Studies on the Pauson-Khand reaction of alkynyl sulfoxides. Unexpectedly easy racemization of their dicobalt hexacarbonyl complexes

Article abstract of DOI:10.1016/S0957-4166(99)00032-4

The scope and limitations of the Pauson-Khand reactions of alkynyl sulfoxides with strained alkenes have been studied. (S)-1-Hexynyl p-tolyl sulfoxide and (S)-2-phenylethynyl p-tolyl sulfoxide afforded β-(p- tolylsulfinyl)enones in moderate yields and low

Full text of DOI:10.1016/S0957-4166(99)00032-4

Pergamon
Tetrahedron: Asymmetry 10 (1999) 457–471
Studies on the Pauson–Khand reaction of alkynyl sulfoxides.
Unexpectedly easy racemization of their dicobalt hexacarbonyl
complexes
Elvira Montenegro,a Albert Moyano,a Miquel A. Pericàs,a,∗ Antoni Riera,a,∗
Angel Alvarez-Larena b and Joan-F. Piniella b
aUnitat de Recerca en Síntesi Asimètrica, Departament de Química Orgànica, Universitat de Barcelona, c/ Martí i Franquès,
1-11, 08028 Barcelona, Spain
bUnitat de Cristal·lografia, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
Received 30 November 1998; accepted 26 January 1999
Abstract
The scope and limitations of the Pauson–Khand reactions of alkynyl sulfoxides with strained alkenes
have been studied. (S)-1-Hexynyl p-tolyl sulfoxide and (S)-2-phenylethynyl p-tolyl sulfoxide afforded β-(p-
tolylsulfinyl)enones in moderate yields and low diastereoselectivities. The diastereomeric mixtures were easily
separated by column chromatography and the sulfinyl group could be cleaved by a sequence involving reduction
to sulfide, carbonyl reduction and enol thioether hydrolysis to afford 1,3-rearranged enantiomerically enriched
α-butyl and α-phenyl enones. The absolute configuration of the Pauson–Khand adducts was determined by X-ray
diffraction. The decreased enantiomeric excess of the final products uncovered an unprecedented low temperature
racemization of the hexacarbonyl dicobalt complexes of alkynyl sulfoxides. © 1999 Elsevier Science Ltd. All
rights reserved.
1. Introduction
The cobalt mediated carbonylative co-cyclization of an alkyne and an alkene, known as the Pauson–
Khand reaction,1 is nowadays a well established methodology for the construction of five membered
rings. In the last decade, our group has been engaged in the development of enantioselective versions
of this useful reaction using the chiral auxiliary approach.2–6 Among these, we have developed several
methodologies in which a chiral inductor, covalently bonded to the alkyne participating in the process,
is able to control the diastereoselectivity in intermolecular Pauson–Khand reactions. Up to now, we
have explored for this purpose the use of ethynyl ethers I3 and 2-alkynoates II4 derived from chiral
∗
Correponding authors. E-mail: mpb@ursa.qo.ub.es and are@ursa.qo.ub.es
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00032-4

458
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
alcohols, ethynyl thioethers III5 derived from chiral thiols, and 2-alkynoyl amides IV6 derived from
chiral oxazolidones and sultams. For some of these systems, excellent levels of diastereoselectivity have
been achieved in spite of the fact that in all of these compounds the nearest stereogenic center in the
inductor is four or five bonds away from the newly created stereogenic center in the Pauson–Khand
adducts.
Unlike the above mentioned acetylenic derivatives, alkynyl sulfoxides 1 possess the stereogenic
center directly bonded to the acetylenic carbon. This property, combined with the easy availability of
enantiopure sulfoxides and the chemical versatility of sulfinyl compounds,7 made alkynyl sulfoxides
1 very attractive substrates for stereocontrolled Pauson–Khand reactions. We report herein our results
on the use of chiral enantiomerically pure alkynyl sulfoxides as steric controllers for intermolecular
Pauson–Khand reactions.
2. Results and discussion
2.1. Syntheses of the cobalt hexacarbonyl complexes of acetylenic sulfoxides
Enantiomerically pure alkynyl sulfoxides 1a–d covering a range of sterically and electronically
different substituents were selected for our study. Compounds 1a–c were prepared on a multigram scale
by a modification of the Andersen method,8 developed by Huda,9 whereas ethynylsulfoxide 1d (R=H)
was prepared by desilylation of 1a.9
The formation of the hexacarbonyl dicobalt complexes 2a–c took place uneventfully by stirring
1a–c with octacarbonyl dicobalt in toluene at room temperature. In the case of 1-hexynylsulfoxide 1b
the cobalt complex 2b was isolated in 82% yield although we decided, for practical reasons, not to
purify the cobalt complexes and to submit the crude solution to the Pauson–Khand reaction conditions.
Conversely, the formation of the cobalt complex of ethynyl sulfoxide 1d was problematic due to the easy
polymerization of the starting material in the presence of Co2(CO)8. Since our attempts to desilylate the
cobalt complex of 1a were unsuccessful, the polymerization of 1d was partially alleviated by preparing
the complex at low temperature (0°C).

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
459
2.2. Pauson–Khand reactions
The Pauson–Khand reaction of cobalt complexes 2a–d with strained alkenes 3g–e to afford the two
regioisomeric bicyclic enones 4 and 5 was studied next (Scheme 1 and Table 1).
Scheme 1.
The trimethylsilyl derivative 2a was completely reluctant to undergo the Pauson–Khand reaction,
probably due to the steric shielding provoked by the trimethylsilyl group, and no traces of cycloaddition
adducts were detected by TLC when a toluene solution of 2a was heated with norbornene for 36 h at
70°C (entry 1).
Sulfoxide 1d represents the opposite situation in steric shielding of the triple bond. When this sulfoxide
was converted into the corresponding dicobalt hexacarbonyl complex 2d (CH2Cl2, 0°C) and treated with
10 equiv. of norbornene and 6 equiv. of N-methylmorpholine N-oxide (NMO) at −78°C the α-sulfinyl
cyclopentenone 4de† was isolated from the crude reaction although only in 9% yield and almost without
any diastereoselectivity (Scheme 1, Table 1; entry 9).
Table 1
Intermolecular Pauson–Khand reactions of cobalt complexes 2a–d with alkenes 3e–g
†
In this article the polycyclic cyclopentenones are indicated by a number and a two letter code: the first letter refers to the R
group coming from the starting sulfoxide; the second describes the fragment arising from the alkene counterpart.

