diastereomer
(1R,2S,3S)-14a (14a ′, Ψ-exo-14a ): 1H NMR (500 MHz, C6D6)
δ 0.91 (d, 3H, J ) 6.1 Hz, CHCH3), 3.04 (qdd, 1H, J ) 6.1, 5.8,
0.3 Hz, CHCH3), 3.29 (dd, 1H, J ) 10.4, 5.8 Hz, CHdCHSO2),
3.79 (d, 1H, J ) 12.1 Hz, OCHHC6H5), 3.86 (dd, 1H, J ) 10.2,
0.3 Hz, CHdCHSO2), 3.93 (d, 1H, J ) 12.1 Hz, OCHHC6H5),
6.87-7.13 (m, superimposed, 8H, OCH2C6H5, meta-, -para-C-
(59) (a) Wessel, H.-P.; Iversen, T.; Bundle, D. R. J . Chem. Soc.,
Perkin Trans. 1 1985, 2247. (b) Iversen, T.; Bundle, D. R. J . Chem.
Soc., Chem. Commun. 1981, 1240. (c) Ainsworth, C.; Chen, F.; Kuo,
Y.-N. J . Organomet. Chem. 1972, 46, 59.

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4329
H), 7.85-7.91 (m, 2H, ortho-C-H) ppm; 13C NMR (125 MHz,
C6D6) δ 21.73 (CHCH3), 57.96 (CHdCHSO2), 66.70 (CHd
CHSO2), 70.15 (OCH2), 76.31 (CHCH3), 127.84 (ortho-C,
superimposed with C6D6), 128.04, 128.23, 128.47 (OCH2C6H5),
129.13 (meta-C), 132.54 (para-C), 137.97 (ipso-OCH2C6H5),
142.66 (ipso-C), 207.25 (br, superimposed with major diaste-
reomer, Fe-CO) ppm. NMR spectroscopic data for the minor
diastereomer (1S,2R,3S)-14a (14a ′′, Ψ-endo-14a ): 1H NMR
(500 MHz, C6D6) δ 0.86 (d, 3H, J ) 6.1 Hz, CHCH3), 3.11 (qd,
br., 1H, J ) 6.1, 5.5 Hz, CHCH3), 3.29 (dd, 1H, J ) 10.4, 5.2
Hz, CHdCHSO2), 3.76 (d, 1H, J ) 10.4 Hz, CHdCHSO2), 3.83
(d, 1H, J ) 11.9 Hz, OCHHC6H5), 4.12 (d, 1H, J ) 11.9 Hz,
OCHHC6H5), 6.87-7.13 (m, superimposed, 8H, OCH2C6H5,
meta-, para-C-H), 7.80-7.84 (m, 2H, ortho-C-H) ppm; 13C
NMR (125 MHz, C6D6) δ 21.86 (CHCH3), 59.23 (CHdCHSO2),
65.52 (CHdCHSO2), 70.07 (OCH2), 74.52 (CHCH3), 127.45
(ortho-C), 127.94, 128.32, 128.53 (OCH2C6H5), 129.24 (meta-
C), 132.43 (para-C), 137.97 (ipso-OCH2C6H5), 143.23 (ipso-C,
superimposed with major diastereomer), 207.25 (br, superim-
posed with major diastereomer, Fe-CO) ppm. All additional
spectroscopic and analytical data correspond with those re-
ported in the literature.21g,42
SdO), 1262 (s), 1165 (w), 1145 (s, SdO), 1084 (s, C-O-C),
1039, 1026 (s, br, C-O-C), 927 (w), 628 (vs), 591, 566 (m)
cm-1; MS (70 eV) m/z (relative intensity) 416 (6) [M•+ - 3CO],
389 (15), 388 (56) [M•+ - 4CO], 359 (18), 358 (77) [M•+
-
SO2C6H5], 268 (15), 267 (100) [388 - CH2OCH2C6H5], 250 (16),
239 (15), 196 (7), 161 (14), 143 (7) [H2SO2C6H5+], 134 (8), 133
(37), 112 (8), 107 (5) [C7H8O+], 91 (61) [C7H7+], 84 (19), 77 (14)
[C6H5+], 65 (12) [C5H5+], 56 (53) [Fe+], 55 (10), 53 (11) [C4H3+],
51 (10), 45 (10), 43 (13), 41 (12). Anal. Calcd for C22H20FeSO8
(Mr 500.30): C, 52.82; H, 4.03. Found: C, 52.69; H 4.37.
