Direct Transformations of Ketones to γ-Unsaturated Thiols via [2,3]-Sigmatropic Rearrangement of Allyl Sulfinyl Carbanions: A Combined Experimental and Computational Study

Article abstract of DOI:10.1021/jo991672e

The reaction of a series of ketones with dimsylsodium in dimethyl sulfoxide resulting in the formation of γ-unsaturated thiols was studied experimentally. [2,3]-Sigmatropic rearrangements of β-unsaturated sulfinyl carbanions are involved at the key step o

Full text of DOI:10.1021/jo991672e

2984
J . Org. Chem. 2000, 65, 2984-2995
Dir ect Tr a n sfor m a tion s of Keton es to γ-Un sa tu r a ted Th iols via
[2,3]-Sigm a tr op ic Rea r r a n gem en t of Allyl Su lfin yl Ca r ba n ion s: A
Com bin ed Exp er im en ta l a n d Com p u ta tion a l Stu d y
Andrey A. Fokin,*,† Andrey O. Kushko,† Anton V. Kirij,† Alexander G. Yurchenko,† and
Paul v. R. Schleyer‡
Department of Organic Chemistry, Kiev Polytechnic Institute, 37 Pobeda Ave. 252056, Kiev, Ukraine, and
Computational Chemistry Annex, University of Georgia, Athens, Georgia 30602-2525
Received October 25, 1999
The reaction of a series of ketones with dimsylsodium in dimethyl sulfoxide resulting in the
formation of γ-unsaturated thiols was studied experimentally. [2,3]-Sigmatropic rearrangements
of â-unsaturated sulfinyl carbanions are involved at the key step of those transformations. DFT
computations at the B3LYP/6-31+G* level indicated that such rearrangements, as well as some
typical [2,3]-sigmatropic rearrangements, e.g., thermal rearrangements of allyl sulfoxides and Wittig
rearrangements of sulfur ylides and lithiated allyloxy methyl anions, are concerted and moderately
synchronous processes. Negative (diatropic) nucleus-independent chemical shifts (NICS) and high
diamagnetic susceptibility exaltations indicate that the transition structures of these [2,3]-
sigmatropic migrations are aromatic.
Sch em e 1. Ad d ition of DMSS to Keton es
In tr od u ction
Sulfinyl carbanions play an important role in the
chemistry of sulfur compounds.1 The simplest and the
most widely used example, dimsylsodium (DMSS, methyl
sulfinyl carbanion), was discovered over 30 years ago by
Corey.2 This reagent is a strong base3 that can deproto-
nate different CH acids, such as sulfonium, sulfoxonium4
and phosphonium salts.5 Besides, DMSS is rather power-
ful nucleophile which undergoes addition and substitu-
tion reactions with electrophilic substrates. Best known
is the reaction of DMSS with carbonyl compounds to give
â-hydroxy sulfoxides (Scheme 1).2 Addition usually pro-
ceeds under mild conditions (25 °C or lower) and does
not require high temperatures.
DMSS in dimethyl sulfoxide (DMSO) is considered6 to
decompose rapidly at temperatures above 80 °C; hence,
reactions at higher temperatures have received little
attention. However, we have demonstrated that dimethyl
sulfoxonium methylide reacts with ketones in DMSO at
120 °C to give substituted 1,3-dienes with high prepara-
tive yields.7 In this paper, we describe the unusual
reaction of ketones with DMSS in DMSO at temperatures
Sch em e 2. γ-Un sa tu r a ted Th iol F or m a tion in th e
DMSS/DMSO System
above 120 °C. We show that this transformation can be
used for the preparation of homoallyl thiols. The key step,
a new [2,3]-sigmatropic rearrangement of allyl sulfinyl
carbanions, has been studied computationally, together
with some other typical [2,3]-sigmatropic migrations used
as model reactions.
Exp er im en ta l Resu lts
On e-Step Tr a n sfor m a tion s of Keton es to Hom o-
a llyl Th iols in DMSS/DMSO System . The interaction
of DMSS with a number of aliphatic, cyclic, and cage
ketones (Table 1) in DMSO in the 125-130 °C temper-
ature range resulted in the formation of the correspond-
ing γ-unsaturated thiols (Scheme 2).8
† Kiev Polytechnic Institute.
‡ University of Georgia.
(1) (a) Krief, A. Tetrahedron 1980, 36, 2531. (b) Field, L. Synthesis
1972, 101. (c) Barrett, G. C. Rodd’s Chem. Carbon Compd., 2nd ed.;
1996; Vol. 3, Part A.
The best results (Table 1) were obtained for aliphatic
and cyclic ketones. Relatively low yields of compounds
16-18 can be attributed to the steric factors. In the case
of octanone-2 (3) and (1-adamantyl)acetone (8), the
products arising from the mercaptomethylation of the
methyl group are formed preferably. In summary, we
have found a new preparative method for direct trans-
(2) (a) Corey E. J .; Chaykovsky M. J . Am. Chem. Soc. 1965, 87, 1345.
(b) Corey E. J .; Mitra R. B.; Uda H. J . Am. Chem. Soc. 1964, 86, 485.
(3) (a) Becker, H.-D.; Russell, G. A. J . Org. Chem. 1963, 28, 1896.
(b) Russell, G. A.; Becker, H.-D. J . Am. Chem. Soc. 1963, 85, 3406. (c)
Cardenas, C. G.; Khafaji, A. N.; Osborn, C. L.; Gardner P. D. Chem.
Ind. 1965, 345. (d) Osborn, C. L.; Shields, T. C.; Shoulders, B. A.;
Cardenas, C. G.; Gardner, P. D. Chem. Ind. 1965, 766. (e) Roberts,
W.; Whiting, M. C. J . Chem. Soc. 1965, 1290. (f) Argabright, P. A.;
Hofmann, J . E.; Schriesheim, A. J . Org. Chem. 1965, 30, 3233. (g)
Russell, G. A.; Weiner S. A. J . Org. Chem. 1966, 31, 248.
(4) Claus, P. K. Schwefel-Ylide; Houben-Weyl, Board E11, S.1344,
1985.
(7) Yurchenko, A. G.; Kirij, A. V.; Likhotvorik, I. R.; Melnik, N. N.;
Zaharzh, P.; Bzezovsky, V. V.; Kushko, A. O. Synthesis 1991, 5, 393.
(8) Kushko, A. O.; Yurchenko, A. G.; Kirij, A. V.; Likhotvorik, I. R.;
Fokin, A. A. J . Org. Chem. Russ. 1998, 34, 776.
(5) J ohnson, A. W. Ylides and Imines of Phosphorus; J ohn Wiley &
Sons: New York, 1993.
(6) Corey, E. J .; Chaykovsky, M. J . Am. Chem. Soc. 1965, 87, 1353.