460
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
Figure 1.
To our satisfaction, the cyclization of complex 2b with norbornadiene (3f) proceeded cleanly under
thermal conditions affording a mixture of cyclopentenones in 69% overall yield (Table 1). The major
product of the reaction was the Pauson–Khand adduct 5bf, with the sulfoxide group placed β to the car-
bonyl. Thus, the presence of the n-butyl substituent provokes a reversal in the regiochemical preferences
of the reaction. Although the process took place with low diastereoselectivity, both diastereomers were
easily separable by column chromatography.
The regioisomeric adduct 4bf was not found in the crude product. Instead, the hydroxy cyclopentenone
6bf, which probably arises from this putative Pauson–Khand adduct, was isolated in a 23% yield. Fig. 1
shows the proposed relative ring stereochemistry of this adduct assuming an exo-attack to the olefin as is
usual in Pauson–Khand reactions.
A tentative mechanism to explain the presence of 6bf would involve an isomerization of the double
bond followed by a sulfoxide–sulfenate rearrangement (Scheme 2).10 However, other mechanisms such
as a rearrangement of a radical pair intermediate11 produced by homolytic cleavage of the carbon–sulfur
could also be considered.
Scheme 2.
The nowadays widely used N-oxide promoted conditions for this reaction12 were also tried. Unfor-
tunately, both the yield and the diastereomeric ratio of the Pauson–Khand adduct 5bf were lower than
under thermal activation, although they were both higher for the by-product 6bf (entry 3).
Using norbornene as a reacting olefin, the yield of the Pauson–Khand adduct 5be was lower than
using norbornadiene under both thermal and N-oxide reaction conditions (entries 4 and 5). In this case,
neither the regioisomeric Pauson–Khand adduct 4be nor the by-product arising from its decomposition
6be could be isolated from the crude. On the other hand, the use of a more strained alkene such as
bicyclo[3.2.0]hept-6-ene 3g gave, under thermal conditions, a higher overall yield of cyclopentenones
(entry 6). A nearly 1:1 mixture of the Pauson–Khand adduct 5bg and the tricyclic alcohol 6bg (Fig. 1)
was obtained, the diastereomeric excess of 5bg being in any case modest (2:1 dr).
The Pauson–Khand reaction using the cobalt complex 2c prepared from 2-phenylethynyl p-tolyl
sulfoxide was studied next (entries 7 and 8). Once again, only the thermal conditions afforded good
yields of the cycloadduct 5ce. Due to the higher steric hindrance of the phenyl group relative to n-butyl
the reaction was completely regioselective and, consequently, the yield of the Pauson–Khand adduct 5ce
increased. Moreover, the selectivity increased up to a 2.6:1 mixture of easily separable diastereomers.

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
461
Figure 2.
2.3. Absolute configuration of the major diastereomers
The diastereomeric mixtures of the Pauson–Khand adducts 5be–bf and 5ce could be separated by
column chromatography, affording diastereomerically pure β-sulfinylenones. The removal of the sulfo-
xide group from these enones would afford enantiomerically pure cyclopentenones if no racemization
took place along the process. Since these products were highly crystalline it was possible to perform X-
ray diffraction analyses. The minor diastereomer of 5be crystallized nicely from hexane–ether. The X-ray
diffraction of these crystals confirmed the assigned structure and revealed the stereochemical relationship
between the sulfoxide and the other stereogenic centers in the molecule.
Thus, taking into account the known absolute configuration of the starting acetylenic sulfoxide, the
stereochemistry of the diastereomers of the Pauson–Khand adduct 5be must be the one depicted in Fig. 2.
In order to remove the chiral auxiliary from these adducts, a reductive treatment with Raney-
Ni was performed: the major diastereomers of β-sulfinylenones 5be and 5bf afforded on reductive
desulfinylation the same bicyclic enone (+)-7be13 due to the simultaneous reduction of the double bond
in 5bf. In this way the stereochemistry of 5bf could also be firmly established, as well as the relationship
between the sign of the optical rotation and the absolute configuration of enone 7be (Scheme 3).
Scheme 3.
The concomitant reduction of the double bond during the cleavage of the sulfoxide led us to look
for more selective, alternative protocols. Whereas the reductive elimination of sulfinyl groups α to a
carbonyl is well documented,7c the references concerning cleavage of a sulfoxide β to an enone are
scarce.14 In our hands, reductive treatments involving the use of sodium15 or aluminium16 amalgams or of
samarium iodide17 led to complex mixtures where the corresponding sulfide was the major product. After
some experimentation we found that the following reaction sequence afforded the corresponding 1,3-

462
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
rearranged enones in good yields: (a) sulfoxide reduction to sulfide; (b) carbonyl reduction by DIBALH;
and (c) enol thioether hydrolysis with concomitant dehydration of one of the so formed β-hydroxy
carbonyl system. Thus, starting from the major diastereomer 5bf, sulfide (+)-8bf could be prepared
in 70% yield by reduction with sodium iodide and trifluoroacetic anhydride.18 This sulfide was then
submited to DIBALH reduction and hydrolysis in the presence of mercuric salts19 to afford enone (−)-
7bf in 63% yield (Scheme 4). In so doing, the absolute configuration of this enone, already known in
racemic form,20,21 was unambiguously established.
Scheme 4.
On the other hand, from a hexane–ether solution of the major diastereomer of 5ce a few crystals sui-
table for X-ray diffraction were collected. The crystalline cell showed the presence of both enantiomers,
thus indicating that the crystals corresponded to a racemate. However, the relative configuration between
the sulfoxide and the bicyclic system could be determined and the absolute configuration of the major
adduct was assigned assuming that the sulfur atom had the same configuration as in the starting sulfoxide
(Fig. 3).
The optimized protocol for the removal of the sulfoxide group was also applied to the major adduct 5ce
leading to the enantiomerically enriched bicyclic enone (+)-7ce with a similar overall yield (Scheme 5).
Enone 7ce, prepared by Pauson–Khand reaction of phenylacetylene and norbornene, has served as an
example in many methodological studies of the reaction21,22 including the seminal work of Pauson et al.23
Moreover, it has been prepared in enantiomerically pure form by asymmetric Pauson–Khand reactions24
although its absolute stereochemistry could not be determined. Now, the relationship between the sign of
its rotatory power and configuration has been established for the first time.
Figure 3.
Scheme 5.

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
463
The same sequence of reactions was also applied to the minor diastereomers of 5bf and 5ce and leading
to the enantiomeric enones (+)-7bf and (−)-7ce, respectively.
2.4. Enantiomeric excess of the adducts
The optical purity of enones 7bf and 7ce was analyzed by GC using a Cyclodex-β column. As
suspected after the X-ray analysis of the adduct 5ce, these compounds were not enantiomerically pure.
The enantiomeric excess of (−)-7bf was 71% and only 25% ee in the case of (+)-7ce, clearly indicating
that a racemization process had occurred along the sequences.
The enantiomeric excess of 7be, obtained by direct desulfurization with Raney-Ni, was also measured
and turned out to be 75% ee. The observation of partial racemization irrespective of the desulfinylation
conditions employed tends to indicate that the racemization did not take place during the removal of the
sulfoxide through a symmetrical intermediate, but at the cobalt carbonyl complex stage or during the
Pauson–Khand reaction. A polarimetric study of the enantiomeric excess of the cobalt carbonyl complex
5b showed that this compound is configurationally unstable and racemizes at an appreciable rate even at
room temperature. A linear relationship (R2=0.971) between ln c and t indicated that the racemization
follows a first order kinetics and, therefore, the mechanism should consist of a single unimolecular step.
The measured rate constant at 25°C was 2.8 10−6 s−1. This means that starting from an enantiomerically
pure toluene solution of 5b, after 7 h at room temperature, the enantiomeric excess would be only 86%
ee.
This unexpected low temperature racemization is completely unprecedented for a non-allylic sul-
foxide. It is worth recalling that the racemization by pyramidal inversion in alkyl or aryl sulfoxides
takes place at a measurable rates only at temperatures higher than 200°C25 and in benzylic sulfoxides at
135–155°C.26 According to the literature precedents, we have envisaged three possible mechanisms for
the racemization of the dicobalt hexacarbonyl complexes of alkynyl sulfoxides: (a) homolytic cleavage of
the sulfur–carbon bond; (b) pyramidal inversion; and (c) formation of a pentavalent sulfur intermediate
followed by Berry pseudorotations. These tentative mechanisms are currently being studied in our
laboratories both from the experimental and theoretical point of view. The results of this study will be
reported in due course.
In summary, the elaboration of the adducts arising from the Pauson–Khand reaction of alkynyl
sulfoxides with strained alkenes has allowed the establishment of the absolute configuration of some
synthetically important polycyclic ketones. Moreover, the observed loss of enantiomeric excess in
diastereomerically pure Pauson–Khand adducts arising from enantiomerically pure sulfoxides, has been
traced to the unprecedented, extremely easy racemization of the dicobalt hexacarbonyl complexes of
alkynyl sulfoxides.
3. Experimental
3.1. General
Melting points were determined in an open capillary tube and are uncorrected. Optical rotations were
measured at room temperature (23°C) on a Perkin–Elmer 241 MC polarimeter (concentration in g/100
mL). Infrared spectra were recorded on a Perkin–Elmer 681, or on a Nicolet 510 FTIR using an NaCl
1
film technique. H NMR were recorded at 200 or 500 MHz (s=singlet, d=doublet, t=triplet, q=quartet,
dt=double triplet, m=multiplet and b=broad). 13C NMR were recorded at 50.3 MHz or 125.7 MHz.