Te t r a ca r b on yl[(1-2η)-(E ,1R ,2S ,3S )-3-(t er t -b u t yld i-
m e t h y ls ilo x y )-1-(p h e n y ls u lfo n -y l)b u t -1-e n e ]ir o n (0)
[(1R,2S,3S)-14c, 14c′, Ψ-exo-14c] a n d Tetr a ca r bon yl[(1-
2η)-(E,1S,2R,3S)-3-(ter t-bu tyld im eth ylsiloxy)-1-(p h en yl-
su lfon yl)bu t-1-en e]ir on (0) [(1S,2R,3S)-14c, 14c′′, ψ-en d o-
14c]. By analogy with the procedure for 14a ′/a ′′, 1.47 g (4.50
mmol) of alkenyl sulfone (S)-6c was reacted with Fe2(CO)9 (13)
(2.13 g, 5.85 mmol) in anhydrous diethyl ether (50 mL) to yield
2.00 g (90%) of a yellow viscous oil after purification by inert
gas column chromatography (silica gel, light petroleum/diethyl
ether ) 4:1) and filtration by a PTFE-filter.21g,42 Rf: 0.53 and
0.43 (light petroleum/diethyl ether ) 2:1). de: 15-16% (after
purification by inert gas column chromatography determined
by 1H NMR spectroscopy, 300 MHz, signals: CHdCHSO2,
CHCH3, C(CH3)3, Si(CH3)2. NMR spectroscopic data for the
major diastereomer (1R,2S,3S)-14c (14c′, Ψ-exo-14c): 1H NMR
(300 MHz, C6D6) δ -0.38 (s, 3H, SiCH3), -0.21 (s, 3H, SiCH3),
0.71 (s, 9H, C(CH3)3), 1.07 (d, 3H, J ) 5.8 Hz, CHCH3), 3.33-
3.45 (m, 2H, CHCH3, CHdCHSO2), 3.78 (d, 1H, J ) 9.9 Hz,
CHdCHSO2), 6.96-7.04 (m, superimposed with minor di-
astereomer, 3H, meta-, para-C-H), 7.85-7.93 (m, superim-
posed with minor diastereomer, 2H, ortho-C-H) ppm; 13C
NMR (75 MHz, C6D6) δ -4.83 (SiCH3), -4.17 (SiCH3), 18.24
(C(CH3)3), 25.83 (C(CH3)3), 26.06 (CHCH3), 60.09 (CHdCHSO2),
68.00 (CHdCHSO2), 73.04 (CHCH3), 127.99 (ortho-C), 129.24
(meta-C), 132.57 (para-C), 142.36 (ipso-C), 207.19 br, super-
imposed with minor diastereomer, Fe-CO) ppm. NMR spec-
troscopic data for the minor diastereomer (1S,2R,3S)-14c
(14c′′, Ψ-endo-14c): 1H NMR (300 MHz, C6D6) δ -0.41 (s, 3H,
SiCH3), -0.33 (s, 3H, Si(CH3), 0.65 [s, 9H, C(CH3)3], 0.96 (d,
3H, J ) 6.1 Hz, CHCH3), 3.50 (dd, 1H, J ) 10.2, 3.8 Hz,
CHdCHSO2), 3.84 (d, 1H, J ) 10.2 Hz, CHdCHSO2), 4.00 (qd,
1H, J ) 5.8, 3.8 Hz, CHCH3), 6.96-7.04 (m, superimposed with
major diastereomer, 3H, meta-, para-C-H), 7.85-7.93 (m,
superimposed with major diastereomer, 2H, ortho-C-H) ppm;
13C NMR (75 MHz, C6D6) δ -5.19 (SiCH3), -5.02 (SiCH3),
18.24 (C(CH3)3), 25.79 (C(CH3)3), 27.29 (CHCH3), 62.89
(CHdCHSO2), 64.89 (CHdCHSO2), 68.63 (CHCH3), 127.55
(ortho-C), 129.30 (meta-C), 132.48 (para-C), 143.34 (ipso-C),
207.19 (br, superimposed with major diastereomer, Fe-CO)
ppm. IR (KBr): ν 2955, 2931, 2896, 2858 (w, CH, CH3), 2107
(vs, axial-Fe-CO), 2061, 2042, 2028, 2000 (vs, Fe-CO), 1471,
1463 (vw, Ar-CdC), 1448 (m), 1385 (s, CH3), 1319, 1304 (s,
SdO), 1254 (m), 1145, (s, SdO), 1121(s, C-O-Si), 1084, 1036,
992, 963, 880, 837, 804, 777, 754, 710, 688 (m), 630 (s), 585,
565 (m) cm-1; MS (70 eV) m/z (relative intesity) 494 (0.5) [M•+],
466 (6) [M•+ - CO], 438 (4) [M•+ - 2CO], 411 (11), 410 (32)
[M•+ - 3CO], 384 (12), 383 (27) [438 - C4H9], 382 (100) [M•+
- 4CO], 325 (7) [382-C4H9], 314 (33), 299 (22), 271 (28), 257
(16), 250 (27), 243 (24), 239 (20), 208 (11), 207 (69) 145 (10),
143 (1) [H2SO2C6H5+], 133 (13), 131 (17), 130 (10), 127 (12),
115 (2) [OSi(CH3)2C(CH3)3+], 91 (5), 77 (5) [C6H5+], 75 (24)
[HOdSi(CH3)2+], 73 (17), 57 (1) [C4H9+], 56 (15) [Fe+]. Anal.
Calcd for C20H26FeSSiO7 (Mr 494.41): C, 48.59; H, 5.30.
Found: C, 48.56; H 5.33.