10.1021/jo991672e CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/14/2000

Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2985
Ta ble 1. Str u ctu r e a n d Yield s of Hom oa llylth iols 10-18
Obta in ed fr om th e Rea ction of Keton es 1-9 w ith Dim syl
Sod iu m in DMSO
Sch em e 3. Tr a n sfor m a tion s of Cycloh exa n on e 4
in th e DMSS/DMSO System
temperatures as described previously for the tertiary
alcohols.10 If DMSS is used in a small excess or in an
equimolar amount relative to ketone, the intermediate
sulfoxide B undergoes a thermal [2,3]-O-sigmatropic
rearrangement to give allylic alcohol C. Similar trans-
formations were studied previously using unsaturated
arylsulfoxides.12 Unsaturated sulfoxide B,13 indepen-
dently prepared, also formed allylic alcohol C in DMSO
when heated at 125-130 °C. With excess DMSS, depro-
tonation of B occurs; carbanion D, thus formed, under-
goes [2,3]-C-sigmatropic rearrangement to the unstable
sulfenic acid anion E. The latter forms 13 after the
reduction in DMSO.14
Thus, one-pot formation of the desired 13 occurs due
to the remarkable properties of the DMSS/DMSO system,
which acts both as an nucleophile and as a base (addition
to 4 and deprotonation of B) and also dehydrates A to B.
There also are some interesting features in the Scheme
3. The dehydration of A gives B, rather than the
conjugated isomer F . The second question is the inter-
mediacy of the carbanion G, which, unlike D, is stabilized
both by the sulfinyl group and by the CC double bond.
Even if we find that G is more stable than D, the
observed rearrangement must proceed from D as an
formation of ketones to homoallyl thiols9 applicable to a
wide range of substrates.
Scheme 3 summarizes the reaction of DMSS with
cyclohexanone 4, as a model compound. The key steps of
these transformations were confirmed by a series of
model experiments. The excess of the base (DMSS) was
found to be decisive factor in determining the reaction
course. Thus, thiol 13 is formed from 4 with a high yield
(71%) only with a 3-fold DMSS excess, whereas the
reaction with a 1.2-1.5-fold DMSS excess results in the
formation of allylic alcohol C with a yield of 73%.10
â-Hydroxysulfoxide A,11 presumably formed in the first
step of the reaction, dehydrates in DMSO at elevated
(12) (a) Hoffmann, R. W.; Goldmann, S.; Maak, N.; Gerlach, R.;
Frickel, F.; Steinbach, G. Chem. Ber. 1980, 113, 819. (b) Goldmann,
S.; Hoffmann, R. W.; Maak, N.; Geueke, K.-J . Chem. Ber. 1980, 113,
831. (c) Hoffmann, R. W.; Goldmann, S.; Gerlach, R.; Maak, N. Chem.
Ber. 1980, 113, 845. (d) Hoffmann, R. W.; Gerlach, R.; Goldmann, S.
Chem. Ber. 1980, 113, 856.
(13) Unsaturated sulfoxide B was obtained independently by method
described elsewhere.10 The rearrangement of B into allylic alcohol C
in DMSO/KOH was also previously demonstarted.10
(9) (a) Miyata, O.; Shinada, T.; Ninomiya, I.; Naito, T. Tetrahedron
1997, 53, 2421. (b) Nishio, T.; Kato, M. J . Heterocycl. Chem. 1997, 34,
143. (c) Kang, J .; Kim, J . W.; Lee, J . W.; Kim, D. S.; Kim, J . E. Bull.
Korean Chem. Soc. 1996, 17, 1135. (d) Haque, M. B.; Roberts, B. P.
Tetrahedron Lett. 1996, 37, 9123. (e) Montenegro, E.; Echarri, R.;
Claver, C.; Castillon, S.; Moyano, A.; Pericas, M. A.; Riera, A.
Tetrahedron: Asymmetry 1996, 7, 3553.
(10) Trofimov, B. A.; Petrova, O. V.; Vasiltsov, A. M.; Mikhaleva, A.
I. Izv. AN USSR, Ser. Khim. 1990, 1601.
(14) (a) Hogg, P. R.; Stewart, I. J . Chem. Soc., Perkin Trans. 2 1974,
436. (b) Allison, W. S. Acc. Chem. Res. 1976, 9, 293. (c) Cooper, R. D.;
J ose, G. J . Am. Chem. Soc. 1970, 92, 2575. (d) Allan, R. D.; Barton, D.
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1 1974, 1456.
(11) The transformation of independently prepared10 â-hydroxysulf-
oxide
A under similar reaction conditions increase the yield of
corresponding homoallylic thiol 13 by 5-10% on the average.

2986 J . Org. Chem., Vol. 65, No. 10, 2000
Fokin et al.
Sch em e 4. [2,3]-Sigm a tr op ic Rea r r a n gem en t of
Cycloh exen -1-yl DMSO in th e P r esen ce of Ba se
reliability of the B3LYP method was confirmed by
comparison with the MP2/6-31+G* energies for key
transformations. Reaction pathways along both directions
from the transition structures were followed by the IRC
method. The ZPVEs were scaled by a factor of 0.98 for
energy corrections at the B3LYP/6-311+G**//B3LYP/6-
31+G* level.
The synchronicities (Sy)17 of sigmatropic reactions have
been calculated via eq 1:18
n
|δBi - δBav|
Sy ) 1 - (2n - 2)-1
BTi S - BRi
(1)
∑
δBav
i)1
n
δBi )
δBav ) n-1 δB
∑
i
BPi - BRi
intermediate. Also, the positive counterion can play an
important role in the stabilization of carbanions; the
structures and the relative stabilities of these species will
be studied computationally in this paper.
i)1
where n is the number of the bonds involved in the
reaction (n ) 5 for [2,3]-sigmatropic reaction), BTi S, BiR,
and BPi are Wiberg bond indices19 for the i-bond in the
transition structure (TS), reactant (R), and product (P),
respectively. According to this definition, if all bonds in
the TS are broken or formed to the same extent the
reaction is synchronous and Sy ) 1. In contrast, Sy ) 0 if
at least one bond involved into the rearrangement is
unchanged in the TS relative to the starting minimum.
The natural bond orbital (NBO) method20 was used for
the Bi computations.
Nucleus-independent chemical shifts (NICS)21 and
magnetic susceptibilities ø were computed with the
continuous set of gauge transformations (CSGT) method
at the B3LYP/6-311+G**//B3LYP/6-31+G* level. NICS
are based on the magnetic shielding computed at the
centers of the rings; negative (upfield) NICS values
indicate diatropic ring currents and the electron delocal-
ization. Magnetic susceptibility exaltations Λ were esti-
mated as the differences in the magnetic susceptibilities
(ø), computed for the ground and transition states. To
analyze σ and π contributions to the ring shieldings,
dissected NICS were computed at the IGLO-III TZ2P
level using the Pipek and Mezey localization procedure22
as implemented in the deMon-Master program.23
Th e [2,3]-Sigm a tr op ic Rea r r a n gem en t of B to 13
in th e P r esen ce of Ba se. When treated with the DMSS
in DMSO, the independently prepared13 unsaturated
sulfoxide B also formed thiol 13 (81% yield). We extended
our studies to other reacting systems, which are different
from the DMSS/DMSO. With the n-BuLi in ether fol-
lowed by the reductive workup with LiAlH4, B was also
converted with high yield to the thiol 13 (Scheme 4). The
key step of this transformation includes a [2,3]-sigma-
tropic rearrangement of unsaturated sulfinyl carbanion
D in the presence of base.
To gain the additional information on the mechanism,
this [2,3]-sigmatropic rearrangement as well as some
related [2,3]-sigmatropic migrations were studied theo-
retically.