464
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
Carbon multiplicities have been assigned by DEPT experiments. In all cases, chemical shifts are in
1
ppm downfield of TMS (referenced to an internal standard for H NMR, and to the central signal of
CDCl3 for 13C NMR). Diastereomeric ratios were determined by 13C NMR. Mass spectra were recorded
on a Hewlett–Packard 5890 instrument at 70 eV ionizing voltage; ammonia was used for chemical
ionization (CI). THF and diethyl ether were distilled from sodium benzophenone ketyl. All reactions
were performed in oven-dried glassware under an N2 atmosphere. Reaction progress was monitored by
TLC (Merck DC-Alufolien Kieselgel 60 F254) eluting with hexanes/ethyl acetate mixtures.
Alkynyl sulfoxides 1a–d were prepared according to the procedures described in the literature.9
The optical purity of 1b and 1c was checked by polarimetry. (+)-(S)-1-Hexynyl p-tolyl sulfoxide 1b:
[α]D23=+80.3 (c 1.3 CHCl3); lit.9 [α]D23=+77.6 (c 1.2 CHCl3). (+)-(S)-2-Phenylethynyl p-tolyl sulfoxide
1c: [α]D23=+83.7 (c 1.2 CHCl3); lit.27 [α]D23=+76 (c 2.5 CHCl3).
3.2. Thermal Pauson–Khand reaction
3.2.1. General procedure A
To a solution of acetylenic sulfoxide (0.45 mmol) in toluene (10 mL), Co2(CO)8 (0.48 mmol) was
added. The formation of a dark red colored complex was observed and monitored by TLC. After 30
minutes of stirring at room temperature, a solution of the alkene (4.5 mmol) in toluene (5 mL) was added
and the reaction mixture was heated at the specified temperature until no dicobalt hexacarbonyl complex
could be observed by TLC. The solid suspension was filtered through Celite, and washed thoroughly with
CH2Cl2. The combined organic extracts were evaporated under vacuum. The crude product was purified
by column chromatography on Et3N pre-treated silica gel (2.5% v/v) eluting with diethyl ether/hexane
mixtures of increasing polarity to yield the corresponding cyclopentenone.
3.3. Amine N-oxide promoted Pauson–Khand reaction
3.3.1. General procedure B
To a solution of acetylenic sulfoxide (0.09 mmol) in CH2Cl2 (25 mL), Co2(CO)8 (0.1 mmol) was
added. The formation of a dark red colored complex was observed and monitored by TLC. After 30
minutes of stirring at room temperature, the corresponding alkene was added (0.9 mmol) and the reaction
mixture was cooled at −78°C. Then, solid amine N-oxide (6–10 equivalents) was added and the reaction
was stirred at the specified temperature. The solid suspension was filtered through Celite and washed
thoroughly with CH2Cl2. The combined organic extracts were evaporated under vacuum. The crude
product was purified by column chromatography on Et3N pre-treated silica gel (2.5% v/v) eluting with
diethyl ether/hexane mixtures of increasing polarity to yield the corresponding cyclopentenone.
3.4. Pauson–Khand reactions of (+)-(S)-1-hexynyl p-tolyl sulfoxide (1b) with norbornadiene
The general procedure A (65°C for 27 h) using as reagents 1b (200 mg, 0.9 mmol), toluene (30 mL),
Co2(CO)8 (362 mg, 0.95 mmol) and norbornadiene (828 mg, 9 mmol), afforded 130 mg of 5bf (46%
yield) as a mixture of two diastereomers, separable by chromatography (1.6:1 dr) and 45 mg of 6bf (23%
yield) as a mixture of diastereomers (2.9:1 dr).
The general procedure B using as reagents 1b (100 mg, 0.45 mmol), CH2Cl2 (22 mL), Co2(CO)8
(163 mg, 0.48 mmol), norbornadiene (414 mg, 4.5 mmol) and NMO·H2O (605 mg, 4.5 mmol) (added
portionwise at 0°C) afforded 23 mg (15%) of 5bf and 30 mg of 6bf (31%, 4.6:1 dr).

