Preparation, characterization, and reactivity of (3-methylpentadienyl) iron(1+) cations

Article abstract of DOI:10.1021/om7006248

The title cations (9 and 12) were prepared by dehydration of (3-methyl-2,4-pentadien-l-ol)Fe(CO)₂L⁺ complexes. The structure of the (CO)₂PPh₃-ligated 12 was determined by single-crystal X-ray analysis. Reaction of carbon and heteroatom nucleophiles to (3-methylpentadienyl)Fe(CO)₃⁺ cations 9 and 12 proceeds either via attack at the dienyl terminus to give (3-methyl-l,3Z-diene)iron complexes or via attack at the internal carbon, followed by carbon monoxide insertion and reductive elimination to afford 3-methyl-4-substituted cyclohexenones. Cyclohexenone formation was found to be prevalent for addition of stabilized nucleophiles with strongly dissociated counterions to cation 9 (L = CO). Reaction of cation 9 with sodium bis[(-)-8-phenylmenthyl] malonate gave a single diastereomeric cyclohexenone.

Full text of DOI:10.1021/om7006248

Organometallics 2007, 26, 5295-5303
5295
Preparation, Characterization, and Reactivity of
(3-Methylpentadienyl)iron(1+) Cations
Subhabrata Chaudhury,† Shukun Li,† Dennis W. Bennett,‡ Tasneem Siddiquee,‡
Daniel T. Haworth,† and William A. Donaldson*,†
Department of Chemistry, Marquette UniVersity, P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, and
Department of Chemistry and Biochemistry, UniVersity of WisconsinsMilwaukee,
Milwaukee, Wisconsin 53201-0413
ReceiVed June 22, 2007
The title cations (9 and 12) were prepared by dehydration of (3-methyl-2,4-pentadien-1-ol)Fe(CO)2L+
complexes. The structure of the (CO)2PPh3-ligated 12 was determined by single-crystal X-ray analysis.
+
Reaction of carbon and heteroatom nucleophiles to (3-methylpentadienyl)Fe(CO)3 cations 9 and 12
proceeds either via attack at the dienyl terminus to give (3-methyl-1,3Z-diene)iron complexes or via
attack at the internal carbon, followed by carbon monoxide insertion and reductive elimination to afford
3-methyl-4-substituted cyclohexenones. Cyclohexenone formation was found to be prevalent for addition
of stabilized nucleophiles with strongly dissociated counterions to cation 9 (L ) CO). Reaction of cation
9 with sodium bis[(-)-8-phenylmenthyl] malonate gave a single diastereomeric cyclohexenone.
Chart 1
Introduction
There are a variety of monoterpenes (e.g., cis-ocimenol, 1),1
sesquiterpenes (e.g., luzonensin, 2),2 and diterpenes which
possess a 3-methyl-1,3(Z)-pentadienyl segment (Chart 1).
Certain of these compounds exhibit useful biological activity.
For example, the furanoic acid 33 inhibits bee venom phospho-
lipase A2 in vitro (IC50 ) 0.5 µM) while cis-communic acid4
(4) exhibits antibacterial activity against Gram positive bacteria.
Alternatively, the clerodane caseargrewiin D5 (5) demonstrates
both antimalarial and antitumor activity and casearinone B6 (6)
has potential as an immunosuppressive agent since it inhibits
binding of leukocyte function antigen-1 (LFA-1) to intercellular
adhesion molecule-1 (ICAM-1). To our knowledge, there are
no reported syntheses of any 3-methyl-1,3(Z)-pentadienyl-
containing diterpenes.7
One potential route for the introduction of a 3-methyl-1,3-
(Z)-pentadienyl functionality involves the addition of nucleo-
philes to a (3-methylpentadienyl)Fe(CO)2L+ cation, followed
by decomplexation of the metal (Scheme 1). We here report on
Scheme 1
* To whom correspondence should be addressed. E-mail:
william.donaldson@marquette.edu.
† Marquette University.
‡ University of WisconsinsMilwaukee.
(1) Williams, P. J.; Strauss, C. R.; Wilson, B.; Massy-Westropp, R. A.
J. Agric. Food Chem. 1982, 30, 1219-1223.
the preparation, structural characterization, and reactivity of (3-
methylpentadienyl)iron(1+) cations.
(2) Kuniyoshi, M.; Marma, M. S.; Higa, T.; Bernardinelli, G.; Jefford,
C. W. J. Nat. Prod. 2001, 64, 696-700.
(3) (a) Coll, J. C.; Mitchell, S. J.; Stokie, G. J. Tetrahedron Lett. 1977,
1539-1542. (b) Grace, K. J. S.; Zavortink, D.; Jacobs, R. S. Biochem.
Pharmacol. 1994, 47, 1427-1434.
Results and Discussion
Preparation and Characterization of (3-Methylpentadi-
enyl)iron(1+) Cations. The (dienoate)iron complex 7 was
prepared in two steps from ethyl 3-methyl-4-oxo-2-butenoate
according to the literature procedure.8 Reduction of 7 gave the
known8 (dienol)iron complex 8, which upon dehydration with
HPF6/Ac2O gave 9 as a stable pale yellow solid (Scheme 2).
(4) Bohlmann, F.; Zdero, C. Chem. Ber. 1974, 107, 1416-1419.
Muhammad, I.; Mossa, J. S.; Al-Yahya, M. A.; Ramadan, A. F.; El-Feraly,
F. S. Photother. Res. 1995, 9, 584-588.
(5) Kanokmedhakul, S.; Kanokmedhakul, K.; Kanarsa, T.; Buayairaksa,
M. J. Nat. Prod. 2005, 68, 183-188.
(6) Hunter, M. S.; Corley, D. G.; Carron, C. P.; Rowold, E.; Kilpatrick,
B. F.; Durley, R. C. J. Nat. Prod. 1997, 60, 894-899.
(7) There are only two syntheses reported of crotomachlin, a 3-methyl-
1,3(E)-pentadienyl-containing labdane diterpene: (a) Harlem, D.; Khuong-
Huu, F.; Kende, A. S. Tetrahedron Lett. 1993, 34, 5587. (b) Teramoto, T.;
Yono, T.; Morita, H.; Katsumura, S.; Sakaguchi, K.; Isoe, S. Synlett 1996,
141.
(8) Adams, C. M.; Cerioni, G.; Hafner, A.; Kalchhauser, H.; von
Philipsborn, W.; Prewo, R.; Schwenk, A. HelV. Chim. Acta 1988, 71, 1116-
1142.
10.1021/om7006248 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 09/26/2007

5296 Organometallics, Vol. 26, No. 22, 2007
Chaudhury et al.
Scheme 2
Scheme 3
Figure 1. ORTEP of the cationic portion of 12 (50% elipsoids).
Selected bond lengths (Å): Fe(1)-C(3), 2.180(11); Fe(1)-C(4),
2.120(11); Fe(1)-C(5), 2.188(11); Fe(1)-C(6), 2.116(8); Fe(1)-
C(7), 2.132(9); C(3)-C(4), 1.336(17); C(4)-C(5), 1.422(15);
C(5)-C(6), 1.440(14); C(6)-C(7), 1.390(14).
Chart 2
Cation 9 was assigned the symmetrical cisoid structure shown;
1
the H and 13C NMR spectra of 9 consisted of four and five
signals, respectively. It is well-known that replacement of CO
by a phosphine ligand can affect the regioselectivity of
nucleophilic addition to dienyl iron complexes.9 Ligand sub-
stitution of 7 with triphenylphosphine in the presence of
trimethylamine N-oxide gave 10. Reduction of 10 gave 11,
which upon dehydration with HPF6/Ac2O gave 12 as a stable
golden yellow solid.
at low temperature due to the apical phosphine rotomer. The
internal dienyl hydrogens H2 and H2′ coalesce at -10 °C,
corresponding to kc) 349 s-1 and ∆Gq )12.8 kcal mol-1. This
activation energy is comparable with that found for apical-
basal phosphite exchange in (cyclohexadienyl)Fe(CO)2(EPTB)+
(13) and (cycloheptadienyl)Fe(CO)2(EPTB)+ (14) (9.8 and 11.4
kcal mol-1, respectively)10 and basal-basal phosphine exchange
1
The H NMR spectrum of 12 at 16 °C consisted of a set of
four broad signals (3:2:2:2) for the pentadienyl ligand portion.
The signal for the methyl protons was observed at δ 2.37 ppm
(3H) as well as three broad multiplets at δ 5.71, 2.95, and 1.94
ppm (2H each). Upon lowering of the temperature, the multiplets
decoalesce and eventually at -70 °C separate into four
multiplets integrating to 1H each and one multiplet integrating
to 2H. This fluxional behavior is characteristic of a tetragonal
pyramidal iron complex in which the phosphine ligand is rapidly
exchanging between basal sites (12B and 12B′; Scheme 3). At
16 °C, the “windshield-wiper” motion of the Ph3P(CO)2Fe
moiety is sufficiently fast that only time-averaged signals appear
for the pairs Ha/Ha′, Hb/Hb′, and H2/H2′. As the temperature is
lowered, rotation about the Fe-dienyl ligand slows, and the
phosphine occupies one of two equivalent basal sites. With the
loss of the symmetry, protons Ha, Hb, and H2 become non-
equivalent with Ha′, Hb′, and H2′, respectively. No additional
resonances were observed in the 1H NMR spectrum that
might correspond to an apical isomer conformation (12A). This
was further corroborated by a variable-temperature 31P NMR
study. In this case, only a single resonance (δ 62.4 ppm) was
observed for the phosphine ligand in the temperature range 16
to -70 °C. Exchange of the phosphine ligand between
equivalent basal sites gives rise to a single 31P NMR resonance
signal; if basal-apical exchange of the phosphine ligand had
occurred, an additional 31P NMR resonance would be expected
+
in (bicyclo[5.1.0]octadienyl)Fe(CO)2PPh3 (15) (13.3 kcal
mol-1).11
The crystal structure of 12 (Figure 1) represents the first X-ray
crystal structure of an acyclic dicarbonyl triphenylphosphine
ligated (pentadienyl)iron cation and may be compared with the
structures for 16 and 17 (Chart 2).12 The structure for 12 revealed
that the triphenylphosphine ligand occupies the basal site in the
solid state. For 12 the distances between iron and the pentadienyl
termini (i.e., Fe-C3 and Fe-C7) are not equal; the distance
for the Fe-pentadienyl terminus trans to the PPh3 ligand (i.e.,
Fe-C3) is 0.048 Å greater than for the Fe-pentadienyl terminus
cis to the PPh3 ligand (i.e., Fe-C7). For cation 17, the distance
(10) Whitesides, T. H.; Budnik, R. A. Inorg. Chem. 1975, 14, 664-
676.