Com p u ta tion a l Meth od s
All calculations were performed at the density func-
tional theory (DFT) level using Becke’s three-parameter
hybrid method with LYP correlational functional (B3LYP)
as implemented in the Gaussian 9415 and Gaussian 9816
program packages. The 6-31+G* basis set was used for
the geometry optimizations and for characterization of
the stationary points by frequency analysis (NIMAG )
0 for minima and 1 for transition structures). The
Com p u ta tion a l Resu lts
Since the [2,3]-sigmatropic reactions are widely used
in organic synthesis, there have been many recent
computational studies.24 A typical example, the [2,3]-
(15) (a) Foresman, J . B.; Frisch, M. Exploring Chemistry with
Electronic Structure Mehods; Gaussian, Inc.: Pittsburgh, 1996. (b)
Density functional theory computations were carried out with the
Gaussian 94 program. Gaussian 94, Revision D.2: Frisch, M. J .;
Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; J ohnson, B. G.; Robb,
M. A.; Cheeseman, J . R.; Keith, T. A.; Petersson, G. A.; Montgomery,
J . A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J .
V.; Foresman, J . B.; Cioslowski, J .; Stefanov, B. B.; Nanayakara, A.;
Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;
Andres, J . L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J .;
Binkley, J . S.; Defrees, D. J .; Baker, J .; Stewart, J . P.; Head-Gordon,
M.; Gonzalez C.; Pople, J . A. Gaussian, Inc., Pittsburgh, PA, 1995.
(16) Gaussian 98, Revision A.5: Frisch, M. J .; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J . R.;
Zakrzewski, V. G.; Montgomery, J r., J . A.; Stratmann, R. E.; Burant,
J . C.; Dapprich, S.; Millam, J . M.; Daniels, A. D.; Kudin, K. N.; Strain,
M. C.; Farkas, O.; Tomasi, J .; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J .;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.; Cioslowski, J .; Ortiz,
J . V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P.
M. W.; J ohnson, B.; Chen, W.; Wong, M. W.; Andres, J . L.; Head-
Gordon, M.; Replogle, E. S.; Pople, J . A. Gaussian, Inc., Pittsburgh,
PA, 1998.
(17) Moyano, A.; Perica`s, M. A.; Valent´ı, E. J . Org. Chem. 1989, 54,
573.
(18) (a) Lecea, B.; Arrietta, A.; Roa, G.; Ugalde, J . M.; Coss´ıo, F.
P.J . Am. Chem. Soc. 1994, 116, 9613. (b) Coss´ıo, F. P.; Morao, I.; J iao,
H.; Schleyer, P. v. R. J . Am. Chem. Soc. 1999, 121, 6737.
(19) Wiberg, K. B. Tetrahedron 1968, 24, 1083.
(20) Reed, A. E.; Curtiss, L. A.; Weinhold, F. J . Chem. Rev. 1988,
88, 899.
(21) (a) J iao, H.; Schleyer, P. v. R. Angew. Chem., Int. Ed. Engl.
1996, 35, 2373. (b) Subramanian, G.; Schleyer, P. v. R.; J iao, H. Angew.
Chem., Int. Ed. Engl. 1996, 35, 2824. (c) J iao, H.; Schleyer, P. v. R.;
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Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2987
Sch em e 5. Selected Exa m p les of
[2,3]-Sigm a tr op ic Rea ction s
Sch em e 6. Rela tive En er gies of th e Con for m er s
a n d [2,3]-Rea r r a n gem en ts of ASC (in k ca l/m ol
fr om B3LYP /6-311+G**//B3LYP /6-31+G* (∆E) a n d
B3LYP /6-311+G**//B3LYP /6-31+G* + ∆ZP VE (∆E0)
Da ta )
Wittig rearrangement25 of the allyloxy methylene anion
to the homoallylic alcoholate anion (Scheme 5, eq 2), is
generally accepted to be a concerted sigmatropic reac-
tion.26 However, this is not found for the parent nonsta-
bilized allyoxymethyl anion where the computed transi-
tion structure is extremely early and describes the
carbanion inversion and the C-O bond dissociation.
When the carbanion is stabilized by a ethynyl substituent
the transition structure is quite different and does
describe a true concerted reaction pathway (the [2,3]-
migration barrier is 6.0 kcal/mol at MP2/6-31+G*).27
Likewise, if a Li+ counterion is included in the TS, the
barrier of the concerted reaction is 16.2 kcal/mol at MP2/
6-31+G.28
A key step of another convenient route to allylic
alcohols involves the stereoselective [2,3]-sigmatropic
Mislow-Evans rearrangement of allyl sulfoxides (Scheme
5, eq 3) to unstable sulfenates.29 The experimentally
observed stereoselectivities and activation energies were
reproduced recently by ab initio calculations (the barriers
are 26-28 kcal/mol for 1,2-dimethylallyl phenyl sulfoxide
rearrangement30 and 16 kcal/mol for allyl sulfoxide
rearrangement31 at the different MP correlated levels).
The [2,3]-Wittig rearrangement also have been ex-
tended to allylic sulfur ylides and used for the selective
preparations of sulfides (Scheme 5, eq 4).32 Computations
by J ursic33 at HF and by Wu and Houk34 at correlated
MP2 and MP3 levels with the 6-31+G* basis set pre-
dicted concerted mechanisms with the barriers about 10-
16 kcal/mol for [2,3]-sigmatropic migration in sulfur allyl
ylides.
The allyl sulfinyl carbanion (ASC) is used here as a
model for computational studies of our [2,3]-sigmatropic
rearrangement (Scheme 5, eq 5). The influence of alkyl
substitution is studied with the crotyl sulfinyl (CSC, eq
6) and the 2-methylallyl sulfinyl carbanions (MSC, eq 7).
A set of parent reactions, including the classical [2,3]-
Wittig rearrangement of the allyl methylene ether anion
to the homoallylic alcoholate anion (eq 2) as well as the
rearrangement of the allyl methyl sulfoxide to the meth-
ylsulfenic acid allylic ether (eq 3), and the Wittig rear-
rangement of allylsulfonium methylide to methylhomo-
allyl sulfide (eq 4), also are computed in order to provide
a more comprehensive mechanistic overview of [2,3]-
sigmatropic migrations.
(24) (a) Houk, K. N.; Li, Y.; Evansek, J . D. Angew. Chem., Int. Ed.
Engl. 1992, 31, 682. (b) Wiest, O.; Montiel, D. C.; Houk, K. N. J . Phys.
Chem. A 1997, 101, 8378. (c) Harmata, M.; Glaser, R.; Chen, G. S.
Tetrahedron Lett. 1995, 36, 9145. (d) Okajima, T.; Fukazawa, Y. Chem.
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J . J . Am. Chem. Soc. 1988, 110, 2925.
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1983, 48, 279. (b) Takanishi, T.; Nemoto, H.; Kanda, Y.; Tsuji, J .;
Fukazawa, Y.; Okajima, T.; Fujise, Y. Tetrahedron 1987, 43, 5499.
(27) Mikami, K.; Uchida, T.; Hirano, T.; Wu, Y.-D.; Houk, K. N.
Tetrahedron 1994, 20, 5917.
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55, 1421.
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[2,3]-Sigm a tr op ic Rea r r a n gem en ts in Allyl Su lfi-
n yl Ca r ba n ion s. Con for m a tion s of ASC. Intercon-
versions of the different ASC conformers (MIN1-MIN8)
are depicted in Scheme 6 (for optimized geometries and
absolute energies see Figure 1 and Table 2, respectively).