Tet r a ca r b on yl[(1-2η)-(E,1R,3S)-3-(p h en ylm et h oxy)-
m eth oxy-1-(ph en ylsu lfon yl)-bu t-1-en e]ir on (0) [(1R,2S,3S)-
14b, 14b′, Ψ-exo-14b] an d Tetr acar bon yl[(1-2η)-(E,1R,3S)-
3-(p h e n ylm e t h oxy)m e t h oxy-1-(p h e n ylsu lfon yl)b u t -1-
en e]ir on (0) [(1S,2R,3S)-14b, 14b′′, ψ-en d o-14b]. By analogy
to the procedure for 14a ′/a ′′, 838 mg (2.50 mmol) of alkenyl
sulfone (S)-6b was reacted with Fe2(CO)9 (13) (1.164 g, 3.20
mmol) in anhydrous diethyl ether or n-hexane (40 mL) to yield
900 mg (72%) of an orange-colored viscous oil after purification
by inert gas column chromatography (silica gel, light petroleum/
diethyl ether ) 4:1).21g,42 Rf: 0.13 (light petroleum/diethyl ether
) 4:1). de: 18% (after purification by inert gas column
chromatography determined by 1H NMR spectroscopy, 300
MHz, signals CHCH3, CHdCHSO2). NMR spectroscopic data
for the major diastereomer (1R,2S,3S)-14b (14b′, Ψ-exo-14b):
1H NMR (300 MHz, C6D6) δ 0.95 (d, 3H, J ) 6.1 Hz, CHCH3),
3.27 (dd, 1H, J ) 10.6, 5.5 Hz, CH)CHSO2), 3.44 (quint., br,
1H, J ≈ 6.0 Hz, CHCH3), 3.84 (d, 1H, J ) 10.2 Hz,
CHdCHSO2), 4.08-4.17 (m, superimposed with minor diastereo-
mer, 2H, OCH2C6H5), 4.30 (d, 1H, J ) 7.1 Hz, OCHHO), 4.34
(d, 1H, J ) 6.9 Hz, OCHHO), 6.89-7.15 (m, superimposed with
minor diastereomer, 8H, OCH2C6H5, meta-, para-C-H), 7.81-
7.91 (m, superimposed with minor diastereomer, 2H, ortho-
C-H) ppm; 13C NMR (75 MHz, C6D6) δ 22.38 (CHCH3), 57.60
(CHdCHSO2), 66.50 (CHdCHSO2), 69.49 (OCH2C6H5), 74.73
(CHCH3), 92.22 (OCH2O), 127.34, 127.84, 128.54, 129.11
(ortho-C, OCH2C6H5, superimposed with minor diastereomer
and C6D6), 129.17 (meta-C), 132.59 (para-C), 138.15 (ipso-
OCH2C6H5), 142.49 (ipso-C), 207.08 (br, superimposed with
major diastereomer, Fe-CO) ppm. NMR spectroscopic data for
the minor diastereomer (1S,2R,3S)-14b (14b′′, Ψ-endo-14b):
1H NMR (300 MHz, C6D6) δ 0.90 (d, 3H, J ) 6.1 Hz, CHCH3),
3.35 (dd, 1H, J ) 10.6 Hz, 5.0 Hz, CHdCHSO2), 3.58 (quint.,
br, 1H, J ) 5.6 Hz, CHCH3), 3.79 (d, 1H, J ) 10.6 Hz,
CHdCHSO2), 4.08-4.17 (m, superimposed with major diastereo-
mer, 2H, OCH2C6H5), 4.19 (d, 1H, J ) 6.5 Hz, OCHHO), 4.23
(d, 1H, J ) 6.9 Hz, OCHHO), 6.89-7.15 (m, superimposed with
major diastereomer, 8H, OCH2C6H5, meta-, para-C-H), 7.81-
7.91 (m, superimposed with major diastereomer, 2H, ortho-
C-H) ppm; 13C NMR (125 MHz, C6D6) δ 22.69 (CHCH3), 59.48
(CHdCHSO2), 65.22 (CHdCHSO2), 69.49 (OCH2C6H5), 73.18
(CHCH3), 91.99 (OCH2O), 127.79, 127.84, 128.54, 129.11
(ortho-C, OCH2C6H5, superimposed with major diastereomer
and C6D6), 129.25 (meta-C), 132.54 (para-C), 137.98 (ipso-
OCH2C6H5), 143.01 (ipso-C), 207.08 (br, superimposed with
major diastereomer, Fe-CO) ppm; IR (film on NaCl) ν 3067
(w), 3056 (m), 3020 (w, Ar-C-H), 2964, 2933, 2894 (w, CH,
CH2, CH3), 2105 (vs, axial-Fe-CO), 2032, 2005 (vs, Fe-CO),
1498 (vw, CdC, Ar-CdC), 1448 (m), 1381 (w, CH3), 1304 (s,
Tet r a ca r b on yl[(1-2η)-(E,1R,2S,3S)-3-{(2-n a p h t h yl)-
m eth oxy}-1-(ph en ylsu lfon yl)bu t-1-en e]ir on (0) [(1R,2S,3S)-
14d,14d′,Ψ-exo-14d]and Tetracarbonyl[(1-2η)-(E,1S,2R,3S)-
3-{(2-naphthyl)methoxy}-1-(phenylsulfonyl)but-1-ene]iron(0)
[(1S,2R,3S)-14d , 14d ′′, ψ-en d o-14d ]. By analogy with the
procedure for 14a ′/a ′′, 1.06 g (3.00 mmol) of alkenyl sulfone

4330 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
(S)-6d was reacted with Fe2(CO)9 (13) (1.41 g, 3.90 mmol) in
anhydrous diethyl ether (45 mL) to yield 740 mg (48%) of a
beige-colored solid after purification by inert gas column
chromatography (silica gel, light petroleum/diethyl ether )
4:1).21g,42 Mp: 108 °C (dec). Rf: 0.17 (light petroleum/diethyl
ether ) 4:1). de: 45% (after purification by inert gas column
chromatography determined by 1H NMR spectroscopy, 300
MHz, CHCH3). NMR spectroscopic data for the major diaste-
reomer (1R,2S,3S)-14d (14d ′, Ψ-exo-14d ): 1H NMR (300 MHz,