(11) Wallock, N. J.; Donaldson, W. A. J. Org. Chem. 2004, 9, 2997-
3007.
(12) (a) Rheingold, A. L.; Haggerty, B. S.; Ma, H.; Ernst, R. D. Acta
Cryst. 1996, C52, 1110-1112. (b) Hudson, R. D. A.; Anson, C. E.; Mahon,
M. F.; Stephenson, G. R. J. Organomet. Chem. 2001, 630, 88-103.
(9) (a) Pearson, A. J.; Kole, S. L.; Ray, T. J. Am. Chem. Soc. 1984, 106,
6060-6074. (b) McDaniel, K. F.; Kracker, L. R.; Thamburaj, P. K.
Tetrahedron Lett. 1990, 31, 2373-2376. (c) Millot, N.; Guillou, C.; Thal,
C. Tetrahedron Lett. 1998, 39, 2325-2326. (d) Barmann, H.; Prahlad, V.;
Tao, C.; Yun, Y. K.; Wang, Z.; Donaldson, W. A. Tetrahedron 2000, 56,
2283-2295.

(3-Methylpentadienyl)iron(1+) Cations
Organometallics, Vol. 26, No. 22, 2007 5297
Scheme 4
between the Fe-pentadienyl terminius trans to the PPh3 ligand
(Fe-C25, numbering taken from ref 12b) is also greater (by
0.127 Å) than for the Fe-pentadienyl terminus cis to the PPh3
ligand (Fe-C21). While this greater Fe-C distance may be
largely attributed to steric hindrance for 17,12b for the 3-meth-
ylpentadienyl ligand (12) this greater distance is presumably
due to the greater trans influence13 of a phosphine compared to
CO; the PPh3 ligand weakens the Fe-C bond trans to itself. In
a comparison of bond angles within the pentadienyl ligand, for
cation 12 the central bond angle (C4-C5-C6 ) 120.3°) is
smaller than the adjacent bond angles about C4 and C6 (C3-
C4-C5 ) 128.7°, C5-C6-C7 ) 125.1°). This is opposite for
16 where the central pentadienyl C-C-C bond angle (C5-
C6-C7 ) 129.1, numbering taken from ref 12a) is larger than
the adjacent angles (C4-C5-C6 ) 121.2°, C6-C7-C8 )
122.0°).12 These differences in bond angle are presumably due
to the differences in substitution at these carbons. The smaller
bond angles are observed at the methyl-substituted pentadienyl
carbons. The steric size of the methyl group is likely to increase
the outside C-C-C bond angles (i.e., C4-C5-C8 in 12) at
the expense of the inner bond angle.
Reactivity of (3-Methylpentadienyl)iron(1+) Cations.14
The reaction of 9 with hydride, methyl cuprate, and triph-
enylphosphine gave (3-methyl-1,3Z-pentadiene)Fe(CO)3 com-
plexes 18a-c, while reaction with excess furan gave (3-methyl-
1,3E-pentadiene)Fe(CO)3 complexes 19d (Scheme 4). Reaction
of 9 with methanol gave an inseparable mixture E- and Z-diene
complexes (19e/18e, 5:2). Structural assignments for these
products were made on the basis of their NMR spectral data.
In particular, the signals for H1endo and H4exo of 1,3Z-diene
complexes 18 appear at ca. δ 0.9-1.3 and 2.4-2.9 ppm,
respectively, while signals for H1endo and H4endo of 1,3E-diene
complexes 19 appear at ca. δ 0.2-0.3 and 1.1-1.9 ppm.
Furthermore, the 3-methyl-1,3Z-pentadiene complex 18a was
identified by comparison of its 13C NMR spectral data with the
literature values,15 while the structural assignment for phos-
phonium salt 18c was corroborated by the X-ray crystal structure
Figure 2. ORTEP of phosphonium salt 18c (50% elipsoids).
Selected bond lengths (Å): Fe(1)-C(1), 2.090(7); Fe(1)-C(2),
2.061(7); Fe(1)-C(3), 2.056(7); Fe(1)-C(4), 2.106(6); P(1)-C(5),
1.810(6); C(1)-C(2), 1.398(12); C(2)-C(3), 1.417(11); C(3)-C(4),
1.435(9); C(4)-C(5), 1.535(8).
(Figure 2). The bond lengths and angles for 18c are consistent
with those of other dienylphosphonium salts.16
Reaction with lithium dimethyl malonate gave the 1,3Z-diene
complex 18f in good yield (Table 1, entry 1). It was thus
surprising that changing the malonate counterion to sodium
followed by treatment of the reaction mixture with methanolic
NaHCO3, gave the 4,5-disubstituted cyclohexenone 20f (entry
2). This difference in reactivity was attributed to the association
of the malonate nucleophile with the counterion: the reaction
of 9 with lithium dimethyl malonate in the presence of
12-crown-4 gave only the cyclohexenone product 20f, while
reaction of 9 with sodium dimethyl malonate/ZnCl2 gave only
the diene complex 18f. This difference in product formation
was also dependent on the steric bulk of the carbon nucleophile.
Reaction with lithium dimethyl methylmalonate anion afforded
the diene complex 18g (entry 5) and reaction with the sodium
salt of this nucleophile gave a separable mixture of 18g and
cyclohexenone 20g (entry 6), while reaction with the sodium
salt of 2-(ethoxycarbonyl)cyclohexanone gave the diene complex
18h (as a mixture of diastereomers, entry 7). In contrast, reaction
of 9 with lithium methyl cyclohexanecarboxylate gave a mixture
of 2- and 3-cyclohexenones 20i. Finally, reaction with potassium
phthalimide gave a mixture of diene complex 18j, 2- and
3-cyclohexenones 20j (entry 9).
The diene complexes 18f,g,h,j were identified by comparison
of their NMR spectral data with that for other 3-methyl-1,3Z-
diene complexes (vide supra). The 2-cyclohexenone products
20f,g,i,j were also identified on the basis of their NMR
spectroscopic data. In particular, signals for H2 and H3 appear
(13) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.
1973, 10, 335-422.
(14) Preliminary communication: Chaudhury, S.; Donaldson, W. A. J.
Am. Chem. Soc. 2006, 128, 5984-5985.
(16) (a) Guy, J. J.; Reichert, B. E.; Sheldrick, G. M. Acta Crystallogr.,
Sect. B 1976, B32, 2504-2506. (b) Donaldson, W. A.; Shang, L.; Rogers,
R. D. Organometallics 1994, 13, 6-7. (c) Donaldson, W. A.; Shang, L.;
Ramaswamy, M.; Droste, C. A.; Tao, C.; Bennett, D. W. Organometallics
1995, 14, 5119-5126.
(15) Adams, C. M.; Cerioni, G.; Hafner, A.; Kalchhauser, H.; von
Philipsborn, W.; Prewo, R.; Schwenk, A. HelV. Chim. Acta 1988, 71, 1116-
1142.

5298 Organometallics, Vol. 26, No. 22, 2007
Chaudhury et al.
Table 1. Addition of Stabilized Carbon and Nitrogen
Scheme 5
+
Nucleophiles to (3-Methylpentadienyl)Fe(CO)3
(Table 1). For strongly associated counterions (e.g., Li+ or Zn2+
,
entries 1, 4, 5) attack on a terminal carbon of the cisoid form
of the cation gives 18. In contrast, for more weakly associated
counterions (e.g., Na+ or Li+/12-crown-4, entries 2, 3, 6)
nucleophilic attack proceeds predominantly at the C2 internal
carbon to generate a (pentenediyl)iron complex 22 (Scheme 5).
Carbonyl insertion20 into 22 affords the acyl complex 23 which
upon reductive elimination gives the 3-cyclohexenone 24.21
Workup with methanolic NaHCO3 effects conjugation to give
the product 20. On the basis of 13C NMR spectroscopy22 and
DFT calculations23c the C2/C4 carbons of the pentadienyl ligand
are believed to bear greater partial positive charge than the C1/
C3/C5 positions, while molecular orbital calculations indicate
that the LUMO of the (dienyl)iron cations has greater orbital
contribution from C1/C5 than from C2/C4.22a,24 Thus, for
strongly dissociated malonate nucleophiles attack at C2/C4 is
believed to be due to charge control, while for nucleophiles
where there is greater association between the malonate anion
and the counterion the decreased polarization in electron density
would lead to frontier orbital controlled nucleophilic attack at
C1/C5. It should be noted that the steric bulk and/or the strength
of the nucleophile may play additional roles in directing
nucleophilic attack. For the bulky 2-(ethoxycarbonyl)cyclohex-
anone nucleophile (Na+ counterion), attack occurs at the less
hindered pentadienyl terminus, while for methyl cyclohexan-
ecarboxylate nucleophile (Li+ counterion) attack occurs at C2.
a After 2 h, the reaction mixture was diluted with CH2CI2 and methanolic
NaHCO3 was 1added. The mixture was stirred for an additional 18 h. b The
product is a mixture of diastereomers at the new chiral center (/) and the
(diene)Fe coordination. c The product is a 6:1 mixture of 2- and 3-cyclo-
hexenones. d 23 ˚C. e The product is a 2.5:1 mixture of 2- and 3-cyclohex-
enones.
at ca. δ 5.8-5.9 (d, J ) 10.1 Hz) and 6.1-6.2 (dd, J ) 10.1,
6.1 Hz) ppm, respectively; the 6.1 Hz coupling (H3-H4) is
consistent with a pseudoequatorial disposition for H4.