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
465
3.4.1. (1S,2S,6R,7R)-4-Butyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one (5bf-major)
[α]D23=−11.7 (c 1.4 CHCl3). IR (film) ν=2960, 2880, 1710, 1600, 1085, 1050, 810, 620 cm−1. H
1
NMR (200 MHz, CDCl3) δ=7.56, 7.35 (AB, J=8.3 Hz, 4H), 6.13 (s, 2H), 3.05 (d, J=7.7 Hz, 1H), 2.91 (s,
1H), 2.6–2.3 (m, 2H), 2.4 (s, 3H), 1.5–1.2 (m, 8H), 0.93 (t, J=6.9 Hz, 3H). 13C NMR (75.4 MHz, CDCl3)
δ=206.3 (C), 170.6 (C), 151.3 (C), 141.7 (C), 138.6 (C), 137.8 (CH), 136.9 (CH), 130.02 (CH), 124.5
(CH), 53.4 (CH), 45.3 (CH), 43.8 (CH), 42.5 (CH), 41.1 (CH2), 30.5 (CH2), 23.6 (CH2), 22.7 (CH2),
21.2 (CH3), 13.6 (CH3). MS (DIP-CI-NH3) m/e=358 (M++18, 100%), 340 (M+, 1%), 252 (M+−88, 3%),
236 (M+−104, 5%). Conditions for HPLC analysis: Nucleosil C18 (25 cm) column, 60% CH3CN, 0.7
mL/min, λ=254 nm, tR (min)=22.43.
3.4.2. (1R,2R,6S,7S)-4-Butyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one (5bf-minor)
[α]D23=−12.4 (c 1.0 CHCl3). IR (film) ν=2960, 2880, 1710, 1600, 1500, 1085, 1050, 810 cm−1. H
1
NMR (200 MHz, CDCl3) δ=7.55, 7.35 (AB, J=8.1 Hz, 4H), 6.3–6.1 (m, 2H), 3.42 (s, 1H), 2.92 (s, 1H),
2.43 (s, 3H), 2.68, 2.25 (AB, J=7.7 Hz, 2H), 1.45–1.26 (m, 8H), 0.94 (t, J=6.5 Hz, 3H). 13C NMR (75.4
MHz, CDCl3) δ=207.3 (C), 171 (C), 150.1 (C), 140.2 (C), 138.8 (CH), 136.6 (CH), 130.1 (CH), 124.3
(CH), 53.4 (CH), 45.3 (CH), 43.8 (CH), 42.5 (CH), 41.1 CH2). 30.5 (CH2), 23.6 (CH2), 22.7 (CH2), 21.2
(CH3), 13.6 (CH3). MS (DIP-CI-NH3) m/e=358 (M++18, 33%), 341 (M++1, 2%), 236 (M+−104, 100%).
Conditions for HPLC analysis: Nucleosil C18 (25 cm) column, 60% CH3CN, 0.7 mL/min, λ=254 nm, tR
(min)=23.30.
3.4.3. 5-(1-Hydroxybutyl)tricyclo[5.2.1.02,6]deca-4,8-dien-3-one (6bf)
1
IR (film) ν=3450 (b), 2970, 2880, 1775, 1700, 1610, 730, 715 cm−1. H NMR (200 MHz, CDCl3)
δ=6.24 (s, 1H), 4.55 (m, 1H), 2.94 (s, 1H), 2.78 (m, 1H), 2.38 (d, J=5 Hz, 1H), 2.09 (a, 1H), 1.75–1.3 (m,
9H), 0.98 (t, J=7 Hz, 3H). 13C NMR (50 MHz, CDCl3) δ=209.1 (C), 184.9 (C), 138.2 (CH, minor), 137.8
(CH), 137.6 (CH), 137.3 (CH, minor), 132.9 (CH, minor), 132.1 (CH), 70.6 (CH), 70.5 (CH, minor), 53.6
(CH), 49.6 (CH), 43.4 (CH, minor), 43.2 (CH), 42.9 (CH, minor), 42.4 (CH), 41.4 (CH2), 41.1 (CH2,
minor), 37.9 (CH2), 18.6 (CH2, minor), 18.4 (CH2), 13.8 (CH3). MS (DIP-EI) m/e=218 (M+, 5%), 175
(M+−43, 22%), 146 (M+−72, 43%), 117 (M+−101, 57%), 91 (M+−127, 100%).
3.5. Pauson–Khand reactions of 1-hexynyl p-tolyl (+)-(S)-sulfoxide (1b) with norbornene
The general procedure A (65°C for 27 h) using as reagents 1b (100 mg, 0.45 mmol), toluene (15 mL),
Co2(CO)8 (163 mg, 0.48 mmol) and norbornene (423 mg, 4.5 mmol) afforded 52 mg of 5be as a mixture
of two diastereomers separable by chromatography (34%, 1.8:1 dr).
The general procedure B using as reagents 1b (200 mg, 0.91 mmol), CH2Cl2, of Co2(CO)8 (342 mg,
0.1 mmol), norbornene (428 mg, 4.5 mmol) and NMO (640 mg, 0.54 mmol) afforded 14 mg (4%) of
5be.
3.5.1. (1R,2S,6R,7S)-4-Butyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.02,6 ]dec-4-en-3-one (5be-major)
[α]D23=+29.4 (c 1.1 acetone). IR (film) ν=2950, 2870, 1705, 1085, 1050, 810 cm−1. H NMR (500
1
MHz, CDCl3) δ=7.54, 7.34 (AB, J=8.5 Hz, 4H), 2.86, 2.23 (AB, J=6 Hz, 2H), 2.61–2.46 (m, 2H), 2.43
(s, 3H), 2.4 (s, 1H), 1.93 (s, 1H), 1.56–1.19 (m, 8H), 0.93 (t, J=7 Hz, 3H), 0.81–0.79 (m, 2H). 13C NMR
(125.7 MHz, CDCl3) δ=207.9 (C), 170.7 (C), 150.4 (C), 141.9 (C), 138.9 (C), 124.7 (CH), 130.1 (CH),
54.5 (CH), 46.2 (CH), 39.4 (CH), 37.8 (CH), 31.2 (CH2), 30.6 (CH2), 28.5 (CH2), 28.2 (CH2), 23.4
(CH2), 22.8 (CH2), 21.3 (CH3), 13.7 (CH3). MS (DIP-EI) m/e=342 (M+, 2%), 325 (M+−17, 100%), 283
(M+−59, 21%), 203 (M+−139, 2%).

466
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
3.5.2. (1S,2R,6S,7R)-4-Butyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.0 2,6]dec-4-en-3-one (5be-minor)
[α]D23=−24.5 (c 1.71 acetone). IR (film) ν=2980, 2890, 1725, 1095, 1060, 820 cm−1. 1H NMR (500
MHz, CDCl3) δ=7.54, 7.35 (AB, J=8 Hz, 4H), 2.92 (d, J=4 Hz, 1H), 2.57, 2.12 (AB, J=5.5 Hz, 2H),
2.47–2.45 (m, 2H), 2.43 (s, 3H), 2.41 (d, J=4 Hz, 1H), 1.63–1.11 (m, 10H), 0.94 (t, J=7 Hz, 3H). 13C
NMR (50 MHz, CDCl3) δ=208.8 (C), 170.4 (C), 150.2 (C), 142.06, (C) 138.9 (C), 130.3 (CH), 124.6
(CH), 54.7 (CH), 46.6 (CH), 39.15 (CH), 39.3 (CH), 31.6 (CH2), 30.6 (CH2), 28.9 (CH2), 28.2 (CH2),
23.8 (CH2), 22.9 (CH2), 21.5 (CH3), 13.8 (CH3). MS (DIP-EI) m/e=342 (M+, 12%), 325 (M+−17, 100%),
283 (M+−59, 25%), 251 (M+−91, 1%), 139 (M+−203, 13%).
3.6. Pauson–Khand reaction of (+)-(S)-1-hexynyl p-tolyl sulfoxide (1b) with bicyclo[3.2.0]hept-6-ene
The general procedure A (65°C for 12 h) using as reagents 1b (200 mg, 0.9 mmol), toluene (20 mL),
Co2(CO)8 (362 mg, 0.95 mmol) and bicyclo[3.2.0]hept-6-ene (846 mg, 9 mmol) in toluene (10 mL)
afforded 110 mg (32%, 2:1 dr) of 4-butyl-5-[(S)-p-tolylsulfinyl]tricyclo[5.3.0.02,6]dec-4-en-3-one 5bg
and 65 mg (33%) of 5-(1-hydroxybutyl)tricyclo[5.3.0.02,6 ]dec-4-en-3-one 6bg (1.2:1 dr).
3.6.1. 4-Butyl-5-[(S)-p-tolylsulfinyl]tricyclo[5.3.0.02,6 ]dec-4-en-3-one (5bg)
1
IR (film) ν=2960, 2880, 1710, 1600, 1500, 1090, 1050, 815 cm−1. H NMR (200 MHz, CDCl3)
δ=7.35, 7.59 (AB, J=8 Hz, 4H), 3.05 (m, 1H), 2.7–0.95 (m, 18H), 2.42 (s, 3H). 13C NMR (50 MHz,
CDCl3) δ=208.9 (C), 208.8 (C, minor), 172.5 (C, minor), 171.9 (C), 148.6 (C), 147.6 (C, minor), 142
(C), 137.9 (C), 130.1 (CH, minor), 130.0 (CH), 124.6 (CH, minor), 124.4 (CH), 49.1 (CH), 48.9 (CH,
minor), 45.3 (CH), 40.6 (CH, minor), 39.6 (CH, minor), 39.4 (CH), 38.5 (CH), 32.9 (CH2, minor), 32.8
(CH2), 32.1 (CH2), 30.8 (CH2), 30.3 (CH2, minor), 24.5 (CH2, minor), 24.3 (CH2), 23.7 (CH2), 22.7
(CH2), 21.4 (CH3), 13.8 (CH3). MS (DIP-CI-NH3) m/e=360 (M++18, 6%), 342 (M+, 2%), 238 (M+−105,
100%), 222 (M+−120, 17%).
3.6.2. 5-(1-Hydroxybutyl)tricyclo[5.3.0.02,6]dec-4-en-3-one (6bg)
1
IR (film) ν=3400 (b), 2950, 2860, 1680, 1605 cm−1. H NMR (200 MHz, CDCl3) δ=6.28 (major),
6.18 (minor) (s, 1H), 4.56 (m, 1H), 2.95–1.4 (m, 15H), 0.96 (t, J=7 Hz, 3H). 13C NMR (50 MHz,
CDCl3) δ=211.9 (C, minor), 211.8 (C), 186.5 (C), 185.9 (C, minor), 129.3 (CH, minor), 129.2 (CH),
70.9 (CH, minor), 69.9 (CH), 49.2 (CH), 49.0 (CH, minor), 44.6 (CH, minor), 44.5 (CH), 44.4 (CH),
43.9 (CH, minor), 40.0 (CH), 38.9 (CH, minor), 37.9 (CH2), 37.6 (CH2, minor), 32.8 (CH2), 32.5 (CH2),
32.4 (CH2, minor), 24.7 (CH2), 24.6 (CH2, minor), 18.5 (CH2, minor), 18.4 (CH2), 13.9 (CH3), 13.7
(CH3, minor). MS (DIP-CI-NH3) m/e=458 (2M++18, 20%), 441 (2M++1, 100%), 238 (M++18, 73%),
221(M++1, 11%).
3.7. Pauson–Khand reaction of (+)-(S)-2-phenylethynyl p-tolyl sulfoxide (1c) with norbornene
The general procedure A (2 h at room temperature, 2 h at 50°C, 12 h at 70°C and 7 h at 100°C) using
as reagents 1c (200 mg, 0.83 mmol), toluene (20 mL), Co2(CO)8 (310 mg, 0.92 mmol) and norbornene
(781 mg, 8.3 mmol) afforded 160 mg of 5ce (53%, 2.6:1 dr).
The general procedure B using as reagents 1c (100 mg, 0.42 mmol), CH2Cl2 (10 mL), Co2(CO)8 (150
mg, 0.44 mmol), norbornene (395 mg, 4.2 mmol) and TMANO (189 mg, 2.52 mmol) gave 15 mg (10%)
of 5ce (1:1 dr).