C6D6) δ 0.94 (d, 3H, J ) 6.2 Hz, CHCH3), 3.10 (quint., br, 1H,
posed with C6D6), 129.17 (meta-C), 132.62 (para-C), 142.51
(ipso-C), 207.25 (br, superimposed with minor diastereomer,
Fe-CO) ppm. NMR spectroscopic data for the minor diaste-
reomer (1S,2R,3S)-14e (14e′′, Ψ-endo-14e): 1H NMR (300
MHz, C6D6) δ 0.82 (d, 3H, J ) 6.0 Hz, CHCH3), 1.58 (d, 1H, J
) 4.4 Hz, OH), 3.33 (dd, 1H, J ) 10.2, 6.0 Hz, CHdCHSO2),
3.37-3.46 (m, 1H, CHCH3), 3.69 (d, 1H, J ) 10.4 Hz, CHd
CHSO2), 6.93-7.05 (m, superimposed with major diastere-
omer, meta-, para-C-H), 7.79-7.89 (m, 2H, superimposed with
major diastereomer, ortho-C-H) ppm; 13C NMR (75 MHz,
C6D6) δ 26.07 (CHCH3), 61.35 (CHdCHSO2), 65.81 (CHd
CHSO2), 69.52 (CHCH3), 127.47 (ortho-C), 129.28 (meta-C),
133.43 (para-C), 142.96 (ipso-C), 207.25 (br, superimposed with
major diastereomer, Fe-CO) ppm; IR (film on NaCl) ν 3496
(w-m, br., OH), 3021 (w, Ar-C-H), 2970, 2927 (w, CH, CH3),
2104 (vs, axial-Fe-CO), 2030, 2001 (vs, Fe-CO), 1585, 1479
(vw, Ar-CdC), 1447 (m), 1369 (w, CH3), 1302 (s, SdO), 1217
(m), 1143 (s, SdO), 1084 (s), 808, 750, 719, 689 (m), 626 (s),
592 (w) cm-1; MS (70 eV) m/z (relative intesity) 380 (0.1) [M•+],
J
≈ 6.0 Hz, CHCH3), 3.32 (dd, 1H, J ) 10.2, 5.5 Hz,
CHdCHSO2), 3.92 (d, 1H, J ) 10.6 Hz, CHdCHSO2), 3.96 (d,
1H, J ) 12.3 Hz, OCHHC10H7), 4.09 (d, 1H, J ) 12.3 Hz,
OCHHC10H7), 6.83-7.93 (m, superimposed with minor di-
astereomer, 12H, OCH2C10H7, meta-, para-, ortho-C-H) ppm;
13C NMR (75 MHz, C6D6) δ 21.85 (CHCH3), 57.91 (CHdCHSO2),
66.69 (CHdCHSO2), 70.30 (OCH2), 76.44 (CHCH3), 126.04-
129.09 (OCH2C10H7, superimposed with minor diastereomer
and C6D6), 132.51 (para-C), 133.42-133.62 (OCH2C10H7),
135.39 (ipso-OCH2C10H7), 142.60 (ipso-C), 207.08 (br, super-
imposed with minor diastereomer, Fe-CO) ppm. NMR spec-
troscopic for the minor diastereomer (1S,2R,3S)-14d (14d ′′,
Ψ-endo-14d ): 1H NMR (300 MHz, C6D6) δ 0.90 (d, 3H, J )
6.1 Hz, CHCH3), 3.18 (quint., br, 1H, J ) 5.8 Hz, CHCH3),
3.34 (dd, 1H, J ) 10.2, 5.0 Hz, CH)CHSO2), 3.77 (d, 1H, J )
10.6 Hz, CHdCHSO2), 3.96 (d, 1H, J ) 12.3 Hz, OCHHC10H7),
4.25 (d, 1H, J ) 12.3 Hz, OCHHC10H7), 6.83-7.93 (m,
superimposed with major diastereomer, 12H, OCH2C10H7,
meta-, para-, ortho-C-H) ppm; 13C NMR (75 MHz, C6D6) δ
21.85 (CHCH3), 59.30 (CHdCHSO2), 65.32 (CHdCHSO2),
70.07 (OCH2), 74.07 (CHCH3), 126.04-129.09 (OCH2C10H7,
ortho-, para-C, superimposed with major diastereomer and
C6D6), 132.30 (para-C), 133.42-133.62 (OCH2C10H7), 135.31
(ipso-OCH2C10H7), 143.06 (ipso-C), 207.08 (br, superimposed
with major diastereomer, Fe-CO) ppm; IR (KBr) ν 3057, 3014
(w, Ar-C-H), 2991, 2932, 2864 (w, CH, CH2, CH3), 2105 (vs,
axial-Fe-CO), 2049, 2019 (vs), 1988 (vs, br, Fe-CO), 1601,
1583, 1508 (w, Ar-CdC), 1446 (m), 1385 (w, CH3), 1330 (m),
1306 (s, SdO), 1262 (m), 1191 (s), 1140 (s, SdO), 1125 (s), 1084
(s, C-O-C), 1068, 1029 (s-m, br), 935, 902, 864 (m), 810, 751,
717, 689 (s-m), 630, 615 (vs), 587, 579, 563 (s-m) cm-1. MS
(70 eV): m/z (relative intesity) 436 (1.4) [M•+ - 3CO], 408 (18)
[M•+ - 4CO], 352 (1.5) [408 - Fe], 289 (2.4), 267 (100) [408 -
CH2C10H7], 250 (1.6), 211 (6), 196 (6), 186 (10), 167 (6), 157
(2) [OCH2C10H7+], 143 (3) [H2SO2C6H5+], 142 (21), 141 (100)
[C11H9+, SO2C6H5+], 133 (7), 129 (10), 127 (4) [C10H7+], 115 (22),
107 (6) [C7H8O+], 84 (25), 77 (6) [C6H5+], 56 (63) [Fe+], 44 (9).
Anal. Calcd for C25H20FeSO7 (Mr 520.34): C, 57.71; H, 3.87.
Found: C, 57.36; H, 3.98.
352 (5) [M•+ - CO], 324 (14) [M•+ - 2CO], 296 (46) [M•+
-
3CO], 279 (4) [M•+ + 1 - 3CO - H2O], 268 (31) [M•+ - 4CO],
251 (13), 250 (100) [268 - H2O], 186 (27), 184 (48), 169 (29),
160 (23), 149 (16), 143 (3) [H2SO2C6H5+], 133 (19), 125 (17),
78 (9), 77 (19) [C6H5+], 73 (13), 71 (9), 56 (30) [Fe+], 55 (21),
12
53 (8), 51 (15). Calcd for
C
1H1256Fe32S16O4 (M•+ - 3CO)
11
m/z ) 295.98057. Found m/z ) 295.98050.