In solution, acyclic (pentadienyl)iron cations are known to
exist in an equilibrium between the cisoid form (i.e., 9) and the
corresponding less stable transoid form (i.e., 21, Scheme 5).17
While NMR spectroscopy reveals that 9 exists predominantly
in the cisoid form (vide supra), reactions of (pentadienyl)Fe-
+
(CO)3 cations with weak nucleophiles, such as methanol (N
) 7.73)18a or furan (N ) 1.36),18b proceed via the less stable
but more reactive transoid form.19 Thus, the reaction of 9 with
furan or methanol gives predominantly the 3-methyl-1,3E-
pentadiene products 19d,e. In contrast, stronger nucleophiles
such as hydride, methyl cuprate, and triphenylphosphine (N ≈
13)18a attack on a terminal carbon of the cisoid form of the cation
to give the 3-methyl-1,3Z-pentadiene products 18a-c. For
malonate anions, diene complexes 18f/g or cyclohexenones 20f/g
are formed depending on the counterion of the nucleophile
(20) Carbonyl insertion into (pentenediyl)iron complexes and reductive
elimination have previously been reported: (a) Aumann, R. J. Am. Chem.
Soc. 1974, 96, 2631-2632. (b) Schulze, M. M.; Gockel, U. J. Organomet.
Chem. 1996, 525, 155-158. (c) Taber, D. F.; Kanai, K.; Jiang, Q.; Bui, G.
J. Am. Chem. Soc. 2000, 122, 6807-6808.
(21) A similar mechanism has been proposed to account for the formation
of cyclohexenones from nucleophilic attack of organolithiums on (penta-
dienyl)iron(1+) cations: McDaniel, K. F.; Kracker, L. R., II; Thamburaj,
P. K. Tetrahedron Lett. 1990, 31, 2373-2376.
(22) (a) Dobosh, P. A.; Gresham, D. G.; Lillya, C. P.; Magyar, E. S.
Inorg. Chem. 1978, 17, 1775-1781. (b) Birch, A. J.; Westerman, P. W.;
Pearson, A. J. Aust. J. Chem. 1976, 29, 1671-1677.
(17) Sorensen, T. S.; Jablonski, C. R. J. Organomet. Chem. 1970, 25,
C62-C66.
(18) Nucleophilicity parameters (N, s) for neutral nucleophiles have been
assigned from correlation analysis: (a) Mayr, H.; Patz, M. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 938-957. (b) Mayr, H.; Bug, T.; Gotta, M. F.;
Hering, N.; Irrgang, B.; Janker, B.; Kempf, B.; Loos, R.; Ofial, A. R.;
Remennikov, G.; Schimmel, H. J. Am. Chem. Soc. 2001, 123, 9500-9512.
(19) Hossain, M. A.; Jin, M.-J.; Donaldson, W. A. J. Organomet. Chem.
2001, 630, 5-10 and references therein.
(23) (a) Clack, D. W.; Monshi, M.; Kane-Maguire, L. A. P. J. Organomet.
Chem. 1976, 107, C40-C42. (b) Hoffmann, R.; Hofmann, P. J. J. Am.
Chem. Soc. 1976, 98, 598-604. (c) Pfletschinger, A.; Schmalz, H.-G.; Koch,
W. Eur. J. Inorg. Chem. 1999, 1869-1880.
(24) (a) Eisenstein, O.; Butler, W. M.; Pearson, A. J. Organometallics
1984, 3, 1150-1157. (b) Pearson, A. J.; Burello, M. P. Organometallics
1992, 11, 448-456.

(3-Methylpentadienyl)iron(1+) Cations
Organometallics, Vol. 26, No. 22, 2007 5299
Scheme 6
Figure 3. Diastereomeric transition states for addition to (3-
methylpentadienyl)Fe(CO)3+. The Fe(CO)3 fragment, which is away
from the direction of the viewer, is not shown for clarity.
Scheme 7
This regioselectivity may be due to the greater strength of this
ester enolate compared to malonate (i.e., charge control).
Reaction of the Fe(CO)2PPh3 ligated cation 12 with a variety
of nucleophiles gave only the 1,3Z-diene complexes 25 in good
to excellent yields; no reaction was observed with the weak
nucleophiles furan or methanol (Scheme 6). Products 25 were
assigned as (3-methyl-1,3Z-pentadiene)Fe(CO)2PPh3 complexes
on the basis of their NMR spectral data. In particular, the
resonance for H2 appears as a broad signal at ca. δ 4.0-4.4
ppm, while the resonances for C2 appear at ca. δ 93-95 ppm.
Notably, the signal for C2 of (3-methyl-1,3E-pentadiene)Fe-
(CO)2PPh3 complexes (cf. 10 and 11) appears further upfield
(ca. δ 86-88 ppm). Complex 25h was formed as an inseparable
mixture of diastereomers at the new chiral center and the (diene)-
N-propionyloxazolidinones25c resulted in enantioselectivities
ranging from 11 to 60% ee. With these precedents in mind, we
therefore sought the desymmetrization of achiral cation 9. To
this end, reaction 9 with sodium bis[(-)-8-phenylmenthyl]
malonate26 gave the cyclohexenone (-)-27 as a single diaste-
reomer in excellent yield (Scheme 7). Luche reduction of (-)-
27 gave the equatorial cyclohexenol 28.27 Assignment of the
absolute stereochemistry at the carbinol carbon was based on
1
the H NMR chemical shifts of the alkenyl proton (H2) of the
derived (S)- and (R)-Mosher’s esters 29 and 30 (δ 5.41 and
5.33 ppm, respectively). These relative chemical shifts are
consistent with an (R)-stereochemical assignment at C1, and
therefore C5 is assigned as (S). This stereochemical assignment
was subsequently corroborated by X-ray crystal structure
analysis of 27.28 This route to chiral nonracemic 3-substituted-
4-methylcyclohexenones should be synthetically useful; notably
the cyclohexenone 31 (enantiomeric with 27 about the cyclo-
hexenone ring) was utilized in the synthesis of mevinolin and
compactin.29
1
Fe coordination as evidenced by two sets of signals in its H
and 13C NMR spectrum. Decomplexation of the mixture of
diastereomers 25h (or of 18h) with CAN gave the “free” diene
26 as a single product (eq 1). For reactions of the Fe(CO)2PPh3-
ligated cation 12, the electron donating ability of the phosphine
ligand increases the electron density on the pentadienyl ligand
and thus all reactions are frontier orbital controlled (i.e., attack
on the C1/C5 terminal carbons).
The diastereoselectivity for addition of the chiral malonate
to 9 is rationalized in the following fashion. Nucleophilic attack
occurs on the face of the pentadienyl ligand opposite to the Fe
metal and the malonate anion is oriented such that the π-system
of the nucleophile is synclinal with respect to the electrophilic
π-system (i.e., the C1-C2 bond) (Figure 3). Steric interaction
between the phenyl substitutent and the pentadienyl ligand
Previous efforts at the desymmetrization of achiral (cyclo-
hexadienyl)- and (cycloheptadienyl)iron(1+) cations by the
use of chiral phosphine ligands on iron11,25a or with chiral
nucleophiles such as sulfoximinyl acetates25b or N-acetyl- or
(26) Quinkert, G.; Schwartz, U.; Stark, H.; Weber, W. D.; Adam, F.;
Baier, H.; Frank, G.; Duerner, G. Liebigs Ann. Chem. 1982, 1999-2040.
(27) A similar reduction of chiral 4,5-disubstituted cyclohexenones
(prepared by nucleophilic addition/protonation of (arene)Cr(CO)3 complexes)
was previously reported: Pearson, A. J.; Gontcharov, A. V. J. Org. Chem.
1998, 63, 152-162.
(28) Bennett, D. W.; Siddiquee, T. A.; Haworth, D. T.; Chaudhury, S.;
Donaldson, W. A. J. Chem. Crystallogr. 2006, 36, 777-780.
(29) Clive, D. L. J.; Murthy, K. S. K.; Wee, A. G. H.; Prasad, J. S.; da
Silva, G. V. J.; Majewski, M.; Anderson, P. C.; Evans, C. F.; Haugen, R.
D.; Heerze, L. D.; Barrie, J. R. J. Am. Chem. Soc. 1990, 112, 3018-3028.
(25) (a) Howell, J. A. S.; Thomas, M. J. J. Chem Soc., Dalton Trans.
1983, 1401-1409. (b) Pearson, A. J.; Blystone, S. L.; Nar, H.; Pinkerton,
A. A.; Roden, B. A.; Yoon, J. J. Am. Chem. Soc. 1989, 111, 134-144. (c)
Pearson, A. J.; Khetani, V. D.; Roden, B. J. Org. Chem. 1989, 54, 5141-
5147. Notably, the greatest % ee’s were observed for addition to the (3-
+
methoxycyclohexadienyl)Fe(CO)3 cation.