The most stable is anti conformer MIN1, where reacting
centers (double bond and carbanion) are quite distant,
although the differences in energies with other conform-
ers are low (2-3 kcal/mol). Conformers can interconvert
via rotation around C-S bond or carbanion inversion.35
Rotation via TS1-3, TS2-4, TS5-6, and TS7-8 (Figure
2) requires 3-5 kcal/mol and the inversion of the car-
(31) J ursic, B. S.THEOCHEM 1995, 358, 131.
(32) (a) Kido, F.; Sinha, S. C.; Abiko, T.; Yoshikoshi, A. Tetrahedron
Lett. 1989, 30, 1575. (b) Hoffmann, R. W. Angew. Chem., Int. Ed. Engl.
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(34) Wu, Y.-D.; Houk, K. N. J . Org. Chem. 1991, 56, 5657.

2988 J . Org. Chem., Vol. 65, No. 10, 2000
Fokin et al.
endo (TS8-10) transition structures were located (Figure
2); the IRC procedure indicated that both TSs are
connected with reactants in the antiperiplanar conforma-
tions of the carbanions (MIN4 and MIN8).
Sigmatropic migrations with the inversion of the
carbanions and rotation around the C-S bonds proceed
with the formation of C-C and the breaking of C-S
bonds; in the TSs both of these bond distances are 2.7-
2.8 Å (Figure 2). The barriers of[2,3]-sigmatropic shifts
in ASC are extremely low: 0.5 kcal/mol in MIN4 and 0.9
kcal/mol in MIN8.36 The geometries of the allylic moieties
in the TSs are distorted relative to the free C2v allyl
anion: the deviations of the CH2 groups from the CCC
plane are 10-15°and the CCC fragment is compressed
relative to the free allyl anion37 (126° vs 133°). The
negative charge is delocalized strongly in these TSs: only
about 0.5e of the total is located on the allylic moieties.
The molecular fragments in the ASC transition struc-
tures are strongly bound: the dissociation energies to free
H2CdSO and the allyl anion are high (24.4 kcal/mol for
TS4-9 and 23.8 kcal/mol for TS8-10).
A more realistic picture of the [2,3]-sigmatropic rear-
rangement in sulfinyl carbanions, includes the Li+ coun-
terion in the ASC rearrangement (Scheme 7).
In the presence of the Li+, the reaction is still exother-
mic (-22.6 and -21.1 kcal/mol) but the barriers increase
(23.0 and 22.3 kcal/mol) relative to free ASC (see Scheme
6). The geometries of the TSs also change significantly:
partially formed/broken bonds are much shorter (Figure
2) when Li+ is included (from 2.4 to 2.5 Å vs 2.7 to 2.8 Å
for free ACS rearrangement).38 The molecular fragments
in the TSs are more tightly bound, i.e., B23 and B15 values
(see Table 3) increases (the ASC transition structures are
described in more detail below).
[2,3]-Sigm a tr op ic Sh ifts in Meth yl-Su bstitu ted
ASC. The [2,3]-sigmatropic shifts in CSC (MIN11 and
MIN13) and MSC (MIN15 and MIN17), both of which
have anti-periplanar conformations of the carbanion
moieties, are shown in Scheme 8; the optimized geom-
etries are depicted in Figure 3. The influence of methyl
substitution on the barriers of exo-migrations via TS11-
12 (1.0 kcal/mol) and TS15-16 (1.2 kcal/mol) is small,
and the relative barriers are similar to the unsubstituted
ASC. The methyl substituents influence the geometries,
but not the relative energies of the TSs (Figure 3).
Computations on the CSC and MSC rearrangements
clearly indicate that alkyl substitution generally has only
a small influence on the [2,3]-sigmatropic migrations in
allyl sulfinyl carbanions.
[2,3]-Sigm a tr op ic Migr a tion s in th e Cycloh exen -
1-yl Meth yl Su lfin yl Ca r ba n ion . The experimental
results on the rearrangement of unsaturated sulfoxide
B (Scheme 2) were verified computationally. The dehy-
dration of the alcohol A (Scheme 2) gives the endocyclic
olefin B (Scheme 2 and eq 8) rather than the terminal
olefin F (the latter is 3.0 kcal/mol less stable at DFT, eq
8, relative energies in kcal/mol from B3LYP/6-311+G**//
B3LYP/6-31+G* (∆E) and B3LYP/6-311+G**//B3LYP/6-
31+G* + ∆ZPVE (∆E0) data). The R-deprotonation of the
F igu r e 1. B3LYP/6-31+G*-optimized geometries of ASC
minima.
banions via TS1-2, TS3-4, TS5-7, and TS6-8 (Figure
2) less than 1.0 kcal/mol.
The C-S bond distances depend strongly on the
conformations of the carbanion moieties. Due to the
considerable hyperconjugative interactions, the C-S
bonds are elongated substantially (2.01-2.15 Å, Figure
1) in anti-periplanar conformations of MIN2, MIN4,
MIN7, and MIN8, vs 1.89-1.92 Å in syn-periplanar
forms, MIN1, MIN3, MIN5, and MIN6. The proximate
minima MIN3 and MIN4 considered as starting struc-
tures for exo-[2,3]-sigmatropic migrations in ASC; direct
endo-migrations are possible only from MIN6 or MIN8.
[2,3]-Sigm a tr op ic Sh ifts in ASC. The [2,3]-sigma-
tropic rearrangements of the ASC to conformeric allyl
sulfinyl anions (MIN9 and MIN10, Scheme 6) are 25-
30 kcal/mol exothermic (at B3LYP/6-311+G**//B3LYP/
6-31+G* and at MP2/6-31+G*). Both exo (TS4-9) and
(36) Similar barriers (1.2 and 1.5 kcal/mol) were computed for these
reactions at MP2/6-31+G* level.
(37) Schleyer, P. v. R. J . Am. Chem. Soc. 1985, 107, 4793.
(38) We found analogues transition structures including one explicit
solvent molecule (dimethyl ether) in TS4-9 and TS8-10 modeling
[2,3]-sigmatropic rearrangement of ASC in solution; this lowers the
barriers to 21.3 and 20.5 kcal/mol, respectively.
(35) Conformers can also interconvert via rotation of the allyl group,
however the barriers are slightly higher (4-6 kcal/mol) than the
barriers of the CH2SO group rotation.

Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2989
Ta ble 2. Com p u ted Absolu te En er gies (E, a u ), Zer o-P oin t Vibr a tion a l En er gies (ZP VE, k ca l/m ol), a n d Nu m ber of th e
Im a gin a r y Mod es (NIMAG) for Op tim ized Str u ctu r es
E,
E,
E,
B3LYP/
ZPVE
E,
B3LYP/
ZPVE
B3LYP/
6-31+G*
6-311+G**//
B3LYP/6-31+G*
(NIMAG)
B3LYP/6-31+G*
B3LYP/
6-31+G*
6-311+G**//
B3LYP/6-31+G*
(NIMAG)
B3LYP/6-31+G*
structure
structure
MIN1
MIN2
MIN3
MIN4
MIN4Li
MIN5
MIN6
MIN7
MIN8
629.98890
629.98674
629.98428
629.98577
637.54502
629.98847
629.98619
629.98507
629.98583
637.54546
630.03456
637.58284
630.03798
637.58064
669.30321
669.35053
669.30334
669.35248
669.30516
669.35352
669.30584
669.35403
594.63608
630.59489
239.32890
594.72583
630.60471
239.40855
786.65870
630.07636
630.07448
630.07207
630.07404
637.63420
630.07609
630.07369
630.07315
630.07405
637.63457
630.12084
637.67226
630.12412
637.66997
669.40006
669.44656
669.40064
669.44825
669.40267
669.44916
669.40362
669.44995
594.71509
630.68099
239.39373
594.80313
630.69134
239.47184
786.77944
61.77 (0)
60.66 (0)
61.43 (0)
60.75 (0)
64.43 (0)
61.78 (0)
61.83 (0)
60.77 (0)
60.96 (0)
64.56 (0)
63.24 (0)
65.70 (0)
63.42 (0)
65.67 (0)
78.47 (0)
80.91 (0)
78.72 (0)
81.20 (0)
78.43 (0)
81.19 (0)
78.68 (0)
81.12 (0)
84.39 (0)
70.93 (0)
63.69 (0)
86.73 (0)
71.32 (0)
64.94 (0)
130.13 (0)
D
E
F
G
D-Li
E-Li
G-Li
786.04559
786.09244
786.65494
786.06412
793.60832
793.63924
793.61412
786.03804
793.56488
629.98671
629.98314
629.98304
629.98403
629.97954
629.98492
629.98497
629.98237
629.98104
637.50443
629.98205
637.50592
669.29786
669.29671
669.29985
669.29888
594.63107
630.56710
239.30462
786.16809
786.21367
786.77518
793.73647
793.73187
793.76386
793.73647
786.16211
793.69008
630.07438
630.07096
630.07152
630.07193
630.06721
630.07286
630.07283
630.07085
630.07203
637.59535
630.07109
637.59668
669.39695
669.39585
669.39908
669.39822
594.71104
630.65461
239.37083
119.97 (0)
122.51 (0)
130.47 (0)
120.77 (0)
123.70 (0)
125.95 (0)
123.41 (0)
118.85 (1)
122.65 (1)
60.83 (1)
61.56 (1)
60.58 (1)
60.91 (1)
61.53 (1)
60.67 (1)
60.49 (1)
60.42 (1)
59.91 (1)
63.05 (1)
59.90 (1)
63.18 (1)
77.44 (1)
77.50 (1)
77.36 (1)
77.43 (1)
83.83 (1)
70.19 (1)
62.03 (1)
TSD-E
TSD-E-Li
TS1-2
TS1-3
TS2-4
TS3-4
TS5-6
TS5-7
TS6-8
TS7-8
TS4-9
TS4-9Li
TS8-10
TS8-10Li
TS11-12
TS13-14
TS15-16
TS17-18
TS19-22
TS20-23
TS21-24
MIN8Li
MIN9
MIN9Li
MIN10
MIN10Li
MIN11
MIN12
MIN13
MIN14
MIN15
MIN16
MIN17
MIN18
MIN19
MIN20
MIN21
MIN22
MIN23
MIN24
B
F igu r e 2. B3LYP/6-31+G*-optimized geometries for ASC transition structures.
unsaturated sulfoxide B from the CH2 group is more
minimum of suitable for [2,3]-sigmatropic rearrangement
favorable than from the CH3 group: the proximate
structure (D) is 9.8 kcal/mol less stable than the isomeric

2990 J . Org. Chem., Vol. 65, No. 10, 2000
Fokin et al.
Ta ble 3. Bon d In d ices (Bi), Nu cleu s-In d ep en d en t Ch em ica l Sh ifts (NICS, p p m -cgs), Ma gn etic Su scep tibility Exa lta tion s
(Λ, p p m -cgs) for TSs, a n d Syn ch r on icities (Sy) Com p u ted for Som e [2,3]-Sigm a tr op ic Rea ction s
b
c
c
NICSb
NICSt
NICSσ
NICSπ
CSGT-B3LYP/
6-311+G**
IGLO-III
TZ2P
IGLO-III
TZ2P
IGLO-III
TZ2P
a
structure
B12
B23
B34
B45
B15
δBav
Λd
Sy
TS4-9
1.44
1.26
1.44
1.27
1.43
1.42
1.44
1.43
1.40
1.16
1.21
0.22
0.32
0.20
0.34
0.24
0.23
0.22
0.19
0.41
0.37
0.36
1.49
1.49
1.51
1.47
1.46
1.47
1.45
1.48
1.31
1.48
1.35
1.53
1.49
1.51
1.50
1.52
1.50
1.49
1.47
1.70
1.47
1.64
0.14
0.34
0.22
0.35
0.19
0.21
0.20
0.22
0.20
0.33
0.24
0.32
0.55
0.38
0.52
0.35
0.36
0.35
0.40
0.23
0.85
0.64
-14.8
-19.1
-16.6
-20.0
-15.0
-16.3
-16.3
-16.8
-16.7
-22.6
-18.7
-16.2
-19.9
-17.0
-21.1
-15.0
-16.7
-16.4
-17.1
-17.3
-23.6
-19.8
-4.1
-3.0
-4.1
-3.0
-3.1
-3.8
-3.7
-4.1
-6.5
-4.4
-2.9
-9.1
-12.8
-9.0
-13.3
-9.5
-9.9
-9.4
-9.5
-5.2
-11.2
-9.8
-11.2
-14.7
-8.8
0.71
0.84
0.77
0.87
0.78
0.78
0.77
0.76
0.61
0.57
0.59
TS4-9Li
TS8-10
TS8-10Li
TS11-12
TS13-14
TS15-16
TS17-18
TS19-22
TS20-23
TS21-24
-15.4
-9.6
-8.7
-12.2
-9.1
-11.4
-12.0
-10.0
a
b
Atom numbering as in Figures 2, 3, and 5. NICS total. c The sum of the contributions only from the σ- and π-bonds in five-membered
d
rings without the contributions from the other bonds of the TSs. Calculated as a difference between magnetic susceptibilities (ø) of the
transition structure and reactant.
Sch em e 7. [2,3]-Sigm a tr op ic Rea r r a n gem en t in
th e Com p lex of th e ASC w ith Li+
Sch em e 8. [2,3]-Sigm a tr op ic Sh ift in
Meth yl-Su bstitu ted ASC (Rela tive En er gies in
k ca l/m ol fr om B3LYP /6-311+G**//B3LYP /6-31+G*
(∆E) a n d B3LYP /6-311+G**//B3LYP /6-31+G* +
∆ZP VE (∆E0) Da ta )
conjugated carbanion G (eq 9). However, when a Li+
counterion is present, the relative stabilities changed
dramatically: localized structure D-Li has nearly the
same stability as conjugated carbanion G-Li (eq 10).
Thus, computations show that the possible starting
minimum for [2,3]-sigmatropic migration (D, Scheme 2
and eq 9) is stabilized more by the counterion than the
alternative isomeric carbanion G and the rearrangement
via D can proceed efficiently in n-BuLi/ether or DMSS/
DMSO reacting systems.
The [2,3]-sigmatropic rearrangements in D also were
computed (Scheme 9) and follow the same trends found
for substituted ASCs: the reaction is exothermic (-26.1
kcal/mol), and the barrier of the rearrangement is low
(2.6 kcal/mol). The geometry of five-membered ring in the
TSD-E (Figure 4) are also similar to ASC case.