Tetr a ca r bon yl[(1-2η)-(E,1R,2S,3S)-3-a cetoxy-1-(p h en -
ylsu lfon yl)bu t-1-en ]ir on (0) [(1R,2S,3S)-14f, 14f′, ψ-exo-
14f] a n d Tetr a ca r bon yl[(1-2η)-(E,1S,2R,3S)-3-a cetoxy-1-
(p h en ylsu lfon yl)b u t -1-en ]ir on (0) [(1S,2R,3S)-14f, 14f′′,
ψ-en d o-14f]. By analogy to the procedure for 14a i/a ii, 509 mg
(2.00 mmol) of alkenyl sulfone (S)-6d was reacted with Fe2-
(CO)9 (13) (946 mg, 2.60 mmol) in anhydrous diethyl ether (30
mL) to yield 788 mg (93%) of a yellow-greenish viscous oil after
purification by filtration through a PTFE-filter (contains small
amounts of Fe(CO)5 and Fe3(CO)12).21g,42 Rf: 0.19 (light petro-
leum/diethyl ether ) 2:1). de: 22% (determined by 1H NMR
spectroscopy, 300 MHz, signals: CHCH3, COCH3, CHdCHSO2,
CHCH3). NMR spectroscopic data for the major diastereomer
(1R,2S,3S)-14f (14f′, Ψ-exo-14f): 1H NMR (300 MHz, C6D6) δ
1.11 (d, 3H, J ) 6.3 Hz, CHCH3), 1.20 (s, 3H, COCH3), 3.15
(dd, 1H, J ) 9.9, 9.3 Hz, CHdCHSO2), 4.08 (d, 1H, J ) 10.2
Hz, CHdCHSO2), 4.50 (dq, 1H, J ) 9.1, 6.5 Hz, CHCH3), 6.90-
7.03 (m, superimposed with minor diastereomer, 3H, meta-,
para-C-H), 7.79-7.88 (m, superimposed with minor diaste-
reomer, 2H, ortho-C-H) ppm; 13C NMR (75 MHz, C6D6) δ 20.47
(CHCH3), 21.19 (COCH3, superimposed with minor diastere-
omer), 53.33 (CHdCHSO2), 67.84 (CHdCHSO2), 74.17 (CHCH3),
127.90 (ortho-C), 129.41 (meta-C), 132.52 (para-C), 142.19
(ipso-C), 169.33 (COCH3), 206.37 (br, superimposed with minor
diastereomer, Fe-CO) ppm. NMR spectroscopic data for the
minor diastereomer (1S,2R,3S)-14f (14f′′, Ψ-endo-14f): 1H
NMR (300 MHz, C6D6) δ 0.80 (d, 3H, J ) 6.1 Hz, CHCH3),
1.70 (s, 3H, COCH3), 3.23 (dd, 1H, J ) 10.3, 9.0 Hz, CHd
CHSO2), 3.52 (d, 1H, J ) 10.4 Hz, CHdCHSO2), 4.29 (dq, 1H,
J ) 8.9, 6.2 Hz, CHCH3), 6.90-7.03 (m, superimposed with
major diastereomer, 3H, meta-, para-C-H), 7.79-7.88 (m,
superimposed with major diastereomer, 2H, ortho-C-H) ppm;
13C NMR (75 MHz, C6D6) δ 21.19 (COCH3, superimposed with
major diastereomer), 23.26 (CHCH3), 54.84 (CHdCHSO2),
67.05 (CHdCHSO2), 74.12 (CHCH3), 127.66 (ortho-C), 129.26
(meta-C), 132.78 (para-C), 142.39 (ipso-C), 168.99 (COCH3),
206.37 (br, superimposed with major diastereomer, Fe-CO)
ppm; IR (film on NaCl) ν 3024 (w, Ar-C-H), 2980, 2937 (vw,
CH, CH3), 2107 (vs, trans-Fe-CO), 2032, 2007 (vs, Fe-CO),
1732 (s, CdO), 1585, 1479 (vw, Ar-CdC), 1447 (m), 1372 (m,
CH3), 1308 (s, SdO), 1238 (s, br, CO-O), 1148 (s, SdO), 1085,
Tetr a ca r bon yl[(1-2η)-(E,1R,2S,3S)-1-(p h en ylsu lfon yl)-
bu t-1-en -3-ol]ir on (0) [(1R,2S,3S)-14e, 14e′, ψ-exo-14e] a n d
Tet r a ca r b on yl[(1-2η)-(E,1S,2R,3S)-1-(p h en ylsu lfon yl)-
bu t-1-en -3-ol]ir on (0) [(1S,2R,3S)-14e (14e′′, Ψ-en d o-14e].