5300 Organometallics, Vol. 26, No. 22, 2007
Chaudhury et al.
by column chromatography (SiO2, hexane-ethyl acetate ) 5:1 to
1:1 gradient) to afford 11 as a bright yellow oil (4.55 g, 91%): IR
(neat) 3379, 1969, 1907 cm-1; 1H NMR (CDCl3) δ 7.55-7.50 (m,
6H), 7.36 (br m, 9H), 4.20 (br m, 1H), 3.81 (br d, J ) 7.4 Hz, 2H),
2.15 (s, 3H), 1.64 (br m, 1H), 0.91 (m, 1H), 0.53 (br t, J ) 7.3 Hz,
1H), -0.13 (br t, J ) 8.6 Hz, 1H); 13C NMR (CDCl3) δ 214.5 (d,
JCP ) 22.3 Hz), 136.1 (d, JCP ) 38.9 Hz), 133.1 (d, JCP ) 10.8
Hz), 129.7 (d, JCP ) 2.3 Hz), 128.2 (d, JCP ) 9.2 Hz), 99.0, 86.5,
62.8, 56.2, 40.9, 14.4. This material was used in the next step
without further characterization. To an ice-cold solution of acetic
anhydride (5 mL) and hexafluorophosphoric acid (60% w/w
solution, 1.5 mL) was added an ice-cold solution of 11 (2.72 g,
5.76 mmol) and acetic anhydride (2.5 mL) in ether (35 mL). The
mixture was stirred for 30 min, during which time a bright yellow
precipitate formed. The mixture was added dropwise to a large
excess of ether (300 mL), and the resultant precipitate was collected
by vacuum filtration. The solid was washed with additional ether
and dried under high vacuum to afford 12 as a golden yellow solid
present in TS2 (see blue arrow) is expected to raise the energy
of this transition state compared to TS1.
In summary, nucleophilic attack on (3-methylpentadienyl)-
iron(1+) cation 9 or 12 generally occurs at a terminal (C1)
carbon to give (3-methyl-1,3-pentadiene)iron products. However
for stabilized nucleophiles such as malonate anions, attack at
either C1 or an internal (C2) carbon of the Fe(CO)3+-ligated
cation (9) is controlled by the nature of the counterion-
nucleophile association. The (pentenediyl)iron complexes formed
by attack at the C2 carbon eventually afford cyclohexenone
products as a result of CO insertion followed by reductive
elimination. Synthesis of the optically active cyclohexenone 27
was realized using bis[(-)-8-phenylmenthyl] malonate as the
nucleophile.
Experimental Section
All melting point measurements were carried out on a Mel-Temp
1
(3.23 g, 93%): mp 160-161 °C; IR (KBr) 2054, 2006 cm-1; H
1
apparatus and are uncorrected. All H and 13C NMR spectra were
NMR (CDCl3, 23 °C) δ 7.70-7.35 (m, 15H), 5.37 (br m, 2H),
2.37 (br s, 3H), 1.80 (br m, 2H), 1.47 (br m, 2H); 1H NMR (acetone-
d6, -70 °C) δ 7.72-7.65 (m, 15H), 6.07 (br t, J ) 10.8 Hz, 1H),
5.54 (dd, J ) 17.4, 10.3 Hz, 1H), 3.75 (br d, J ) 10.0 Hz, 1H),
2.52 (s, 3H), 2.45 (m, 1H), 1.63 (br m, 2H); 13C NMR (acetone-d6,
23 °C) δ 133.9 (d, JCP ) 11.3 Hz), 133.1 (d, JCP ) 3.0 Hz), 130.9,
130.4 (d, JCP ) 10.6 Hz), 116.4 (d, JCP ) 1.6 Hz), 101.5, 62.3,
22.2. Anal. Calcd for C26H24O2P2F6Fe: C, 52.02; H, 4.03. Found:
C, 51.80; H, 4.10.
recorded on either a Varian 300 Mercury+ or a Varian 400
UnityInova spectrometer. Elemental analyses were preformed by
Midwest Microlabs, Ltd., Indianapolix, IN. High-resolution mass
spectra were performed either at the Washington University
Resource for Mass Spectrometry or the Nebraska Center for Mass
Spectrometry.
Tricarbonyl(3-methylpentadienyl)iron(1+) Hexafluorophos-
phate (9). To an ice-cold solution of tricarbonyl(3-methyl-2,4-
pentadien-1-ol)iron (8)8 (0.700 g, 3.33 mmol) in ether (10 mL) and
acetic anhydride (1 mL) was added dropwise an ice-cold solution
of acetic anhydride (3 mL) and hexafluorophosphoric acid (60%
w/w solution, 1 g). The mixture was stirred for 15 min, during
which time a pale yellow precipitate formed. The mixture was added
dropwise to a large excess of ether (200 mL), and the resultant
precipitate was collected by vacuum filtration. The solid was washed
with additional ether and dried under high vacuum to afford 9 as
a pale yellow amorphous solid (0.926 g, 82%): mp 130-135 °C
(dec); IR (KBr) 2119, 2068 cm-1; 1H NMR (acetone-d6) δ 6.49 (t,
J ) 11.5 Hz, 2H), 3.81 (dd, J ) 10.1, 3.2 Hz, 2H), 2.87 (s, 3H),
2.44 (dd, J ) 12.6, 2.9 Hz, 2H); 13C NMR (acetone-d6, 23 °C) δ
117.9, 104.5, 64.2, 22.4 (the signal for the metal carbonyls not
observed). Anal. Calcd for C9H9O3PF6Fe: C, 29.53; H, 2.48.
Found: C, 29.32; H, 2.50.
Tricarbonyl(3-methyl-1,3Z-pentadiene)iron (18a). To a solu-
tion of iron cation 9 (0.200 g, 0.546 mmol) in dry THF (10 mL),
cooled to 0 °C, was added in one portion solid sodium cyanoboro-
hydride (0.056 g, 0.82 mmol). The reaction mixture was stirred at
0 °C for 30 min and then poured over a brine solution (10 mL).
The reaction mixture was extracted several times with ethyl acetate,
and the combined extracts were dried (MgSO4) and concentrated
under reduced pressure. The residue was purified by column
chromatography (SiO2, hexane-ethyl acetate ) 10:1) to afford 18a
1
as a yellow oil (0.079 g, 67%): IR (neat) 2043, 1963 cm-1; H
NMR (CDCl3) δ 5.32 (dt, J ) 8.5, 1.8 Hz, 1H), 2.72 (dq, J ) 7.3,
1.8 Hz, 1H), 2.16 (s, 3H), 1.68 (dd, J ) 7.6, 2.9 Hz, 1H), 1.30 (dd,
J ) 9.4, 2.9 Hz, 1H), 1.07 (d, J ) 7.3 Hz 3H); 13C NMR (CDCl3)
δ 211.5, 105.2, 89.8, 56.0, 37.4, 25.5, 13.7. The 13C NMR spectral
data for this product were identical with the literature values.15
Dicarbonyl(3-methylpentadienyl)(triphenylphosphine)iron-
(1+) Hexafluorophosphate (12). To a solution of tricarbonyl(ethyl
3-methyl-2E,4-pentadienoate)iron (7)8 (5.49 g, 19.6 mmol) in
acetone (130 mL) was added triphenylphosphine (5.66 g, 21.6
mmol), followed by trimethylamine N-oxide dihydrate (4.35 g, 39.2
mmol). The mixture as heated at reflux for 2 h, cooled to room
temperature, filtered through a pad of Celite, and concentrated. The
crude residue was purified by column chromatography (SiO2,
hexane-ethyl acetate ) 20:1 to 5:1 gradient) to afford 10 as a
bright golden-yellow semisolid (7.22 g, 77%): IR (neat) 1987, 1930,
Dicarbonyl(3-methyl-1,3Z-pentadiene)(triphenylphosphine)-
iron (25a). The reaction of iron cation 12 (0.200 g, 0.333 mmol)
with sodium cyanoborohydride (0.044 g, 0.698 mmol) was carried
out in a fashion similar to the preparation of 18a. The reaction
mixture was quenched by the addition of water (10 mL). The
resulting mixture was extracted several times with ethyl acetate,
and the combined organic extracts were dried (MgSO4) and
concentrated. The residue was purified by column chromatography
(alumina, hexane-ethyl acetate ) 10:1) to afford 25a as a yellow
oil (0.135 g, 90%): IR (neat) 1967, 1907 cm-1; 1H NMR (CDCl3)
δ 7.54-7.39 (m, 15H), 4.19 (m, 1H), 2.44 (q, J ) 7.1 Hz, 1H),
2.06 (s, 3H), 1.30 (m, 1H), 1.08 (br d, J ) 7.1 Hz 3H), 0.92 (t, J
) 7.5 Hz, 1H); 1H NMR (benzene-d6) 7.62 (m, 6H), 7.04 (m, 9H),
4.35 (m, 1H), 2.48 (dq, J ) 1.5, 7.1 Hz, 1H), 2.01 (s, 3H), 1.33
(dt, J ) 1.3, 8.4 Hz, 1H), 1.15 (m, 1H), 1.11 (d, J ) 3.1 Hz, 3H);
1
1701 cm-1; H NMR (CDCl3, 70 °C) δ 7.58 (br t, J ) 8.6 Hz,
6H), 7.05-7.03 (m, 9H), 4.43 (br t, J ) 7.6 Hz, 1H), 4.00 (m,
2H), 2.61 (s, 3H), 1.29 (m, 1H), 1.02 (t, J ) 7.2 Hz, 3H), 0.42 (s,
1H), -0.15 (m, 1H); 13C NMR (CDCl3) δ 212.8 (d, JCP ) 18.9
Hz), 173.7, 135.5 (d, JCP ) 40.1 Hz), 133.2 (d, JCP ) 10.9 Hz),
129.9, 128.3 (d, JCP ) 9.8 Hz), 101.2, 88.4, 59.6, 42.8, 31.9, 18.9,
14.5. This material was used in the next step without further
characterization. To a solution of 10 (5.44 g, 10.6 mmol) in CH2-
Cl2 (160 mL), cooled in a dry ice/acetone bath, was added, via
syringe, a solution of DIBAL in hexanes (1.0 M, 32.0 mL, 32.0
mmol). The reaction mixture was stirred at -78 °C for 90 min.