With the Li+ added to cyclohexen-1-yl sulfinyl carban-
ion (D-Li) the barrier of the rearrangement increases
(25.1 kcal/mol) and the geometry of the five-membered
ring in the TSD-E-Li is similar to the TS4-9Li of the
[2,3]-sigmatropic migration in ASC. Thus, computations
on a larger systems confirmed that the substitution
influent only slightly on the [2,3]-sigmatropic shifts in
the allyl sulfinyl carbanions.
man,41 pericyclic reactions occur concertely via transition
states that have aromatic character. The nature of the
transition structures of some pericyclic reactions recently
has been analyzed systematically for some cycloaddition
reactions, Cope and Claisen rearrangements, and H-
shifts.42 Strongly exalted diamagnetic susceptibilities (Λ)
as well as high negative NICS values were shown to be
associated with the aromaticity of the transition struc-
Com p a r in g w ith Typ ica l [2,3]-Sigm a tr op ic Mi-
gr a tion s. In accord with the Woodward-Hoffmann
rules39 as well as the concepts of Evans40 and Zimmer-
(41) Zimmerman, H. Acc. Chem. Res. 1971, 4, 272.
(42) (a) J iao, H.; Schleyer, P. v. R. Angew. Chem., Int. Ed. Engl.
1993, 32, 1763. (b) J iao, H.; Schleyer, P. v. R. J . Chem. Soc., Perkin
Trans. 1994, 407. (c) Herges, R.; J iao, H.; Schleyer, P. v. R. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1376. (d) J iao, H. Schleyer, P. v. R.
Angew. Chem., Int. Ed. Engl. 1994, 34, 334. (e) J iao, H.; Schleyer, P.
v. R. J . Am. Chem. Soc. 1995, 117, 11529. (f) J iao, H.; Schleyer, P. v.
R. J . Phys. Org. Chem. 1998, 11, 655.
(39) Woodward, R. B.; Hoffmann, R. The Conservation of the Orbital
Symmetry; Verlag Chemie: Weinheim, 1970.
(40) Evans, M. G.; Polanyi, M. Trans. Faraday Soc. 1938, 34, 11.

Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2991
F igu r e 3. B3LYP/6-31+G*-optimized geometries for methyl-substituted ASC.
The [2,3]-sigmatropic migrations in allyl sulfonium
methylide (MIN19) to methyl homoallyl sulfide (MIN22)
is more exothermic (-52.9 kcal/mol) than the allyl methyl
sulfoxide (MIN20) rearrangement (6.1 kcal/mol) to allyl
methyl sulfenate (MIN23). As expected from Hammond
postulate,43 the first highly exothermic reaction is char-
acterized by an earlier TS19-22 with only a slightly
elongated partially broken CS bond (2.34 Å, Figure 5);
the reaction barrier is only 2.0 kcal/mol. In contrast, the
barrier of sulfoxide rearrangement in MIN20 is higher
(15.8 kcal/mol), and the CS bond distance in TS20-23
is longer (2.52 Å). As found previously,28 the transition
structure of [2,3]-sigmatropic migration in the allyloxy
methyl anion could be located only if Li+ counterion is
involved (from MIN21 via TS21-24); this reaction is 47.8
kcal/mol exothermic and has a barrier 13.1 kcal/mol at
DFT (16.2 kcal/mol at MP2/6-31G28). IRC procedures
applied to these TSs indicated the concerted character
of sigmatropic migrations.
The TS geometries for model [2,3]-sigmatropic migra-
tions are quite different (Figures 2, 3, and 5). The C-C
bond distances in the allylic moieties of TS4-9, TS8-
10, TS11-12, TS13-14, TS15-16, TS17-18, and TS20-
23 are equalized (1.39-1.40 Å), but the values for TS19-
22 and TS21-24 differ considerably. The same differences
have found for the “long“ bonds, which are formed/broken
in the course of the rearrangement.
tures of pericyclic reactions. In these paper, we will
demonstrate that magnetic properties also are helpful in
understanding the nature of the transition structures of
[2,3]-sigmatropic rearrangements. In addition to the
representative examples of ASCs rearrangements, some
typical [2,3]-sigmatropic migrations were computed
(Scheme 10; for optimized geometries see Figure 5) in
order to find out if there are similar trends in the
mechanisms of these transformations.
Despite such pronounced geometrical differences, all
TSs of [2,3]-sigmatropic migrations computed in this
paper have strong cyclic electron delocalization. This
(43) Hammond, G. S. J . Am. Chem. Soc. 1955, 77, 334.

2992 J . Org. Chem., Vol. 65, No. 10, 2000
Fokin et al.
Sch em e 10
studied (Table 3). Thus, the magnetic susceptibility
exaltations (Λ), calculated as a differences in the mag-
netic susceptibilities (ø) of the starting ground states and
corresponding transition states, vary only from -9 to
-15. The negative Λs indicate the aromatic character of
all TSs. The magnitudes agree well with Λ's computed
for five-membered aromatic transition and ground states
with six delocalized electrons. For instance, Λ ) -8.9
previously been computed for the Cs transition structure
of the 1,5-H shift in cyclopentadiene and -17.2 for
-
aromatic cyclopentadienyl anion C5H5 in D5h.44
Recently, NICS21 was shown to be an effective absolute
probe for aromaticity, i.e., requiring no reference com-
pounds or increment schemes. Thus, NICS simply can
be applied for transition states.42f The NICS values,
computed in the geometrical centers of five-membered
rings of all TSs (Table 3), are negative (from -14.8 to
-22.6 at CSGT-B3LYP/6-311+G**//B3LYP/6-31+G*). This
also indicates the strong aromaticity (compare with -12.6
-
computed in the center of the aromatic cyclo-C5H5 in
D5h).44 The NICS values computed with CSGT-B3LYP
method are similar to NICSt computed by IGLO-III/TZ2P.
F igu r e 4. B3LYP/6-31+G* geometries for [2,3]-sigmatropic
We also employed the dissected NICSσ and NICSπ to
characterize the separate contributions of σ- and π-bonds
to the ring currents in TSs.23 Only the contributions from
the five-membered ring bonds are taken into account for
NICSσ and NICSπ (Table 3). The Pipek-Mezey localization
procedure22 gives three “double” bonds (6π-electrons) in
the five-membered rings of TS4-9, TS8-10, TS11-12,
TS13-14, TS15-16, and TS17-18 (Chart 1). The sum
of the π-contributions (NICSπ) from these “double” bonds
to the local shieldings in the centers of these TSs (Table
3) is nearly constant (from -9.0 to -9.9). Both TS4-9Li
and TS8-10Li are strongly polarized by Li+: only one
double bond is localized in the allylic fragment and 4π-
electrons are localized on the CH2dS moiety. Likewise,
6π-electrons are localized for TS20-23 and TS21-24,
but not for the early TS19-22. In the latter, the localiza-
tion procedure shows a 4π + 2σ electron system (Chart
1). Despite the π-contribution decrease in that case
(NICSπ ) -5.2), the NICSt in the center of the TS19-22
still remains highly negative due to the larger σ-contri-
migrations in cyclohexen-1-yl methyl sulfinyl carbanions.
Sch em e 9
could be verified easily from the magnetic properties,44
which are very similar for all transition structures
(44) Schleyer, P. v. R.; J iao, H. Pure Appl. Chem. 1996, 68, 209.

Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2993
F igu r e 5. B3LYP/6-31+G* geometries for ground and transition sates for [2,3]-sigmatropic migrations in allyl methyl sulfur
ylide (MIN19, MIN22, TS19-22), allyl methyl sulfoxide (MIN20, MIN23, TS20-23), and allyloxy methyl lithium (MIN21, MIN24,
TS21-24).