By analogy with the procedure for 14a ′/a ′′, 424 mg (2.00 mmol)
of alkenyl sulfone (S)-6e was reacted with Fe2(CO)9 (13) (946
mg, 2.60 mmol) in anhydrous diethyl ether (30 mL) to yield
920 mg (quant.) of a yellow, slightly greenish viscous oil after
purification by filtration through a PTFE-filter (contains small
amounts of Fe(CO)5 and Fe3(CO)12).21g,42 Rf: 0.17 (light petro-
leum/diethyl ether ) 1:1). de: 35% (determined by 1H NMR
spectroscopy, 300 MHz, CHCH3, OH, dCHSO2). NMR spec-
troscopic data for the major diastereomer (1R,2S,3S)-14e (14e′,
Ψ-exo-14e): 1H NMR (300 MHz, C6D6) δ 0.79 (d, 3H, J ) 6.3
Hz, CHCH3), 1.44 (d, 1H, J ) 4.7 Hz, OH), 3.24 (dd, 1H, J )
10.4, 4.1 Hz, CHdCHSO2), 3.37-3.46 (m, 1H, CHCH3), 3.86
(d, 1H, J ) 10.2 Hz, CHdCHSO2), 4.50 (dq, 1H, J ) 9.1, 6.5
Hz, CHCH3), 6.93-7.05 (m, superimposed with minor diaste-
reomer, 3H, meta-, para-C-H), 7.79-7.89 (m, superimposed
with minor diastereomer, 2H, para-C-H) ppm; 13C NMR (75
MHz, C6D6) δ 25.49 (CHCH3), 60.13 (CHdCHSO2), 65.13 (CHd
CHSO2), 69.83 (CHCH3), 127.72-128.36 (ortho-C, superim-
1046 (m), 944 (w), 802, 753, 718, 689 (m), 628, 592 (s) cm-1
;
MS (70 eV) m/z (relative intensity) 366 (4) [M•+ - 2CO], 338
(22) [M•+ - 3CO], 311 (16), 310 (100) [M•+ - 4CO], 279 (2)
[338 - CH3CO2H], 267 (4) [M•+ - 4CO, - H3CCO], 250 (42)

Iron-Mediated Allylic Substitution Reactions
Organometallics, Vol. 20, No. 21, 2001 4331
[310 - H3CCO2H], 230 (4), 220 (4), 203 (4), 186 (44), 184 (31),
was dried for 12 h under reduced pressure at room tempera-
ture in high vacuum, yielding 7.84 g (96%) of a pale yellow
solid. The complex was obtained in spectroscopic and analytical
pure form and was used without further purification in
nucleophilic addition reactions. Screening for syn-Me/anti-Me
selectivity in the formation of complexes 18′/′′ employing
mixtures of complexes 14a ′/a ′′ and 14f′/f′′ was operationally
identically performed. Mp: 153-155 °C (dec). de > 99% (syn-
160 (12), 150 (5), 141 (1.2) [SO2C6H5+], 133 (21), 125 (10), 115
(16), 77 (9) [C6H5+], 56 (30) [Fe+], 53 (12). HRMS: calcd for
12
C
1H1456Fe16O532S (M•+ - 3CO) m/z 337.99113, found m/z
13
337.99087.
Tetr acar bon yl[(1-2η)-(E,1R,2S,3S)-1-m eth oxycar bon yl-
3-(p h en ylm et h oxy)b u t -1-en ]ir on (0) [(1R,2S,3S)-15, 15′,
ψ-en d o-15] a n d Tetr a ca r bon yl[(1-2η)-(E,1S,2R,3S)-1-
m et h oxyca r b on yl-3-(p h en ylm et h oxy)b u t -1-en ]ir on (0)
[(1S,2R,3S)-15, 15′′, Ψ-exo-15]. By analogy with the procedure
for 14a ′/a ′′, 441 mg (2.00 mmol) of ester (S)-8 was reacted with
Fe2(CO)9 (13) (1.46 g, 4.00 mmol) in anhydrous diethyl ether
or n-hexane (15 mL) to yield 660 mg (85%) of a yellow, slightly
greenish viscous oil, which solidifies to needles after purifica-
tion by filtration through a PTFE-filter.21b Additional purifica-
tion by inert gas column chromatography (silica gel, light
petroleum/diethyl ether ) 14:1) gave 477 g (62%) of yellow
light-sensitive crystalline needles. Rf: 0.22 (light petroleum/
diethyl ether ) 14:1). de: 16% (determined by 1H NMR
spectroscopy, 300 MHz, signals: OCH3). CHCH3). NMR spec-
troscopic data of the major diastereomer (1R,2S,3S)-15 (15′,
Me/anti-Me: > 99:1; determined by 1H NMR spectroscopy, 500
21
MHz, signals: CHCH3, CH-CHSO2, CHCH3). ee > 99%. [R]D
:
+158.3 (c 0.96, acetone). NMR spectroscopic data for the
(1R,2S,3R)-18, (18′, syn-Me,syn-SO2Ph-18) isomer: 1H NMR
(500 MHz, CD3NO2) δ 2.13 (d, 3H, J ) 6.4 Hz, CHCH3), 4.64
(dd, 1H, J ) 10.1, 0.6 Hz, CH-CHSO2), 4.93 (dqd, 1H, J )
12.4, 6.4, 0.6 Hz, CHCH3), 6.23 (dd, 1H, J ) 12.4, 10.1 Hz,
CH-CHSO2), 7.72-7.80 (m, 2H, meta-C-H), 7.82-7.91 (m,
1H, para-C-H), 8.07-8.14 (m, 2H, ortho-C-H) ppm; 13C NMR
(125 MHz, CD3NO2) δ 20.77 (CHCH3), 73.73 (CH-CHSO2),
90.58 (CHCH3), 97.65 (CH-CHSO2), 129.46 (ortho-C), 131.54
(meta-C), 136.61 (para-C), 139.57 (ipso-C), 195.35, 196.10,
197.43, 197.67 (Fe-CO) ppm. All additional spectroscopic and
analytical data correspond with those reported in the liter-
ature.21g,42
1
Ψ-endo-15): H NMR (300 MHz, C6D6) δ 1.09 (d, 3H, J ) 6.1
Hz, CHCH3), 3.23 (br. qd, J ) 6.1, 5.2 Hz, CHCH3), 3.40 (s,
3H, OCH3), 3.85 (dd, 1H, J ) 11.0, 5.2 Hz, CHdCHCO2), 3.98
(d, 1H, J ) 11.6 Hz, OCHHC6H5), 4.20 (br d, 1H, J ) 11.9 Hz,
CHdCHCO2), 4.24 (d, 1H, J ) 11.6 Hz, OCHHC6H5), 7.04-
7.23 (m, superimposed with minor diastereomer, 5H, OCH2-
C6H5) ppm; 13C NMR (75 MHz, C6D6) δ 22.77 (CHCH3), 42.95
(CHdCHCO2), 51.25 (OCH3), 66.29 (CHdCHCO2), 70.55
(OCH2C6H5), 75.60 (CHCH3) 127.68-128.50 (OCH2C6H5, su-
perimposed with minor diastereomer and C6D6), 138.37 (ipso-
OCH2C6H5), 174.93 (CHdCHCO2), 208.51 (br, Fe-CO) ppm.