After this time, methanol (15 mL) was added, followed by water.
The layers were separated, and the aqueous layer was extracted
several times with CH2Cl2. The combined organic extracts were
dried (MgSO4) and concentrated. The crude residue was purified
13C NMR (CDCl3) δ 214.9 (d, JCP ) 22.5 Hz) 136.5 (d, JCP
)
39.0 Hz), 133.2 (d, JCP ) 12.5 Hz), 129.5, 128.2 (d, JCP ) 9.7
Hz), 101.7, 92.8, 48.3, 39.3, 24.2, 13.9. Anal. Calcd for C26H25O2-
PFe: C, 68.44; H, 5.52. Found: C, 68.59; H, 5.83.
Tricarbonyl(3-methyl-1,3Z-hexadiene)iron (18b). To a suspen-
sion of CuBr-SMe2 (0.210 g, 1.03 mmol) in THF (20 mL) at
-78 °C was added a solution of methyl lithium in ether (1.6 M,
1.3 mL, 2.0 mmol), and mixture was stirred at -78 °C for 1 h.
Solid cation 9 (0.300 g, 0.820 mmol) was added and the mixture

(3-Methylpentadienyl)iron(1+) Cations
Organometallics, Vol. 26, No. 22, 2007 5301
stirred at -78 °C for an additional 1 h. The mixture was warmed
to room temperature, diluted with saturated aqueous NH4Cl (15
mL) and water (15 mL), and extracted several times with ether.
The combined organic extracts were dried (MgSO4) and concen-
trated. The residue was purified by column chromatography (SiO2,
hexane-ethyl acetate ) 10:1) to afford 18b as a yellow oil (0.118
g, 61%): IR (neat) 2042, 1962 cm-1; 1H NMR (CDCl3) δ 5.33 (t,
J ) 8.2 Hz, 1H), 2.59 (t, J ) 6.9 Hz, 1H), 2.17 (s, 3H), 1.69 (dd,
J ) 7.3, 2.3 Hz, 1H), 1.49 (pentet, J ) 7.0 Hz, 1H), 1.27 (dd, J )
9.2, 2.2 Hz, 1H), 1.16 (pentet, J ) 7.2 Hz, 1H), 0.95 (t, J ) 7.3
Hz, 3H); 13C NMR (CDCl3) δ 211.5, 103.9, 90.3, 65.3, 37.4, 26.1,
22.1, 17.8. A satisfactory elemental analysis was not obtained for
this compound, and purity was assessed on the basis of NMR
spectroscopy.
was stirred at room temperature for 1 h. After this time, water (10
mL) was added and the mixture was extracted several times with
CH2Cl2. The combined extracts were washed with brine, dried
(MgSO4), and concentrated. The residue was purified by column
chromatography (SiO2, hexane-ethyl acetate ) 5: 1) to afford 19d
as a golden yellow liquid (70 mg, 88%): IR (neat) 2043, 1960
1
cm-1; H NMR (CDCl3) δ 7.34 (m, 1H), 6.31 (dd, J ) 3.2, 1.9
Hz, 1H), 6.05 (d, J ) 3.2 Hz, 1H), 5.17 (t, J ) 8.2 Hz, 1H), 3.10
(dd, J ) 16.1, 6.8 Hz, 1H), 2.96 (dd, J ) 16.1, 7.3 Hz, 1H), 2.23
(s, 3H), 1.60 (dd, J ) 6.9, 2.6 Hz, 1H), 1.08 (t, J ) 7.3 Hz, 1H),
0.18 (dd, J ) 9.0, 2.7 Hz, 1H); 13C NMR (CDCl3) δ 211.6, 154.7,
141.2, 110.3, 105.4, 102.7, 82.9, 60.8, 37.1, 29.7, 18.8; FAB-HRMS
m/z 288.0091 (calcd for C13H12O4Fe m/z 288.0085).
Tricarbonyl(5-methoxy-3-methyl-1,3Z-pentadiene)iron (18e)
and tricarbonyl(5-methoxy-3-methyl-1,3E-pentadiene)iron (19e).
To methanol (10 mL) was added solid cation 9 (100 mg, 0.273
mmol) followed by three drops of triethylamine. The reaction
mixture was stirred at room temperature for 90 min. Saturated
aqueous ammonium chloride (15 mL) and water (10 mL) were
added, and the resulting mixture was extracted several times with
CH2Cl2. The combined organic extracts were dried (MgSO4) and
concentrated. Purification of the residue by column chromatography
(SiO2, hexane-ethyl acetate ) 5:1) gave a brown oil (0.193 g,
90%), which was determined to be a mixture of Z-18e and E-19e
(2:5) by 1H NMR spectroscopy: IR (neat) 2045, 1962 cm-1. Anal.
Calcd for C10H12O4Fe: C, 47.65; H, 4.80. Found: C, 48.00; H,
4.79.
Dicarbonyl(3-methyl-1,3Z-hexadiene)(triphenylphosphine)-
iron (25b). The reaction of 12 (0.200 g, 0.333 mmol) with MeLi/
CuBr-SMe2 was carried out in a fashion similar to the preparation
of 18b. The residue was purified by column chromatography (Al2O3,
hexane-ethyl acetate ) 10:1) to afford 25b as a waxy solid (0.120
1
g, 77%): IR (neat) 1967, 1907 cm-1; H NMR (CDCl3) δ 7.51-
7.37 (m, 15H), 4.09 (m, 1H), 2.25 (br t, J ) 7.1 Hz, 1H), 2.03 (s,
3H), 1.99 (m, 1H), 1.51 (m, 1H), 1.26 (m, 1H), 1.11 (t, J ) 7.8
Hz, 3H), 0.92 (m, 1H); 1H NMR (benzene-d6) δ 7.62 (m, 6H), 7.00
(m, 9H), 4.27 (dd, J ) 7.9, 8.1 Hz, 1H), 2.42 (br t, J ) 7.1 Hz,
1H), 2.02 (s, 3H), 1.70 (m, 1H), 1.36 (dt, J ) 2.6, 8.4 Hz, 1H),
1.23-1.14 (m, 2H), 0.99 (t, J ) 7.3 Hz, 3H); 13C NMR (CDCl3)
δ 215.2, 136.5 (d, JCP ) 37.6 Hz), 133.2 (d, JCP ) 10.9 Hz), 129.5,
128.2 (d, JCP ) 9.3 Hz), 100.4, 93.2, 58.0 (JCP ) 10.1 Hz), 39.4
(d, JCP ) 6.3 Hz), 24.8, 22.3, 18.0 (d, JCP ) 2.4 Hz). Anal. Calcd
for C27H27O2PFe: C, 68.95; H, 5.78. Found: C, 69.07; H, 5.88.
1
Z-18e: H NMR (CDCl3) 5.40 (t, J ) 8.5 Hz, 1H), 3.48 (m,
2H), 3.22 (s, 3H), 2.89 (t, J ) 10.1 Hz, 1H), 2.67 (dd, J ) 5.4, 9.4
Hz, 1H) 2.22 (s, 3H), 1.17 (dd, J ) 7.4, 15.7 Hz, 1H); 13C NMR
(CDCl3) 104.5, 71.3, 58.8, 58.7, 58.3, 36.4, 25.5.
Reaction of 9 with Triphenylphosphine (18c). To a solution/
suspension of 9 (0.114 g, 0.311 mmol) in CH2Cl2 (10 mL) was
added triphenylphosphine (0.086 g, 0.328 mmol). The suspension
rapidly dissolved, and the golden yellow solution was stirred for
30 min. The reaction mixture was concentrated. The golden yellow
sticky residue was triturated with ether which made the solution
cloudy. After standing overnight in the refrigerator, 18c was
collected as golden yellow crystalline solid (0.159 g, 81%): mp
175-177 °C; IR (KBr) 2059, 1975 cm-1; 1H NMR (acetone-d6) δ
7.97-7.83 (m, 15 H), 5.62 (t, J ) 8.8 Hz, 1H), 4.00 (dt, J ) 14.6,
3.2 Hz, 1H), 3.40 (m, 1H), 2.90 (br d, J ) 10.1 Hz, 1H), 2.67 (br
t, J ) 12.6 Hz, 1H), 1.85 (dd, J ) 9.8, 3.6 Hz, 1H), 1.77 (s, 3H);
13C NMR (acetone-d6) δ 210.9, 136.4 (d, JCP )3.1 Hz), 135.2 (d,
JCP ) 10.2 Hz), 131.6 (d, JCP ) 12.7 Hz), 119.6 (d, JCP ) 83.8
Hz), 105.3, 93.9, 47.6 (d, JCP ) 10.1 Hz), 40.4 (d, JCP ) 1.8 Hz),
25.5, 25.4 (d, JCP ) 41.7 Hz). Anal. Calcd for C27H24O3P2F6Fe:
C, 51.61; H, 3.86. Found: C, 51.49; H, 3.86.
1
E-19e: H NMR (CDCl3) δ 5.14 (t, J ) 7.9 Hz, 1H), 3.56 (dd,
J ) 10.1, 5.6 Hz, 1H), 3.49 (dd, J ) 10.1, 8.4 Hz, 1H), 3.34 (s,
3H), 2.17 (s, 3H), 1.64 (dd, J ) dd, 7.0, 2.7 Hz, 1H), 0.92 (dd, J
) 8.4, 6.2 Hz, 1H), 0.26 (dd, J ) 9.3, 2.6 Hz, 1H); 13C NMR
(CDCl3) δ 211.2, 103.3, 83.6, 71.4, 58.5, 37.6, 18.3.