Ch a r t 1
and TS17-18 the synchronicities generally are higher
(from 0.71 to 0.78). The complexation with the Li+ even
increases the synchronicity of the ACS rearrangement:
δBav ) 0.55, Sy ) 0.84 for TS4-9Li and δBav ) 0.52, Sy
) 0.87 for TS8-10Li. This agrees with the increase in
the aromatic manifestation of these TSs relative to free
forms TS4-9 and TS8-10 (see Table 3). In general, the
calculated synchronicities Sy of [2,3]-shifts in allyl sulfinyl
carbanions are similar to those computed for concerted,
synchronous cycloaddition reactions (δBav ) 0.43...48 and
Sy ) 0.7...0.9).18
bution (NICSσ ) -6.5) to the total shielding (Table 3).
Thus, dissected NICSs indicate that both σ- and π-bonds
can contribute to in-plane cyclic ring currents.
Such magnetic properties (in-plane ring currents ef-
fects) of transition structures also give evidence for
concerted reaction mechanisms.45 In addition, we used
bond index criteria to estimate the synchronicity Sy for
[2,3]-sigmatropic reactions.18 Synchronicities were com-
puted (Table 3) for model rearrangements in the sulfur
ylides (TS19-22, Sy ) 0.61), the sulfoxides (TS20-23,
Sy ) 0.57), and for the Wittig rearrangement (TS21-
24, Sy ) 0.59). These Sy values are understandable since
Thus, [2,3]-sigmatropic rearrangements can be classi-
fied as concerted (based on IRC calculations and magnetic
properties of the TSs46) pericyclic reactions with moderate
synchronicity.
Our results indicate that [2,3]-sigmatropic migrations
proceed through strongly cyclic electron delocalized (in-
plane aromatic) transition structures despite varieties in
the charges and the nature of the participating atoms.
Since the geometries of TSs are very different, magnetic
properties (NICS and magnetic susceptibilities) verify the
aromaticity, whereas geometric criteria47 may be mis-
leading if applied to the transition structures.
the TSs are located far from the “halfway” point (δBav
)
0.5) of the reaction. For example, for the early TS19-
22, δBav ) 0.23 and Sy ) 0.61. In contrast, for the late
TS20-23, δBav ) 0.85; the synchronicity also is low (Sy
) 0.57). For the [2,3]-shifts in allyl sulfinyl carbanions
via TS4-9, TS8-10, TS11-12, TS13-14, TS15-16,
(46) Some 1,3-dipolar cycloaddition reactions also proceed via an
aromatic transition structures (see, for example: Morao, I.; Lecea, B.
Coss´ıo, F. P. J . Org. Chem. 1997, 62, 7033).
(47) (a) Katritzky, A. R.; Karelson, M.; Sild, S.; Krygowski, T. M.;
J ug, K. J . Org. Chem. 1998, 63, 5228. (b) Krygowski, T. M.; Cyran˜ski,
M. Adv. Mol. Struct. Res. 1997, 3, 227. (c) Krygowski, T. M.; Cyran˜ski,
M. Tetrahedron 1996, 52, 1713.
(45) (a) Minkin, V. I.; Glukhovtsev, M. N.; Simkin, B. Ya. Aromaticity
and Antiaromaticity. Electronic and Structural Aspects; J ohn Wiley
and Sons: New York, 1994. (b) Dewar, M. J . S. J . Am. Chem. Soc.
1984, 106, 669. (c) Schleyer, P v. R.; J iao, H.; Glukhovtsev, M. N.;
Chandrasekhar, J .; Kraka, E. J . Am. Chem. Soc. 1994, 116, 10129.

2994 J . Org. Chem., Vol. 65, No. 10, 2000
Fokin et al.
Calcd for C10H20S: C, 69.70; H, 11.70; S, 18.60. Found: C,
69.91; H, 11.43; S, 18.26.
Con clu sion s
We have demonstrated that the reaction DMSS with
a number of aliphatic, cyclic, and cage ketones resulted
in the formation of γ-unsaturated thiols. Successive
reactions, i.e., the addition of DMSS to ketone, dehydra-
tion to â-hydroxysulfoxide, [2,3]-sigmatropic rearrange-
ment in allyl sulfinyl carbanion, and reduction of sulfenic
acid derivatives occur as a one-pot process in DMSO. The
best preparative yields (60-75%) were obtained for cyclic
and branched sterically nonhindered ketones.
(2-Meth ylen ecycloh exyl)m eth a n eth iol (13) was pre-
1
pared from cyclohexanone (4) as a colorless oil. H NMR (200
MHz, δ): 1.00-2.90 (12H, m), 4.61 (1H, s), 4.76 (1H, s). 13C
NMR (50.3 MHz, δ): 24.33, 27.28, 28.71, 33.02, 34.87, 46.86,
107.24, 151.03. MS m/z (rel intensity) 142 (21). Anal. Calcd
for C8H14S: C, 67.54; H, 9.92; S, 22.54. Found: C, 67.62; H,
9.81; S, 22.66.
(2-Meth ylen ecycloh ep tyl)m eth a n eth iol (14) was pre-
pared from cycloheptanone (5) as a colorless oil. 1H NMR (200
MHz, δ): 1.20 (8H, m), 2.00-2.50 (6H, m), 4.72 (1H, m), 4.85
(1H, m). 13C NMR (50.3 MHz, δ): 30.84, 31.40, 31.65, 32.23,
33.94, 34.28, 50.08, 114.08, 153.53. MS m/z (rel intensity) 156
(25). Anal. Calcd for C9H16S: C, 69.17; H, 10.32; S, 20.51.
Found: C, 68.74; H, 10.54; S, 20.32.
8-Me t h yle n e -9-m e r ca p t om e t h ylt r icyclo[5.2.1.02,6]-
d eca n e (15) was prepared from tricyclo[5.2.1.02,6]decane-8-
one (6) as a colorless oil. 1H NMR (200 MHz, δ): 0.8-2.8 (16H,
m), 4.63 (1H, s), 4.84 (1H, s). 13C NMR (50.3 MHz, δ): 25.76,
26.68, 27.62, 29.87, 30.32, 42.36, 45.65, 45.79, 48.35, 49.57,
101.58, 156.60. MS m/z (rel intensity) 194 (26). Anal. Calcd
for C12H18S: C, 74.17; H, 9.33; S, 16.50. Found: C, 74.21; H,
9.27; S, 16.32.
3-Ad a m a n ta n -1-yl-bu t-3-en e-1-th iol (16) was prepared
from methyl(1-adamantyl)ketone (7) as a colorless oil. 1H NMR
(200 MHz, δ): 1.60 (12H, m), 2.36 (3H, m), 2.70 (2H, m), 2.95
(3H, m), 3.67 (1H, s), 4.80 (1H, s). 13C NMR (50.3 MHz, δ):
26.76, 28.73, 35.08, 35.30, 37.43, 39.16, 106.12, 155.30. MS
m/z (rel intensity) 222 (17). Anal. Calcd for C14H22S: C, 75.61;
H, 9.97; S, 14.42. Found: C, 75.57; H, 10.11; S, 14.23.
The [2,3]-sigmatropic rearrangements in allyl sulfinyl
carbanions are highly exothermic (from -26 to -29 kcal/
mol at DFT) and the barriers computed for the rear-
rangements in the free anions are low (0.5-3 kcal/mol).