NMR spectroscopic data of the minor diastereomer (1S,2R,3S)-
15 (15′′, Ψ-exo-15): 1H NMR (300 MHz, C6D6) δ 1.23 (d, 3H, J
) 6.1 Hz, CHCH3), 3.33 (d, 1H, J ) 11.3 Hz, OCHHC6H5), 3.34
(br quint., J ) 6.0 Hz, CHCH3), 3.37 (s, 3H, OCH3), 3.80 (dd,
1H, J ) 10.9, 6.0 Hz, CHdCHCO2), 4.12 (br d, 1H, J ) 11.9
Hz, CHdCHCO2), 4.28 (d, 1H, J ) 11.6 Hz, OCHHC6H5), 7.04-
7.23 (m, superimposed with major diastereomer, 5H, OCH2C6H5)
ppm; 13C NMR (75 MHz, C6D6) δ 22.24 (CHCH3), 44.78 (CHd
CHCO2), 51.35 (OCH3), 63.92 (CHdCHCO2), 70.19 (OCH2C6H5),
77.78 (CHCH3), 127.68-128.50 (OCH2C6H5, superimposed
with major diastereomer and C6D6), 138.48 (ipso-OCH2C6H5),
174.65 (CHdCHCO), 208.37 (br, Fe-CO) ppm; IR (CHCl3) ν
3026, 3012 (w, Ar-C-H), 2952, 2868 (w, CH, CH3), 2098 (vs,
axial-Fe-CO), 2023, 1993 (vs, Fe-CO), 1701 (s, CdO), 1604,
1500, 1477 (w, Ar-CdC), 1455, 1435 (m), 1373 (w, CH3), 1348
(w), 1265, 1193 (m), 1173 (s, C-O-C), 1062, 1027 (w), 908
(w), 699, 669 (m), 629 (vs) cm-1; MS (70 eV) m/z (relative
intensity) 388 (0.5) [M•+], 357 (1.0) [M•+ - OCH3], 332 (2) [M•+
- 2CO], 304 (5) [M•+ - 3CO], 277 (13), 276 (55) [M•+ - 4CO],
218 (7), 193 (4), 185 (45) [276 - CH2C6H5], 168 (26), 163 (8),
133 (5), 114 (12), 92 (16), 91 (100) [C7H7+], 82 (11), 79 (9), 77
(9) [C6H5+], 65 (12) [C5H5+], 56 (26) [Fe+], 53 (12), 39 (12).
r a c-Tetr a ca r bon yl[(1-3η)-1-(p h en ylsu lfon yl)bu t-1-en -
3-yl]ir on (1+) Tetr a flu or obor a te r a c-18′ (r a c-syn -Me,syn -
SO2P h -18) a n d r a c-18′′ (r a c-a n ti-Me,syn -SO2P h -18). Rep-
resentative procedure: By analogy with the conversion of (S)-
6f to complexes 14f ′/f ′′, 12.7 g (50 mmol) of the racemic
alkenyl sulfone rac-6f was reacted with Fe2(CO)9 (23.7 g, 75
mmol) (13) in anhydrous diethyl ether (300 mL).21g,42 After
completion of the reaction, filtration over Celite/sand, and
several washings with anhydrous diethyl ether, the combined
filtrate was partially evaporated under reduced pressure to
yield a bright yellow clear solution of complex mixture rac-
14f′/f′′. By analogy with the procedure for the synthesis of
complex 18′, the solution was carefully warmed to 30 °C, and
8.9 mL (65 mmol) of a 54% solution of HBF4 in diethyl ether
was added dropwise. After 2 h, the precipitate was filtered off
under an atmosphere of argon and washed with anhydrous
diethyl ether until the filtrate was colorless. Drying in high
vacuum yielded 21.2 g (94%) of a pale yellow solid. The complex
mixture was obtained in spectroscopic and analytical pure form
and was used without further purification in nucleophilic
addition reactions. Mp: 153-155 °C (dec). de: 49% (syn-Me/
anti-Me: 2.94:1; determined by 1H NMR spectroscopy, 500
MHz, signals: CHCH3, CH-CHSO2, CHCH3). NMR spectro-
scopic data for the minor diastereomer rac-18′′ (rac-anti-
Me,syn-SO2Ph-18): 1H NMR (500 MHz, CD3NO2) δ 1.77 (d,
3H, J ) 7.3 Hz, CHCH3), 5.30 (d, 1H, J ) 11.0 Hz, CH-
CHSO2), 5.85 (dq, br., 1H, J ) 9.1, 7.2 Hz, CHCH3), 6.12 (dd,
br, 1H, J ) 11.0, 9.0 Hz, CH-CHSO2), 7.72-7.80 (m, 2H, meta-
C-H, superimposed with major diastereomer), 7.82-7.91 (m,
1H, para-C-H, superimposed with major diastereomer), 8.07-
8.14 (m, 2H, ortho-C-H, superimposed with major diastere-
omer) ppm; 13C NMR (125 MHz, CD3NO2) δ 20.15 (CHCH3),
77.73 (CH-CHSO2), 92.56 (CHCH3), 94.46 (CH-CHSO2),
129.63 (ortho-C), 131.54 (meta-C, superimposed with major
diastereomer), 136.61 (para-C, superimposed with major di-
astereomer), 139.33 (ipso-C), 195.05, 196.30, 197.44, 197.79
(Fe-CO) ppm. All additional spectroscopic and analytical data
correspond with those of the major diastereomer rac-18′ (rac-
syn-Me,syn-SO2Ph-18).21g,42
12
HRMS: calcd for C141H1656Fe16O4 (M•+ - 3CO) m/z 304.03980,
found m/z 304.04008.