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
467
3.7.1. (1S,2R,6S,7R)-4-Phenyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.02,6 ]dec-4-en-3-one (5ce-major)
[α]D23=−28.9 (c 1.3 CHCl3). IR (film) ν=2970, 2890, 1720, 1090, 1060, 700 cm−1. H NMR (200
MHz, CDCl3) δ=7.43–7.25 (m, 9H), 3.05 (s, 1H), 2.78, 2.3 (AB, J=5 Hz, 2H), 2.49 (s, 1H), 2.38 (s, 3H),
1.35–1.1 (m, 6H). 13C NMR (50 MHz, CDCl3) δ=206.7 (C), 175.0 (C), 148.0 (C), 142.9 (C), 139.9 (C),
130.02 (CH), 129.3 (CH), 128.6 (CH), 124.2 (CH), 55.2 (CH), 46.2 (CH), 39.6 (CH), 39.5 (CH), 31.7
(CH2), 29.1 (CH2), 28.2 (CH2), 21.4 (CH3). MS (DIP-EI) m/e=363 (M++1, 10%), 362 (M+, 40%), 314
(M+−48, 31%), 299 (M+−63, 14%), 255 (M+−107, 26%).
1
3.7.2. (1R,2S,6R,7S)-4-Phenyl-5-[(S)-4-tolylsulfinyl]tricyclo[5.2.1.02,6 ]dec-4-en-3-one (5ce-minor)
1
[α]D23=−20.9 (c 1.1 CHCl3). IR (film) ν=2980, 2900, 1720, 1090, 1060, 840, 710 cm−1. H NMR
(200 MHz, CDCl3,) δ=7.45–7.15 (m, 9H), 3.34, 2.47 (AB, J=5.8 Hz, 2H), 2.51 (s, 1H), 2.36 (s, 3H),
2.1 (s, 1H), 1.57–1.25 (m, 6H). 13C NMR (50 MHz, CDCl3) δ=175.2 (C), 148.1 (C), 142.0 (C), 139.5
(C), 129.9 (CH), 129.2 (CH), 128.7 (CH), 124.2 (CH), 54.9 (CH), 46.3 (CH), 40.2 (CH), 38.1 (CH), 31.3
(CH2), 28.7 (CH2), 28.3 (CH2), 21.3 (CH3). MS (DIP-EI) m/e=363 (M++1, 10%), 362 (M+, 40%), 314
(M+−48, 31%), 299 (M+−63, 15%), 255 (M+−107, 27%).
3.8. (1R,2S,6S,7S)-4-Butyltricyclo[5.2.1.0 2,6]dec-4-en-3-one [(+)-7be]
(a) To a solution of the adduct 5be-major (100 mg, 0.3 mmol), in ethanol (10 mL) was added Raney-
Ni (50% suspension in water, 1.2 mmol) in ethanol (5 mL). The reaction mixture was stirred at room
temperature until no starting material was observed by TLC. The suspension was filtered through Celite,
washed thoroughly with CH2Cl2 and the solvent was removed under reduced pressure. The crude product
was purified by column chromatography on Et3N pre-treated silica gel (2.5% v/v) eluting with diethyl
ether/hexane mixtures of increasing polarity to yield 50 mg of (+)-7be as an oil (85% yield, 54% ee
by GC). [α]D23=+90.1 (c 1.4 CHCl3). (b) The same procedure using as reagents 5bf-major (90 mg 0.3
mmol), ethanol (10 mL) and Raney-Ni (1.2 mmol), afforded 31 mg of (+)-7be as an oil (56% yield, 75%
ee by GC). [α]D23=+108.3 (c 1.5 CHCl3). Conditions for chiral GC analysis: Cyclodex-β (50 m, 0.25
mm ID) column, 150°C, tR (min)=83.0 (minor), 85.2 (major). IR (film) ν=2950, 2870, 1700, 1630, 1450,
1185, 1050 cm−1. 1H NMR (200 MHz, CDCl3) δ=7.16 (m, 1H), 2.55 (s, 1H), 2.35 (s, 1H), 2,16 (m, 2H),
1.6–1.27 (m, 12H), 0.94 (t, J=7 Hz, 3H). 13C NMR (50 MHz, CDCl3) δ=211.2 (C), 158.6 (CH), 149.3
(C), 53.8 (CH), 48.1 (CH), 38.9 (CH), 37.9 (CH), 30.9 (CH2), 29.9 (CH2), 28.9 (CH2), 28.4 (CH2), 24.3
(CH2), 23.4 (CH2), 13.8 (CH3). MS (DIP-CI-NH3) m/e=222 (M++18, 100%), 205 (M++1, 45%).
3.9. (1S,2R,6R,7R)-4-Butyltricyclo[5.2.1.02,6 ]dec-4-en-3-one [(−)-7be]
The procedure described for (+)-7be using as a reagents 5be-minor (58 mg, 0.17 mmol), ethanol (6
mL) and Raney-Ni (6.3 mmol), afforded 19 mg of (−)-7be (56%, 54% ee by GC) as an oil. [α]D23=−72.7
(c 1.0 CHCl3). Conditions for chiral GC analysis: Cyclodex-β (50 m, 0.25 mm ID) column, 150°C, tR
(min)=82.5 (major), 84.9 (minor). Spectroscopic data identical to those of (+)-7be.
3.10. (1S,2S,6R,7R)-4-Butyl-5-p-tolylsulfanyltricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one [(+)-8bf]
To a cold (−40°C) suspension of 5bf-major (73 mg, 0.22 mmol) and NaI (0.70 mmol) in acetone (6.5
mL) was added trifluoroacetic anhydride (1.1 mmol). The reaction mixture was stirred at this temperature
until no starting material was observed. The reaction was quenched with sat. Na2SO3 and NaHCO3. The
acetone was removed under vacuum and the aqueous phase was extracted with diethyl ether. The organic