Reaction of 9 with Lithium Dimethyl Malonate (18f). To an
ice cold stirring solution of dimethyl malonate (0.326 g, 2.47 mmol)
in THF (10 mL) was added a solution of n-butyllithium in hexanes
(2.5 M, 1.0 mL, 2.5 mmol), and the mixture was stirred for 30
min. The generated dimethyl malonate anion was then transferred
to an ice-cold solution of cation 9 (0.500 g, 1.37 mmol) in THF
(25 mL). The reaction mixture was stirred at 0 °C for 1 h. The
reaction mixture was warmed to room temperature, and then water
(20 mL) was added. The mixture was extracted several times with
ether, and the combined extracts were dried (MgSO4) and concen-
trated. The residue was purified by column chromatography (SiO2,
hexane-ethyl acetate ) 10:1) to afford 18f as a golden yellow
liquid (0.380 g, 80%): IR (neat) 2046, 1966, 1736 cm-1; 1H NMR
(CDCl3) δ 5.33 (br t, J ) 8.4 Hz, 1H), 3.71 (s, 3H), 3.70 (s, 3H),
3.29 (dd, J ) 8.8, 6.1 Hz, 1H), 2.40 (ddd, J ) 10.5, 4.2, 1.5 Hz,
1H), 2.17 (m, 1H), 2.09 (s, 3H), 1.73 (dd, J ) 7.6, 3.3 Hz, 1H),
1.61 (ddd, J ) 14.3, 10.4, 8.9 Hz, 1H), 1.28 (dd, J ) 9.2, 3.2 Hz,
1H); 13C NMR (CDCl3) δ 210.6, 169.1, 168.9, 104.2, 90.8, 57.1,
54.3, 52.8, 52.7, 37.7, 29.0, 25.7. Anal. Calcd for C14H16O7Fe: C,
47.75; H, 4.59. Found: C, 48.01; H, 4.78.
Reaction of 12 with Triphenylphosphine (25c). The reaction
of 12 (0.100 g, 0.167 mmol) in CH2Cl2 (6 mL) with triphenylphos-
phine was carried out in a fashion similar to the preparation of
18c. After stirring of the solution for 20 h, the solvent was
evaporated and the residue was taken up in a minimal amount of
CH2Cl2 (1 mL) and triturated with ether until the solution became
cloudy. After standing for 1 h, 25c was collected as golden yellow
crystalline solid (128 mg, 89%): mp 120-123 °C; 1H NMR
(CDCl3) δ 7.81 (dt, J ) 1.8, 7.8 Hz, 3H), 7.70 (dt, J ) 3.3, 7.8
Hz, 6H), 7.57 (dd, J ) 7.5, 12.3 Hz, 6H), 7.48-7.34 (m, 15H),
4.34-4.05 (br s, 1H), 3.30-3.08 (br s, 1H), 2.78-2.60 (br m, 1H),
1.92-1.79 (m, 1H), 1.76-1.66 (br s, 1H), 1.48 (s, 3H), 1.48-1.36
(br m, 1H); 13C NMR (CDCl3) δ 135.0 (d, JCP ) 2.9 Hz), 134.4
(d, JCP ) 39.4 Hz), 133.0 (d, JCP ) 9.1 Hz), 129.8 (d, JCP ) 1.7
Hz), 128.2 (d, JCP ) 9.7 Hz), 117.6 (d, JCP ) 82.9 Hz), 99.7, 95.5
(br), 66.1, 41.6, 24.0, 16.0. Anal. Calcd for C44H39O2P3F6Fe·2/
3H20: C, 60.43; H, 4.65. Found: C, 60.46; H, 4.62.
Reaction of 9 with Sodium Dimethyl Malonate (20f). To an
ice cold stirring suspension of NaH (0.037 g, 0.923 mmol) in dry
THF (10 mL) was added dimethyl malonate (0.081 g, 0.615 mmol).
The mixture was stirred at 0 °C for 10 min, and then solid cation
9 (0.150 g, 0.410 mmol) was added in one portion and the reaction
mixture was stirred for 2 h at room temperature. During this time
a yellow-brown turbidity began to appear. The reaction mixture
was diluted with CH2Cl2, a saturated solution of methanolic
NaHCO3 (20 mL) was added, and this mixture was stirred overnight
at room temperature. Water (20 mL) was added, and the mixture
was extracted several times with CH2Cl2. The combined extracts
Tricarbonyl[5-(2′-furyl)-3-methyl-1,3E-pentadiene]iron (19d).
To a solution of 9 (100 mg, 0.273 mmol) in CH2Cl2 (10 mL) was
added excess furan (0.372 g, 5.46 mmol). The reaction mixture

5302 Organometallics, Vol. 26, No. 22, 2007
Chaudhury et al.
were dried (MgSO4) and concentrated. The residue was purified
by column chromatography (SiO2, hexane-ethyl acetate ) 5:1) to
afford 20f as a light yellow liquid (0.090 g, 91%): IR (neat) 1734,
The mixture was stirred at 0 °C for 10 min. Solid cation 12 (0.200
g, 0.333 mmol) was added to the malonate anion solution in one
portion, and the reaction mixture was stirred at room temperature
for 1 h. Water (20 mL) was added, and the reaction mixture was
stirred for an additional 10 min and then extracted several times
with ethyl acetate. The combined extracts were dried (MgSO4) and
concentrated. The residue was purified by column chromatography
(SiO2, hexane-ethyl acetate ) 10:1) to afford 25f as a golden
yellow liquid (0.181 g, 93%): IR (neat) 1973, 1912 cm-1; 1H NMR
(C6D6, 50 °C) δ 7.56-7.49 (m, 6H), 6.05-6.93 (m, 9H), 4.27 (dt,
J ) 8.1, 4.5 Hz, 1H), 3.38 (dd, J ) 8.1, 6.1 Hz, 1H), 3.33 (s, 3H),
3.31 (s, 3H), 2.49 (m, 1H), 2.35 (dd, J ) 10.0, 2.3 Hz, 1H), 2.03
(s, 3H), 1.92 (m, 1H), 1.32 (dt, J ) 8.5, 3.2 Hz, 1H), 1.13 (m,
1
1676 cm-1; H NMR (C6D6) δ 6.11 (dd, J ) 10.1, 6.1 Hz, 1H),
5.81 (d, J ) 10.1 Hz, 1H), 3.31 (d, J ) 10.9 Hz, 1H), 3.23 (s, 3H),
3.20 (s, 3H), 3.03 (m, 1H), 2.47 (dd, J ) 16.7, 3.8 Hz, 1H), 2.31
(m, 1H), 2.10 (dd, J ) 16.7, 13.5 Hz, 1H), 0.55 (d, J ) 7.4 Hz,
3H); 13C NMR (C6D6) δ 195.6, 167.9, 167.8, 153.5, 127.9, 54.6,
52.2, 52.1, 37.5, 37.3, 31.6, 12.2; FAB-HRMS m/z 247.1148 (calcd
for C12H16O5Li m/z 247.1158).
Reaction of 9 with Lithium Dimethyl Malonate/12-Crown-4
(20f). To a solution lithium dimethyl malonate in THF [freshly
prepared from dimethyl malonate (0.216 g, 1.64 mmol) and
butyllithium] was added 12-crown-4 (0.440 g, 2.50 mmol), and the
resultant solution stirred for 15 min. To this solution was added
solid cation 9 (0.300 g, 0.820 mmol). The reaction mixture was
worked up in a fashion similar to that for the reaction of 9 with
sodium dimethyl malonate. Purification by column chromatography
(SiO2, hexane-ethyl acetate ) 5:1) gave 20f (0.165 g, 84%), which
1H); 13C NMR (C6D6) δ 211.5 (d, JCP ) 6 Hz), 214.8 (d, JCP
)
22.5), 169.3, 169.1, 137.6 (d, JCP ) 37.5 Hz), 133.4 (d, JCP ) 15.0
Hz), 129.7, 128.5, 101.0, 94.4, 55.0, 52.0, 51.9, 50.7, 39.8, 29.9,
24.6. Anal. Calcd for C31H31O6PFe: C, 63.49; H, 5.34. Found: C,
63.78; H, 5.64.
Reaction of 12 Cation with Sodium Ethyl 2-Oxocyclohexan-
ecarboxylate (25h). To an stirring suspension of NaH (0.030 g,
0.75 mmol) in dry THF (20 mL) under N2 at 0 °C was added ethyl
2-cyclohexanonecarboxylate (0.100 g, 0.592 mmol). The mixture
was stirred at 0 °C for 1 h, and then solid cation (0.535 g, 0.888
mmol) was added in one portion. The mixture was stirred for 3 h
at 23 °C and then diluted with water (20 mL). The mixture was
extracted several times with ethyl acetate, and the combined extracts
were dried (MgSO4) and concentrated. The residue was purified
by column chromatography (SiO2, hexane-ethyl acetate ) 10:1)
to afford 25h as a golden yellow waxy solid (0.321 g, 87%). This
was determined to be a mixture of diastereomers (1:1.6 by 1H NMR
1
was identified by comparison of its H NMR spectral data with
those previously obtained.
Reaction of 9 with Sodium Dimethyl Malonate/ZnCl2 (18f).