Tet r a ca r b on yl[(1-3η)-(1R,2S,3R)-1-(p h en ylsu lfon yl)-
bu t-1-en -3-yl]ir on (1+) Tetr a flu or obor a te [(1R,2S,3R)-18,
18′, syn -Me,syn -SO2P h -18]. Representative procedure: 8.54
g (18.2 mmol) of complex (1R,2S,3S)-14a (14a ′, Ψ-exo-14a ; de
) ee > 99%) was dissolved in 50 mL of anhydrous diethyl ether
under an atmosphere of argon.21g,42 The bright yellow solution
was taken up into a syringe and filtered through a PTFE-
syringe filter into a 500 mL Schlenk flask. The solution was
diluted up to a total volume of 250-300 mL with anhydrous
diethyl ether and then warmed carefully to 30 °C. A 3.0 mL
(21.8 mmol) sample of a 54% solution of HBF4 in diethyl ether
was added dropwise to the solution. After 2 h, the precipitate
was filtered off under an atmosphere of argon using an inert
gas frit. The collected precipitate was washed with anhydrous
diethyl ether until the filtrate remained colorless. The residue
Tet r a ca r b on yl[(1-3η)-(1R,2S,3R)-1-(m et h oxyca r b on -
yl)bu t-1-en -3-yl]ir on (1+) Tetr a flu or obor a te [(1R,2S,3R)-
19, 19′, a n ti-Me,syn -CO2Me-19] a n d Tetr a ca r bon yl[(1-
3η)-(1S,2R,3R)-1-(m et h oxyca r b on yl)b u t -1-en -3-yl]ir on -
(1+) Tetr a flu or obor a te [(1S,2R,3R)-19, 19′′, syn -Me,syn -
CO2Me-19]. By analogy with the procedure for the synthesis
of rac-14f′/f′′ and rac-18′/′′, 440 mg (2.0 mmol) of the ester (S)-8
was reacted with 1.46 g (4.0 mmol) of Fe2(CO)9 (13) in
anhydrous diethyl ether (15 mL). The reaction mixture was

4332 Organometallics, Vol. 20, No. 21, 2001
Enders et al.
filtered twice, diluted with anhydrous diethyl ether to give a
total volume of 20 mL, and warmed to 30 °C. A 0.33 mL (2.4
mmol) portion of a 54% solution of HBF4 in diethyl ether was
added dropwise. After 2 h, the precipitate was filtered off under
an atmosphere of argon, washed with anhydrous diethyl ether,
and dried in high vacuum to yield 640 mg (87%) of a pale
yellow solid. The complex was obtained in spectroscopic and
analytical pure form and was used without further purification
in nucleophilic addition reactions. Mp: 89-90 °C (dec). de )
9% (syn-Me/anti-Me ) 1.0:1.19; determined by 1H NMR
spectroscopy, 500 MHz, signals: CHCH3, CH-CHCO2CH3).
NMR spectroscopic data for the major (1R,2S,3R)-19 (19′, anti-
Me,syn-CO2Me-19): 1H NMR (500 MHz, CD3NO2) δ 1.85 (dd,
3H, J ) 7.3, 0.9 Hz, CHCH3), 3.93 (s, 3H, OCH3), 4.27 (dd,
1H, J ) 11.9, 0.9 Hz, CH-CHCO2), 5.88 (dqd, 1H, J ) 8.2,
7.0, 0.9 Hz, CHCH3), 6.24 (ddd, 1H, J ) 11.6, 8.2, 0.9 Hz, CH-
CHCO2) ppm; 13C NMR (125 MHz, CD3NO2) δ 19.91 (CHCH3),
54.59 (CO2CH3), 57.85 (CH-CHCO2), 90.60 (CHCH3), 97.53
(CH-CHCO2), 171.08 (CO2CH3), 195.93, 197.17, 198.46, 198.60
(Fe-CO) ppm. NMR spectroscopic data for the minor diaste-
reomer (1S,2R,3R)-19 (19′′, syn-Me,syn-CO2Me-19): 1H NMR
(500 MHz, CD3NO2) δ 2.19 (d, br, 3H, J ) 6.4 Hz, CHCH3),
3.64 (d, 1H, J ) 10.7 Hz, CH-CHCO2), 3.90 (s, 3H, OCH3),
4.97 (dqd, 1H, J ) 12.5, 6.4, 0.9 Hz, CHCH3), 6.35 (ddd, 1H, J
) 12.5 Hz, 10.7 Hz, 0.9 Hz, CH-CHCO2) ppm; 13C NMR (125
MHz, CD3NO2) δ 21.11 (CHCH3), 53.38 (CH-CHCO2), 54.53
(CO2CH3), 89.26 (CHCH3), 100.83 (CH-CHCO2), 171.44 (CO2-
CH3), 196.27, 196.92, 198.15, 198.73 (Fe-CO) ppm. All ad-
ditional spectroscopic and analytical data correspond to those
reported in the literature.21b
Ack n ow led gm en t. This work was supported by the
Volkswagen-Stiftung, the Fonds der Chemischen In-
dustrie, the Deutsche Forschungsgemeinschaft (Leibniz
award), and the European Union (Human Capital and
Mobility Network: Metal Mediated and Catalyzed
Organic Synthesis, MMCOS). We thank the companies
BASF AG, Bayer AG, the former Boehringer Mannheim
AG, Degussa AG, and the former Hoechst AG for their
kind donation of chemicals. Dr. Tetsuo Uno (Genomics
Institute of the Novartis Research Foundation, San
Diego) is acknowledged for checking the manuscript.
Su p p or tin g In for m a tion Ava ila ble: Synthetic proce-
dures and full analytical data for compounds (S)-2, (S)-3a -d ,
(S)-4a -d , (S)-6a -f, (S)-8, (R)-23, and (S)-24. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010343L