468
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
phase was dried over MgSO4 and the solvent was removed under reduced pressure. The crude product
was purified by column chromatography on Et3N pre-treated silica gel (2.5% v/v) eluting with diethyl
ether/hexane mixtures of increasing polarity to yield 50 mg of (+)-8bf (70%). [α]D23=+209.1 (c 0.1
1
CHCl3). IR (film) ν=2950, 2870, 1690, 1590, 1490, 810 cm−1. H NMR (200 MHz, CDCl3) δ=7.43,
7.19 (AB, J=8.3 Hz, 4H), 6.06, 5.81 (ABXY, J=5.64 Hz, J0=3 Hz, 2H), 3.89 (s, 1H), 2.61 (d, J=5 Hz,
1H), 2.46 (s, 1H), 2.37 (s, 3H), 2.3–2.15 (m, 3H), 1.5–1.3 (m, 6H), 0.90 (t, J=6.9 Hz, 3H). 13C NMR
(50 MHz, CDCl3) δ=204.9 (C), 171.4 (C), 142.9 (C), 139.7 (C), 137.5 (CH), 137.3 (CH), 134.9 (CH),
130.04 (CH), 52.8 (CH), 49.7 (CH), 43.8 (CH), 43.1 (CH), 41.1 (CH2), 29.7 (CH2), 23.8 (CH2), 22.8
(CH2), 21.2 (CH3), 13.9 (CH3). MS (DIP-CI-NH3) m/e=342 (M++18, 56%), 325 (M++1, 100%).
3.11. (1R,2R,6S,7S)-4-Butyl-5-p-tolylsulfanyltricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one [(−)-8bf]
The procedure described for (+)-8bf starting from 5bf-minor (50 mg, 0.14 mmol), afforded 15 mg of
(−)-8bf (33%). [α]D23=−199.1 (c 0.9 CHCl3). Spectroscopic data identical to those of (+)-8bf.
3.12. (1S,2R,6S,7R)-4-Phenyl-5-p-tolylsulfanyltricyclo[5.2.1.02,6 ]dec-4-en-3-one [(−)-8ce]
The procedure described for (+)-8bf (3 h, −20°C) starting from 5ce-major (81 mg, 0.23 mmol) gave
36 mg (45%) of (−)-8ce. [α]D23=−82.1 (c 1.9 CHCl3). IR (film) ν=2940, 2850, 1675, 1550, 1480, 1290,
800, 740, 690 cm−1. 1H NMR (200 MHz, CDCl3) δ=7.51–7.18 (m, 9H), 2.35, 2.65 (AB, J=5.7 Hz, 2H),
2.45 (s, 1H), 2.39 (s, 3H), 2.15 (s, 1H), 1.55–0.80 (m, 6H) ppm. 13C NMR (50 MHz, CDCl3) δ=204.4
(C), 173.5 (C), 140 (C), 135.1 (CH), 130.0 (CH), 128.9 (CH), 128.1 (CH), 127.9 (CH), 54.8 (CH), 50.04
(CH), 39.6 (CH), 39.2 (CH), 31.2 (CH2), 28.8 (CH2), 28.2 (CH2), 21.3 (CH3) ppm. MS (DIP-CI-NH3)
m/e=364 (M++18, 100%), 347 (M++1, 82%).
3.13. (1R,2S,6R,7S)-4-Phenyl-5-p-tolylsulfanyltricyclo[5.2.1.02,6 ]dec-4-en-3-one [(+)-8ce]
The procedure described for (+)-8bf (30 min, −40°C) starting from 5ce-minor (95 mg, 0.26 mmol)
gave 50 mg (55%) of (+)-8ce. [α]D23=+34.5 (c 1.1 CHCl3). Spectroscopic data identical to those of
(−)-8ce.
3.14. (1R,2R,6R,7S)-4-Butyltricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one [(−)-7bf]
To a cold (−60°C) solution of the sulfide (+)-8bf (50 mg, 0.15 mmol) in diethyl ether, DIBALH (1.2
mmol, 1 M in hexanes) was added. The reaction was stirred at this temperature until no starting material
was observed by TLC. The reaction was quenched by dropwise addition of MeOH and the organic
phase was washed with saturated aqueous NaHCO3. The aqueous phase was extracted with CH2Cl2. The
combined organic extracts were dried over Na2SO4 and the solvent was removed under vacuum. To the
crude (45 mg of alcohol) dissolved in MeOH (6 mL), were added two drops of aqueous 35% HCl, HgCl2
(84 mg, 0.31 mmol) and HgO (32 mg, 0.15 mmol). The reaction was stirred at room temperature until
no starting material was observed by TLC (24 h). The solid suspension was filtered through Celite, and
washed thoroughly with diethyl ether. The combined organic extracts were evaporated under vacuum.
The crude product was purified by column chromatography on Et3N pre-treated silica gel (2.5% v/v)
eluting with diethyl ether/hexane mixtures of increasing polarity to afford 15 mg (63%, 71% ee by GC)
of (−)-7bf. [α]D23=−58.4 (c 0.63 CHCl3). Conditions for chiral GC analysis: Cyclodex-β (50 m, 0.25
mm ID) column, 160°C, tR (min)=47.05 (major), 47.9 (minor). IR (film) ν=3090, 2980, 2940, 2890,