A solution sodium dimethyl malonate in THF [freshly prepared
from dimethyl malonate (0.072 g, 0.55 mmol) and sodium hydride]
was transferred by cannula to a flask containing anhydrous ZnCl2
(0.148 g, 1.09 mmol). A white turbidity immediately appeared. The
reaction mixture was stirred at 0 °C for 30 min, and then solid
cation 9 (100 mg, 0.272 mmol) was added in one portion. The
reaction mixture was stirred for 2 h at room temperature and worked
up in a fashion similar to that for the reaction of 9 with lithium
dimethyl malonate. Purification by column chromatography (SiO2,
hexane-ethyl acetate ) 10:1) gave 18f (70 mg, 63%), which was
spectroscopy): mp 124-126 °C; IR (neat) 1969, 1905, 1708 cm-1
;
1H NMR (C6D6, 50 °C) δ 7.67-7.57 (m, 6H), 7.06-6.99 (m, 9H),
4.27 (m, 1H), 3.94 (m, 2H), 2.50 (m, 3H), 2.27 (m, 2H), 2.18 and
2.14 (2 × s, 3H total), 2.03 (m, 2H), 1.50 (m, 4H), 1.20 (m, 2H),
0.98 and 0.91 (2 × t, J ) 7.1 Hz, 3H total); 13C NMR (C6D6) δ
206.0 [205.7], 171.8 [171.4], 136.6 (JCP ) 38.5 Hz), 133.3 (d, JCP
) 11.3 Hz), 129.6 (JCP ) 2.0 Hz), 128.3 (JCP ) 9.0 Hz), 102.3
[102.2], 94.2 [93.9], 62.9 [62.8], 61.0 [60.9], 48.6 [48.4], 41.5
[41.3], 39.8, 36.0 [35.9], 35.8 [35.3], 27.8 [27.7], 25.1 [24.7], 22.7
[22.6], 14.2 [14.1], diastereomeric signals in brackets. Anal. Calcd
for C35H37O5PFe: C, 67.32; H, 5.97. Found: C, 67.34; H, 6.01.
1
identified by comparison of its H NMR spectral data with those
previously obtained.
Reaction of 9 with Lithium Dimethyl Methylmalonate (18g).
The reaction of cation 9 (0.200 g, 0.546 mmol) with lithium
dimethyl methylmalonate was carried out in a fashion similar to
the reaction of 9 with lithium dimethyl malonate. Purification of
the residue by column chromatography (SiO2, hexane-ethyl acetate
) 10:1) gave 18g as a golden yellow liquid (0.090 g, 45%): IR
(neat) 2046, 1969, 1734 cm-1; 1H NMR (CDCl3) δ 5.32 (br t, J )
8.6 Hz, 1H), 3.72 (s, 3H), 3.69 (s, 3H), 2.28 (dd, J ) 14.2, 3.7 Hz,
1H), 2.13 (m, 1H), 1.72 (dd, J ) 7.7, 3.5 Hz, 1H), 1.53 (dd, J )
14.1, 11.4 Hz, 1H), 1.37 (s, 3H), 1.29 (dd, J ) 9.4, 3.2 Hz, 1H);
13C NMR (CDCl3) δ 210.9, 172.4, 172.3, 105.2, 90.5, 55.4, 55.1,
52.8, 52.6, 37.8, 36.0, 25.8, 20.0. A satisfactory elemental analysis
was not obtained for this compound, and purity was assessed on
the basis of NMR spectroscopy.
Reaction of 9 with Sodium Ethyl 2-Oxocyclohexanecarboxy-
late (18h). The reaction of 9 (0.240 g, 0.710 mmol) with sodium
2-cyclohexanonecarboxylate was carried out in a fashion similar
to the reaction of 12 with this nucleophile. After the usual workup,
the residue was purified by column chromatography (SiO2, hexane-
ethyl acetate ) 10:1) to afford 18h as a brown oil (0.179 g, 78%).
This was determined to be a mixture of diastereomers (1:1.2 by 1H
1
NMR spectroscopy): IR (neat) 2044, 1966, 1713 cm-1; H NMR
Reaction of 9 with Sodium Dimethyl Methylmalonate (18g,
20g). The reaction of cation 9 (0.200 g, 0.546 mmol) with sodium
dimethyl methylmalonate was carried out in a fashion similar to
the reaction of 9 with sodium dimethyl malonate. Purification of
the residue by column chromatography (SiO2, hexane-ethyl acetate
) 5:1) gave 18g (0.070 g, 34%) as an oil followed by 20g (0.076
g, 55%) as a light yellow liquid. The diene complex 18g was
(C6D6, 50 °C) δ 4.76 (t, J ) 8.3 Hz, 1H), 3.84 (m, 2H), 2.45 (m,
3H), 2.08 (m, 2H), 1.92 and 1.85 (2 × s, 3H total), 1.80 (m, 3H),
1.47 (m, 1H), 1.35 (m, 2H), 1.22 (m, 1H), 1.13 (m, 2H), 0.88 (t, J
) 7.2 Hz, 3H); 13C NMR (d6-acetone) δ 211.8, 206.1 [206.0], 171.8
[171.4], 106.0 [105.8], 90.6 62.9 [62.8], 61.5 [61.4], 57.2 [56.7],
41.6 [41.5], 38.2 [38.0], 36.7, 35.9 [35.7], 28.0 [27.9], 26.0 [25.8],
23.1 [22.9], 14.4 [14.3], diastereomeric signals in brackets. Anal.
Calcd for C18H22O6Fe: C, 55.39; H, 5.69. Found: C, 55.70; H,
5.70.
1
identified by comparison of its H NMR spectral data with that
1
previously obtained. 20g: IR (neat) 2956, 1731, 1681 cm-1; H
NMR (C6D6) δ 6.20 (dd, J ) 10.1, 6.1 Hz, 1H), 5.86 (d, J ) 10.1
Hz, 1H), 3.26 (s, 3H), 3.21 (s, 3H), 3.00 (dt, J ) 14.1, 4.1 Hz,
1H), 2.72 (dd, J ) 16.3, 4.1 Hz, 1H), 2.57 (dd, J ) 16.3, 14.4 Hz,
1H), 2.12 (m, 1H), 1.32 (s, 3H), 0.68 (d, J ) 7.1 Hz, 3H); 13C
NMR (C6D6) δ 197.6, 171.6, 171.5, 153.8, 127.6, 56.0, 52.0, 51.9,
41.3, 37.1, 31.8, 18.9, 12.0; FAB-HRMS m/z 261.1313 (calcd for
C13H18O5Li m/z 261.1314).
Ethyl 1-(3-Methyl-2Z,4-pentadienyl)cyclohexanecarboxylate
(26). To a solution of 18h (0.179 g, 0.460 mmol) in methanol (10
mL) was added cerium(IV) ammonium nitrate (0.126 g, 2.3 mmol)
in small portions. Monitoring of the reaction by TLC indicated the
reaction to be complete after 30 min. Water (10 mL) was added,
the resulting mixture was extracted several times with ether, and
the combined extracts were dried (MgSO4) and concentrated. The
residue was purified by column chromatography (SiO2, hexane-
ethyl acetate ) 10:1) to afford 26 as a colorless oil (0.060 g, 55%).
Reaction of 12 with Sodium Dimethyl Malonate (25f). To an
ice cold stirring suspension of NaH (0.030 g, 0.748 mmol) in dry
THF (10 mL) was added dimethyl malonate (0.089 g, 0.680 mmol).

(3-Methylpentadienyl)iron(1+) Cations
Organometallics, Vol. 26, No. 22, 2007 5303
Decomplexation of 25h (0.310 g, 0.451 mmol) under similar
reaction conditions gave, after chromatographic purification, 26 (83
mg, 77%): IR (neat) 3055, 1712, 1266 cm-1; 1H NMR (CDCl3) δ
6.73 (dd, J ) 10.8, 17.1 Hz, 1H), 5.35 (t, J ) 8.3 Hz, 1H), 5.22 (d,
J ) 17.0 Hz), 5.10 (d, J ) 10.7 Hz, 1H), 4.16 (q, J ) 7.1 Hz, 2H),
2.75 (dd, J ) 7.8, 14.7 Hz, 1H), 2.56-2.43 (m, 3H), 2.04 (m, 3H),
1.82 (s, 3H), 1.80-1.40 (m, 6H), 1.25 (t, J ) 7.0 Hz, 3H); 13C
NMR (CDCl3) δ 206.7, 170.7, 134.8, 132.9, 124.4, 114.1, 61.6,
61.5, 41.7, 36.4, 32.9, 28.2, 23.2, 20.8, 14.9. The purity of this
compound was assessed on the basis of NMR spectroscopy.
(m & s, 4H); 13C NMR (CDCl3, partial) δ 206.0, 168.1, 131.8,
130.2, 49.8, 43.6, 39.4, 20.5.
Reaction of 12 with Potassium Phthalimide (25j). The reaction
of 12 (0.100 g, 0.167 mmol) with potassium phthalimide was carried
out in a fashion similar to the reaction of 9 with potassium
phthalimide. Purified by column chromatography (SiO2, hexane-
ethyl acetate ) 10:1) gave 25j as a golden yellow waxy solid (0.100
1
g, 99%): IR (neat) 1975, 1916 cm-1; H NMR (C6D6, 50 °C) δ
7.57-7.49 (m, 8H), 6.96-6.94 (m, 7H), 6.89-6.86 (m, 4H), 4.33
(brm, 1H), 3.94 (dd, J ) 14.2, 6.4 Hz, 1H), 3.31 (dd, J ) 14.2, 9.2
Hz, 1H), 2.87 (t, J ) 7.1 Hz, 1H), 1.94 (s, 3H), 1.79 (m, 1H), 1.28
(m, 1H); 13C NMR (C6D6) δ 168.4, 136.7 (d, JCP ) 40 Hz), 133.8
(d, JCP ) 10.5 Hz), 133.6, 133.3, 130.1, 128.8, 123.3, 100.5, 95.3,
37.7, 32.2, 24.2, 14.7. Anal. Calcd for C34H28NO4PFe: C, 67.89;
H, 4.70; N, 2.33. Found: C, 67.74; H, 5.00; N, 2.45.