The complexation with the Li+ counterion increases the
barrier of the rearrangement significantly (21-23 kcal/
mol) but does not change the nature of the transition
structures, which bond indexes show to be even more
tightly bound. Alkyl substitution has only a small influ-
ence on the barriers and the geometries of the transition
structures. The [2,3]-sigmatropic migrations in allyl
sulfenyl carbanions are concerted and moderately syn-
chronous (Sy ) 0.7...0.8) processes. Some typical [2,3]-
sigmatropic migrations (in allyl sulfoxides, allyl sulfur
ylides, and Wittig rearrangement) proceed via similar
reaction pathways. Even though the TSs of [2,3]-sigma-
tropic rearrangements formed earlier or later on the
reaction coordinate and are show pronounced bond length
differentiation, all these TSs are aromatic based on their
magnetic properties (NICS and Λ). Localized orbital
calculations show that both σ- and π-bonds are contribute
to the NICS values at the centers of the transition
structures of [2,3]-sigmatropic migrations.
2-Ad a m a n ta n -1-ylm eth yl-p r op -2-en e-1-th iol (17a ) a n d
2-Ad a m a n ta n -1-yl-3-m eth yl-bu t-3-en e-1-th iol (17b). The
mixture of products was prepared from (1-adamantyl)acetone
1
(8) as a colorless oil. H NMR (200 MHz, δ): 1.40-1.87 (17H,
m), 2.35-2.75 (5H, m), 4.66 (1H, m), 4.82 (1H, m). MS m/z
(rel intensity) 236 (17). Anal. Calcd for C15H24S: C, 76.21; H,
10.23; S, 13.56. Found: C, 76.33; H, 10.12; S, 13.51.
4-Meth ylen -5-m er ca p tom eth ylp r otoa d a m a n ta n e (18)
was prepared from protoadamantan-4-one (9) as a colorless
Exp er im en ta l Section
1
oil. H NMR (200 MHz, δ): 1.00-2.20 (16H, m), 4.71 (1H, m),
4.81 (1H, m) 13C NMR (50.3 MHz, δ): 28.25, 28.67, 29.48,
33.68, 33.85, 33.00, 37.88, 40.62, 43.17, 47.86, 108.32, 152.57.
MS m/z (rel intensity) 194 (23). Anal. Calcd for C12H18S: C,
76.21; H, 10.23; S, 13.56. Found: C, 74.33; H, 10.12; S, 13.51.
Gen er a l P r oced u r e for th e P r ep a r a tion of Hom oa llyl-
th iols fr om Keton es. The suspension of NaH (24 mmol) in
dry DMSO (20 mL) under dry argon is stirred at 70 °C until
the hydrogen evolution is completely interrupted, then the
temperature is increased up to 120-130 °C. To the solution
of dimsylsodium thus obtained, the ketone (1-9) (8 mmol) in
5 mL of DMSO was added. The reaction mixture was allowed
to stand at this temperature for 30 min, and then it was cooled,
diluted with 50 mL of cold water, and extracted with dichlo-
romethane (3 × 30 mL). Combined extracts were washed with
water and dried over sodium sulfate and solvent removed in
a vacuum. The residue was purified by column chromatogra-
phy on silica gel (eluant: hexane/ether 5:1). The yields of
corresponding homoallylthiols (10-18) are given in Table 1.
Rea r r a n gem en t of Meth yl (Cycloh exen e-1-yl)m eth yl-
su lfoxid e (B). A. In th e Absen ce of Ba se in DMSO.
Sulfoxide B (158 mg) in 1 mL of DMSO was heated to 130 °C
and allowed to stand for 30 min. The solution was cooled,
diluted with 15 mL of water, and extracted with dichlo-
romethane (3 × 5 mL). Combined extracts were washed with
water, dried over sodium sulfate, and concentrated. The
reaction mixture (130 mg) contained 73% of allylic alcohol C
and 27% of unreacted sulfoxide B from GC/MS data.
B. In th e P r esen ce of DMSS in DMSO. To the solution
of dimsylsodium (146 mg) prepared as described above the
solution of sulfoxide B (316 mg) in 2 mL of dry DMSO was
added. The reaction mixture was allowed to stand for 30 min
at 130 °C, cooled, diluted with 3 mL of water, and extracted
with dichloromethane (3 × 10 mL). Combined extracts are
washed with water, dried over sodium sulfate, and concen-
trated. The reaction mixture (320 mg) contained 81% of thiol
13, 10% of allylic alcohol C, and 9% of unreacted sulfoxide B.
C. In th e P r esen ce of n -Bu Li in Eth er . To the solution
of sulfoxide B (316 mg) in 5 mL of dry ether 2.3 mL of 1.6 M
solution of n-BuLi in ether was added dropwise under stirring
at 0 °C. The reaction was heated to reflux for 2 h, cooled,
quenched with 0.2 g of LiAlH4, diluted with 3 mL of water,
and extracted with ether (3 × 10 mL). Combined extracts were
washed with water, dried over sodium sulfate, and concen-
trated. The residue was purified by column chromatography
on silica gel (eluant: hexane/ether 5:1), and 230 mg (81%) of
thiol 13 was obtained.
2-Eth yl-3-p r op yl-bu t-3-en e-1-th iol (10) was prepared
1
from heptan-4-one (1) as a colorless oil. H NMR (200 MHz,
δ): 0.70-2.60 (16H, m), 4.72 (1H, m), 4.8 (1H, m). 13C NMR
(50.3 MHz, δ): 9.99, 12.26, 19.44, 23.96, 26.48, 34.35, 49.42,
109.09, 149.00. MS m/z (rel intensity) 158 (32). Anal. Calcd
for C9H18S: C, 68.29; H, 11.46; S, 20.25. Found: C, 68.31; H,
11.63; S, 20.01.
3-ter t-Bu tyl-bu t-3-en e-1-th iol (11) was prepared from
1
pinacoline (2) as a colorless oil. H NMR (200 MHz, δ): 1.02
(9H, s), 2.00-2.60 (5H, m), 4.52 (1H, m), 4.80 (1H, m). 13C NMR
(50.3 MHz, δ): 26.30, 27.20, 29.91, 36.12, 106.71, 152.02. MS
m/z (rel intensity) 144 (62). Anal. Calcd for C8H16S: C, 66.60;
H, 11.18; S, 22.22. Found: C, 66.32; H, 10.81; S, 22.43.
3-Hexyl-bu t-3-en e-1-th iol (12a ) a n d 3-Meth yl-2-p en tyl-
bu t-3-en e-1-th iol (12b). The mixture of products was pre-
pared from octan-2-one (3) as a colorless oil. 1H NMR (200
MHz, δ): 1.20-1.50 (11H, m), 1.54 (2H, m), 1.80-3.00 (5H,
m), 4.70-4.83 (2H, m) MS m/z (rel intensity) 172 (28). Anal.

Transformations of Ketones to γ-Unsaturated Thiols
J . Org. Chem., Vol. 65, No. 10, 2000 2995
Ack n ow led gm en t. We gratefully acknowledge the
support of this work by the Fundamental Research
Foundation of the Ukraine and also thank the “Mack-
rochem“ Company for technical support. A.A.F. is grate-
ful to the Alexander von Humboldt Foundation for
support.
J O991672E