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
469
1705, 1470, 1330, 1220, 1150, 860 cm−1. 1H NMR (200 MHz, CDCl3) δ=7.16 (m, 1H), 6.17–6.31 (m,
2H), 2.90 (s, 1H), 2.69 (m, 2H), 2.28 (d, J=5 Hz, 1H), 2.16 (t, J=7 Hz, 2H, 1.15–1.55 (m, 6H), 0.90
(t, J=7 Hz, 3H). 13C NMR (50 MHz, CDCl3) δ=158.7 (CH), 150.9 (C), 138.3 (CH), 137.0 (CH), 52.5
(CH), 47.6 (CH), 43.6 (CH), 42.9 (CH), 41.2 (CH2), 29.9 (CH2), 24.6 (CH2), 22.5 (CH2), 13.8 (CH3).
MS (DIP-CI-NH3) m/e=237 (M++35, 56%), 220 (M++18, 100%), 203 (M++1, 9%).
3.15. (1S,2S,6S,7R)-4-Butyltricyclo[5.2.1.02,6 ]deca-4,8-dien-3-one [(+)-7bf]
The procedure described for (−)-7bf starting from (−)-8bf (15 mg, 0.05 mmol) afforded 7 mg (87%,
71% ee by GC) of (+)-7bf. Conditions for chiral GC analysis: Cyclodex-β (50 m, 0.25 mm ID) column,
160°C, tR (min)=47.2 (minor), 48.02 (major). Spectroscopic data identical to those of (−)-7bf.
3.16. (1R,2S,6S,7S)-4-Phenyltricyclo[5.2.1.02,6]dec-4-en-3-one [(+)-7ce]
The procedure described for (−)-7bf starting from (−)-8ce (34 mg, 0.1 mmol) after 24 h afforded 16 mg
(89%, 25% ee) of (+)-7ce. [α]D23=+15.6 (c 1.1 benzene). Conditions for chiral GC analysis: Cyclodex-β
(50 m, 0.25 mm ID) column, 150°C, tR (min)=51.8 (minor), 53.7 (major). IR (film) ν=3020, 2940, 2860,
1690, 1480, 750 cm−1. 1H NMR (200 MHz, CDCl3) δ=7.72–7.64 (m, 3H), 7.38–7.26 (m, 3H), 2.71 (m,
1H), 2.5 (s, 1H), 2.35 (d, J=7 Hz, 1H), 2.28 (s, 1H), 1.8–0.95 (m, 6H). 13C NMR (50 MHz, CDCl3)
δ=208.8 (C), 160.1 (CH), 145.9 (C), 128.2 (CH), 126.9 (CH), 54.8 (CH), 47.6 (CH), 39.3 (CH), 38.2
(CH), 31.2 (CH2), 29.0 (CH2), 28.3 (CH2). MS (DIP-CI-NH3) m/e=242 (M++18, 82%), 225 (M++1,
100%), 224 (M+, 4%).
3.17. (1S,2R,6R,7R)-4-Phenyltricyclo[5.2.1.02,6 ]dec-4-en-3-one [(−)-7ce]
The procedure described for (−)-7bf (24 h) starting from (+)-8ce (50 mg, 0.14 mmol) afforded 15
mg (86%, 9% ee by GC) of (−)-7ce. [α]D23=−4.2 (c 1.1 benzene). Conditions for chiral GC analysis:
Cyclodex-β (50 m, 0.25 mm ID) column, 150°C, tR (min)=51.4 (major), 53.4 (minor). Spectroscopic
data identical to those of (+)-7ce.
3.18. Pauson–Khand reaction of (+)-(R)-ethynyl p-tolyl sulfoxide 1d with norbornene
To a solution of 1d (100 mg, 0.6 mmol) in CH2Cl2 (3 mL) was added Co2(CO)8 (205 mg, 0.6 mmol).
After 10 min of stirring at room temperature, norbornene (282 mg, 3 mmol) was added and the mixture
cooled down to −78°C. NMO (211 mg, 1.8 mmol) was added and the mixture was allowed to warm up to
0°C. Then, it was cooled again to −78°C and more NMO (211 mg, 1.8 mmol) was added. The mixture was
allowed to reach room temperature and stirred for 1 h. The crude was evaporated and chromatographed
affording 12 mg (9% yield) of 4de as a mixture of diastereomers (1.2:1 by 13C NMR). IR (film) νmax
1
=2960, 2880, 1700, 1600, cm−1. H NMR (200 MHz, CDCl3) δ=7.95–8 (m, 1H), 7.65, 7.28 (AB, J=8
Hz, 4H), 2.85–2.7 (m, 1H), 2.5–1 (m, 9H), 2.39 (s, 3H). 13C NMR (125.7 MHz, CDCl3) δ=203.7 (C),
163.8 (CH), 142.1 (C, major), 142.2 (C, minor), 129.9 (CH), 125.1 (CH, minor), 124.9 (CH, major),
56.1 (CH, major), 56.0 (CH, minor), 49.2 (CH, major), 48.9 (CH, minor), 39.4 (CH, major), 39.3 (CH,
minor), 38.4 (CH, major), 38.5 (CH, minor), 31.5 (CH2, major), 31.3 (CH2, minor), 29.1 (CH2, major),
29.06 (CH2, minor), 28.1 (CH2, major), 28.1 (CH2, minor), 21.5 (CH3, minor), 21.4 (CH3, major). EM
(CI-NH3) m/e=321 (M++35, 1%), 304 (M++18, 100%), 287 (M++1, 2%).

470
E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
3.19. X-Ray diffraction analysis of 5be-minor
The crytal data for 5be-minor are as follows. Crystal dimensions: 0.7×0.6×0.4 mm. Empirical
formula C21H26O2S. Molecular weight 342.48. The three-dimensional intensity data were collected on
a Enraf Nonius CAD4 diffractometer (λ=0.71069 Å) at 293(2) K yielding 3231 independent reflections.
Calculated density 1.241 g/cm3. Crystal system: triclinic. Space group P1 (No. 2). Lattice parameters:
a=8.690(1) Å, b=10.517(2) Å, c=10.820(1) Å, α=108.35(1)°, β=96.23(1)°, γ=98.18(1)°, V=916.6(2) Å3,
Z=2, F(000)=368. The structure was solved by the direct methods (SHELXS-86)28 and refined by least-
squares on F2 of all reflections (SHELXL-93).29 Data/restraints/parameters: 3230/0/217. Goodness-of-fit
on F2: 1.091. Final R indices[I>2σ(I)]: R(F)=0.0369, Rw(F2)=0.1005. R indices (all data): R(F)=0.0426,
Rw(F2)=0.1062.
3.20. X-Ray diffraction analysis of 5ce-major
The crytal data for 5ce-major are as follows. Crystal dimensions 0.5×0.5×0.2 mm. Empirical formula
C23H22O2S. Molecular weight 362.47. The three-dimensional intensity data were collected on a Enraf
Nonius CAD4 diffractometer (λ=0.71069 Å) at 293(2) K yielding 1894 independent reflections. Cal-
culated density 1.282 g/cm3. Crystal system: orthorhombic. Space group P212121 (No. 19). Lattice
parameters: a=9.984(1) Å, b=10.1864(5) Å, c=18.467(3) Å, V=1878.1(4) Å3, Z=4, F(000)=768. The
structure was solved by the direct method (SHELXS-86)28 and refined by least-squares on F2 of all
reflections (SHELXL-93).29 Data/restraints/parameters: 1894/0/235. Goodness-of-fit on F2: 1.075. Final
R indices [I>2σ(I)]: R(F)=0.0278, Rw(F2)=0.0803. R indices (all data): R(F)=0.0324, Rw(F2)=0.0816.
Acknowledgements
We thank DGICYT (PB95-0265) and CIRIT (1996SGR 00013) for financial support. E. Montenegro
thanks CIRIT (Generalitat de Catalunya) for a pre-doctoral fellowship.
References
1. (a) Pauson, P. L.; Khand, I. U. Ann. N. Y. Acad. Sci. 1977, 295, 2–14. (b) Pauson, P. L. Tetrahedron 1985, 41, 5855–5860.
(c) Schore, N. E. Org. React. 1991, 40, 1–90.
2. (a) Castro, J.; Moyano, A.; Pericàs, M. A.; Riera, A.; Greene, A. E.; Alvarez-Larena, A.; Piniella, J. F. J. Org. Chem.
1996, 61, 9016–9020. (b) Castro, J.; Sorensen, H.; Riera, A.; Morin, C.; Moyano, A.; Pericàs, M. A.; Greene, A. E. J. Am.
Chem. Soc. 1990, 112, 9388–9389. (c) Verdaguer, X.; Moyano, A.; Pericàs, M. A.; Riera, A.; Greene, A. E.; Piniella, J.
F.; Alvarez-Larena, A. J. Organomet. Chem. 1992, 433, 305–310. (d) Castro, J.; Greene, A. E.; Moyano, A.; Pericàs, M.
A.; Poch, M.; Riera, A.; Solà, L.; Verdaguer, X. An. Quim. 1993, 89, 135–136. (e) Bernardes, V.; Verdaguer, X.; Kardos,
N.; Riera, A.; Moyano, A.; Pericàs, M. A.; Greene, A. E. Tetrahedron Lett. 1994, 35, 575–578. (f) Castro, J.; Moyano, A.;
Pericàs, M. A.; Riera, A.; Greene, A. E. Tetrahedron: Asymmetry 1994, 5, 307–310. (g) Tormo, J.; Verdaguer, X.; Moyano,
A.; Pericàs, M. A.; Riera, A. Tetrahedron 1996, 52, 14021–14040. (h) Tormo, J.; Moyano, A.; Pericàs, M. A.; Riera, A. J.
Org. Chem. 1997, 62, 4851–4856.
3. (a) Poch, M.; Valenti, E.; Moyano, A.; Pericàs, M. A.; Castro, J.; De Nicola, A.; Greene, A. E. Tetrahedron Lett. 1990, 31,
7505–7508. (b) Verdaguer, X.; Moyano, A.; Pericàs, M. A.; Riera, A.; Bernardes, V.; Greene, A. E.; Alvarez-Larena, A.;
Piniella, J. F. J. Am. Chem. Soc. 1994, 116, 2153–2154. (c) Bernardes, V.; Kann, N.; Riera, A.; Moyano, A.; Pericàs, M.
A.; Greene, A. E. J. Org. Chem. 1995, 60, 6670–6671.
4. Fonquerna, S.; Moyano, A.; Pericàs, M. A.; Riera, A. Tetrahedron 1995, 51, 4239–4254.
5. (a) Montenegro, E.; Poch, M.; Moyano, A.; Pericàs, M. A.; Riera, A. Tetrahedron 1997, 53, 8651–8664. (b) Montenegro,
E.; Poch, M.; Moyano, A.; Pericàs, M. A.; Riera, A. Tetrahedron Lett. 1998, 39, 335–338.