Reaction of 9 with Lithium Methyl Cyclohexanecarboxylate
(20i). To a cold (-78 °C), magnetically stirring solution of
diisopropylamine (0.070 g, 0.69 mmol) in dry THF (3 mL) under
N2 was slowly added a solution of n-butyl lithium (2.5 M in
hexanes, 0.3 mL 0.7 mmol) and stirred for 10 min. To the LDA
solution was added methyl cyclohexanecarboxylate (0.071 g, 0.50
mmol), and the mixture was stirred for an additional 30 min at
-78 °C. Solid cation 9 (0.183 g, 0.500 mmol) was added to the
anion solution in one portion, and the reaction mixture was stirred
for 1 h at -78 °C and then 1 h at room temperature. During this
time a yellow turbidity began to appear. The reaction mixture was
quenched with 1 M HCl solution (10 mL) and then extracted several
times with ether. The combined organic extracts were dried
(MgSO4) and concentrated. The residue was purified by column
chromatography (SiO2, hexanes-ethyl acetate ) 10:1) to afford
an inseparable mixture (6:1 ratio) of 2- and 3-cyclohexenones 20i/
20i′ (0.100 g, 80%): IR (neat) 2941, 2858, 1724, 1678 cm-1. 20i
(2-cyclohexenone): 1H NMR (CDCl3) δ 6.91 (dd, J ) 10.1, 6.4
Hz, 1H), 5.86 (d, J ) 10.1 Hz, 1H), 3.68 (s, 3H), 2.59 (m, 1H),
2.50 (m, 1H), 2.20 (m, 1H), 2.11 (m, 1H), 1.59 (m, 3H), 1.24 (m,
5H), 1.01 (d, J ) 7.1 Hz, 3H); 13C NMR (CDCl3) δ 200.8, 176.0,
156.8, 127.3, 51.8, 42.9, 46.0, 35.6, 33.0, 32.7, 32.4, 25.8, 23.6,
23.3, 12.3. 20i′: 1H NMR (CDCl3, partial) δ 5.62 (m, 1H), 3.60
(s, 3H), 2.70 (m, 1H), 1.78 (br s, 3H); 13C NMR (CDCl3, partial)
δ 211.1, 135.5, 123.2, 52.7, 51.7, 49.3, 41.8, 39.5, 32.5, 32.3, 25.6,
25.5, 23.8, 23.6; FAB-HRMS m/z 257.1735 (calcd for C15H22O3Li
m/z 257.1729).
Reaction of 9 with Sodium Bis[(-)-8-phenylmenthyl] Mal-
onate (27). The reaction of cation 9 (0.200 g, 0.546 mmol) with
sodium bis[(-)-8-phenylmenthyl] malonate was carried out in a
fashion similar to the reaction of 9 with sodium dimethyl malonate.
Purification of the residue by column chromatography (SiO2,
hexane-ethyl acetate ) 5:1) gave 27 (0.190 g, 95%) as an off-
white foam. Recrystallization from CH3CN/H2O gave a crystalline
solid: mp 52-55 °C; [R]20365 ) -12 (c 0.20, hexanes); [R]20
)
589
-25 (c 0.20, hexanes); IR (neat) 3055, 1742, 1676 cm-1; 1H NMR
(CDCl3) δ 7.31 (m, 4H), 7.25 (m, 4H), 7.16 (m, 2H), 6.95 (dd, J
) 10.1, 6.0 Hz, 1H), 5.95 (d, J ) 10.1 Hz, 1H), 4.91 (dt, J ) 10.8,
4.4 Hz, 1H), 4.82 (dt, J ) 8.3, 4.3 Hz, 1H), 2.87 (d, J ) 11.3 Hz,
1H), 2.72 (m, 2H), 2.15 (d, J ) 9.1 Hz, 2H), 2.04-1.50 (m, 10H),
1.43 (s, 3H), 1.37 (s, 3H), 1.27 (s, 3H), 1.23-0.93 (m, 9H), 0.97
(d, J ) 7.4 Hz, 3H), 0.89 (d, J ) 6.7 Hz, 3H), 0.88 d, J ) 7.2 Hz,
3H); 13C NMR (CDCl3) δ 197.9, 168.1, 166.9, 155.6, 151.2, 150.6,
128.3, 128.2, 125.8, 54.7, 50.4, 41.5, 41.4, 40.3, 40.2, 36.8, 35.9,
34.8, 25.4, 24.7, 22.8, 22.0, 14.3, 12.6. Anal. Calcd for C42H56O5:
C, 78.70; H, 8.82. Found: C, 78.67; H, 8.91.
Reduction of Chiral Cyclohexenone (28). To a solution of 27
(150 mg, 0.234 mmol) in methanol (10 mL) was added cerium-
(III) chloride (87 mg, 0.23 mmol) and sodium borohydride (28 mg,
0.74 mmol). The reaction mixture was stirred for 30 min at room
temperature and then quenched with water. The resultant mixture
was extracted several times with CH2Cl2, and the combined extracts
were washed with saturated aqueous NaHCO3, dried (MgSO4), and
concentrated. The residue was purified by column chromatography
(SiO2, hexane-ethyl acetate ) 5:1) to afford 28 as a light yellow
oil (103 mg, 69%): 1H NMR (CDCl3) δ 7.33 (m, 4H), 7.31 (m,
4H), 7.17 (m, 2H), 5.72 (ddd, J ) 10.1, 5.9, 1.7 Hz, 1H), 5.60 (d,
J ) 10.1 Hz, 1H), 4.88 (m, 2H), 4.27 (br t, J ) 8.0 Hz, 1H), 2.98
(d, J ) 10.6 Hz, 1H), 2.53 (m, 2H), 2.09-1.83 (m, 10H), 1.74 (m,
2H), 1.48 (s, 3H), 1.37 (s, 3H), 1.31 (s, 3H), 1.26 (s, 3H), 1.23-
0.93 (m, 6H), 0.89 (m, 9H); 13C NMR (CDCl3) δ 168.9, 167.2,
150.9, 150.6, 134.8, 129.6, 128.3, 128.2, 125.9, 125.8, 125.6, 125.5,
68.2, 55.6, 50.7, 50.5, 41.7, 41.4, 40.6, 40.4, 35.3, 34.6 (two
signals), 31.8, 31.6, 31.5, 30.9, 30.7, 30.6, 29.9, 27.6, 27.4, 24.1,
23.8, 22.9, 22.0, 15.0, 14.3; FAB-HRMS m/z 649.4443 (calcd for
C42H58O5Li m/z 649.4444).
Reaction of 9 Cation with Potassium Phthalimide (18j, 20j).
To a stirring solution of cation 9 (0.300 g, 0.820 mmol) in THF
(20 mL) under N2 at 0 °C was added solid potassium phthalimide
(0.228 g, 1.23 mmol) in one portion. The reaction mixture was
stirred at room temperature for 30 min and then poured into a
saturated solution of ammonium chloride (15 mL) and water (10
mL). The mixture was extracted several times with ethyl acetate,
and combined organic extracts were washed with water, dried
(MgSO4), and concentrated. The residue was purified by column
chromatography (SiO2, hexane-ethyl acetate ) 5:1) to afford 18j
as a yellow oil (81 mg, 27%) followed by an inseparable mixture
(2.5:1 ratio) of 2- and 3-cyclohexenones 20j as an oil (72 mg, 34%).
1
18j: IR (neat) 3057, 2360, 2340, 2049, 1976, 1716 cm-1; H
NMR (CDCl3) 7.84 (dd, J ) 3.0, 5.4 Hz, 2H), 7.72 (dd, J ) 3.0,
5.6 Hz, 2H), 5.43 (t, J ) 8.5 Hz, 1H), 3.76 (dd, J ) 6.0, 14.4 Hz,
1H), 3.26 (dd, J ) 9.6, 14.4 Hz, 1H), 2.75 (ddd, J ) 1.6, 6.1, 9.6
Hz, 1H), 2.14 (s, 3H), 1.83 (dd, J ) 3.8, 7.8, Hz, 1H), 1.69 (dd, J
) 3.7, 9.4 Hz, 1H); 13C NMR (CDCl3) 168.2, 134.2, 132.2, 123.5,
103.7, 91.8, 55.6, 37.2, 36.7, 25.3; FAB-HRMS m/z 368.0234 (calcd
for C17H14NO5Fe (M + H+) m/z 368.0221).
20j/20j′: IR (neat) 2969, 1772, 1709 cm-1. Anal. Calcd for
C15H13NO3·1/2H2O: C, 68.17; H, 5.34; N, 5.30. Found: C, 68.33;
H, 5.28; N, 5.07. 20j (2-cyclohexenone): 1H NMR (CDCl3) δ 7.77
(m, 2H), 7.67 (m, 2H), 6.92 (dd, J ) 10.1, 5.3 Hz, 1H), 6.10 (d, J
) 10.1 Hz, 1H), 4.90 (dt, J ) 12.8, 5.1 Hz, 1H), 3.80 (dd, J )
17.0, 12.8 Hz, 1H), 2.88-2.78 (m, 1H), 2.63 (dd, J ) 17.0, 4.8
Hz, 1H), 1.17 (d, J ) 7.4 Hz, 3H); 13C NMR (CDCl3) δ 197.4,
168.8, 153.0, 134.5, 131.9, 129.1, 123.7, 50.0, 37.5, 35.0, 14.3.
20j′ (3-cyclohexenone): 1H NMR (CDCl3, partial) δ 5.70 (br m,
1H), 5.06 (br t, J ) 6.5 Hz, 1H), 2.92 (m, 1H), 2.84 (m, 1H), 1.65
Acknowledgment. This work was supported by the National
Science Foundation (Grant CHE-0415771) and NIH and NSF
instrumentation grants (S10 RR019012 and CHE-0521323).
Some of the high-resolution mass spectra were provided by the
Washington University Mass Spectometry Resource, an NIH
Research Resource (Grant No. P41RR0954).
Supporting Information Available: Copies of the NMR
spectral data for 18b,g,j, 19d, 20f,g,i,j, 26, and 28 and CIF files
for the X-ray crystal structures for 12 and 18c. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM7006248