E. Montenegro et al. / Tetrahedron: Asymmetry 10 (1999) 457–471
471
6. Fonquerna, S.; Moyano, A.; Pericàs, M. A.; Riera, A. J. Am. Chem. Soc. 1997, 119, 10225–10226.
7. (a) Carreño, M. C. Chem. Rev. 1995, 95, 1717–1760. (b) Aversa, M. C.; Barattucci, A.; Bonaccorsi, P.; Giannetto, P.
Tetrahedron: Asymmetry 1997, 8, 1339–1367. (c) Marino, J. P. Pure Appl. Chem. 1993, 65, 667–674. (d) Walker, A.
J. Tetrahedron: Asymmetry 1992, 3, 961–998. (e) Posner, G. H. Acc. Chem. Res. 1987, 20, 72–78. (f) Solladié, G. In
Asymmetric Synthesis; Morrison, J. D., Ed. Academic Press: Orlando, 1983; Vol. 2, pp 157–199.
8. (a) Andersen, K. K. Tetrahedron Lett. 1962, 93–95. (b) Andersen, K. K. J. Org. Chem. 1964, 29, 1953–1956.
9. Kosugi, H.; Kitaoka, M.; Tagami, K.; Takahashi, A.; Uda, H. J. Org. Chem. 1987, 52, 1078–1082.
10. Bickart, P.; Carson, F. W.; Jacobus, J.; Miller, E. G.; Mislow, K. J. Am. Chem. Soc. 1968, 33, 4869–4876.
11. Amaudrut, J.; Pasto, D. J.; Wiest, O. J. Org. Chem. 1998, 63, 6061–6064.
12. (a) Jeong, N.; Chung, Y. K.; Lee, B. Y.; Lee, S. H.; Yoo, S. E. Synlett 1991, 204–206. (b) Shambayati, S.; Crowe, W. E.;
Schreiber, S. L. Tetrahedron Lett. 1990, 31, 5289–5292.
13. Enone 7be had been prepared in racemic form by the Pauson–Khand reaction between norbornene and hexyne: Sugihara,
T.; Yamada, M.; Ban, H.; Yamaguchi, M.; Kaneko, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2801–2804.
14. (a) Villar, J. M.; Delgado, A.; Llebaria, A.; Moretó, J. M. Tetrahedron: Asymmetry 1995, 6, 665–668. (b) Villar, J. M.;
Delgado, A.; Llebaria, A.; Moretó, J. M.; Molins, E.; Miravitlles, C. Tetrahedron 1996, 52, 10525–10546.
15. Solladié, G. Bull. Soc. Chim. Belg. 1990, 99, 837–847.
16. Corey, E. J.; Chaykovski, M. J. Am. Chem. Soc. 1964, 86, 1639–1640.
17. Molander, G. A.; Hahn, G. J. Org. Chem. 1986, 51, 1135–1138.
18. Bravo, P.; Resnati, G.; Viani, F. Gazz. Chim. Ital. 1987, 117, 747–750.
19. (a) Chan, T. H.; Prasad, C. V. C. J. Org. Chem. 1987, 52, 110–119. (b) Magnus, P.; Quagliato, D. A. Organometallics
1982, 1, 1243–1244.
20. Lee, B. Y.; Moon, H.; Chung, Y. K.; Jeong, N. J. Am. Chem. Soc. 1994, 116, 2163–2164.
21. Kim, J. W.; Chung, Y. K. Synthesis 1998, 2, 142–144.
22. (a) Periasamy, M.; Reddy, M. R.; Devasagayaraj, A. Tetrahedron 1994, 50, 6955–6964. (b) Rajesh, T.; Periasamy, M.
Tetrahedron Lett. 1998, 39, 117–118. (c) Lee, B. Y.; Chung, Y. K.; Jeong, N.; Lee, Y.; Hwang, S. H. J. Am. Chem. Soc.
1994, 116, 8793–8794. (d) Chung, Y. K.; Lee, B. Y.; Yeong, N.; Hudecek, M.; Pauson, P. L. Organometallics 1993, 12,
220–223. (e) Smit, V. A.; Kireev, S. L.; Nefedov, O. M.; Tarasov, V. A. Tetrahedron Lett. 1989, 30, 4021–4024.
23. Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E.; Foreman, M. I. J. Chem. Soc., Perkin Trans. 1 1973, 977–981.
24. (a) Derdau, V.; Laschat, S.; Jones, P. G. Heterocycles 1998, 48, 1445–1453. (b) Hay, A. M.; Kerr, W. J.; Kirk, G. G.;
Middlemiss, D. Organometallics 1995, 14, 4986–4988. (c) Bladon, P.; Pauson, P. L.; Brunner, H.; Eder, R. J. Organomet.
Chem. 1988, 355, 449–454.
25. Rayner, D. R.; Gordon, A. J.; Mislow, K. J. Am. Chem. Soc. 1968, 90, 4854–4860.
26. Miller, E. G.; Rayner, D. R.; Thomas, H. T.; Mislow, K. J. Am. Chem. Soc. 1968, 90, 4861.
27. Louis, C.; Mill, S.; Mancuso, V.; Hootelé, C. Can. J. Chem. 1994, 72, 1347–1350.
28. Sheldrick, G. M., SHELXS-86. Crystallographic Computing 3; Sheldrick, G. M.; Krüger, C.; Goddard, R., Eds. Oxford
University Press: Oxford, 1985.
29. Sheldrick, G. M., SHELXL-93. A program for the refinement of crystal structures. Göttingen University, 1993.