Cyclization of 1,3-diaryl-3-phenylsulfanyl-1-propanols to thiochromans with the participation of [1,3]-PhS shift

Article abstract of DOI:10.1016/S0040-4020(03)00519-2

Optically active (3R,1RS)-3-aryl-1-phenyl-3-phenylsulfanyl-1-propanols were easily dehydrated forming mainly rac-cis-2-aryl-4-phenylthiochroman, and rac-cis-4-aryl-2-phenylthiochroman along with the corresponding trans-isomers. The observed reaction outco

Full text of DOI:10.1016/S0040-4020(03)00519-2

Tetrahedron 59 (2003) 3621–3626
Cyclization of 1,3-diaryl-3-phenylsulfanyl-1-propanols to
thiochromans with the participation of [1,3]-PhS shift
a
b
b
Jacek Skarz˙ewski,a Mariola Zielinska-Błajet, Szczepan Roszak and Ilona Turowska-Tyrk
,
*
´
aInstitute of Organic Chemistry, Biochemistry and Biotechnology, Wrocław University of Technology, Wybrzeze S. Wyspianskiego,
50-370 Wrocław, Poland
bInstitute of Physical and Theoretical Chemistry, Wrocław University of Technology, 50-370 Wrocław, Poland
Received 10 December 2002; revised 3 March 2003; accepted 27 March 2003
Abstract—Optically active (3R,1RS)-3-aryl-1-phenyl-3-phenylsulfanyl-1-propanols were easily dehydrated forming mainly rac-cis-2-aryl-
4-phenylthiochroman, and rac-cis-4-aryl-2-phenylthiochroman along with the corresponding trans-isomers. The observed reaction outcome
(rearrangement and racemisation) apparently results from the SEAr reaction involving the unusual 1,3-phenylsulfanyl group migration. This
interpretation is supported by the results of theoretical studies (DFT) on the supposed intermediates. q 2003 Elsevier Science Ltd. All rights
reserved.
1. Introduction
pyran) has been known for its interesting properties, but it
was regarded as an uneasily available one.6 Under these
circumstances and because our cyclization results differed
in some respect from the reported one, we examined this
reaction in more detail, finding that the rare 1,3-shift of
phenylsulfanyl group takes place during the cyclization.
The catalytic enantioselective Michael addition1 of thio-
phenols to chalcones offers an easy access to the respective
optically pure adducts and (þ)-(R)-3-phenylsulfanyl-1,3-
diphenylpropan-1-one, (þ)-1a (over 95% e.e., 70% chem.
yield), an interesting chiral building block is now available
in the multigram quantity.2 In order to elaborate their
synthetic applications we studied possible transformations
of the ketone functionality. Thus, its reduction gave the
corresponding epimeric alcohol (þ)-2a,3 so we attempted
an elimination to get the respective unsaturated enantio-
meric sulfide. Unexpectedly, in both, acid and base-
catalyzed elimination we obtained the cyclized product,
namely 2,4-diphenylthiochroman (3a) (Scheme 1).4
2. Results and discussion
When the racemic alcohol 2a (d.m., 1:1) obtained from the
racemic Michael adduct 1a was heated with solid KHSO4
(20 mol%) in toluene at 808C, water elimination gave
mainly rac-cis-3a (83%) along with rac-trans-3a (7%).
Configuration of the major product (crystalline) was proved
1
undoubtedly by 2D H NMR (NOESY) and single crystal
X-ray study. The presence of the earlier unnoticed5
minor trans-isomer was observed running GC/MS analysis
of the crude product, where two substances of the same
When our work was underway, the similar observation on
the acidic cyclization of rac-2a to 3a was reported.5 The
heterocyclic system of 3 (3,4-dihydro-2H-1-benzothio-
Scheme 1.
Keywords: cyclization; thiochromans; [1,3]-sulfanyl participation; X-ray structures; DFT calculations.
*
Corresponding author. Fax: þ48-71-328-4064; e-mail: skarzewski@kchf.ch.pwr.wroc.pl
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00519-2

3622
J. Skarz˙ewski et al. / Tetrahedron 59 (2003) 3621–3626
Scheme 2.
fragmentation but different retention times were detected.
We were unable to isolate pure trans-3a, however, the
crystallization and the removal of cis-3a led to the sample
enriched in this isomer. Its 1H and 13C NMR spectra
undoubtedly confirmed the structure of the minor isomer.
Generally, a similar result was obtained in the same reaction
with epimeric (þ)-2a. Moreover, the milder elimination,
avoiding acidic conditions (one-pot mesylation in the
presence of excess of triethylamine followed by the
amine-induced elimination of methanesulfonic acid) also
led to a comparable outcome. Thus, (þ)-2a gave mainly cis-
3a (81%) along with trans-3a (17%) (Scheme 2). The direct
cyclization of the benzylic cation formed from the epimeric
alcohol (þ)-2a should produce both cyclized products in the
optically active forms. However, it was not the case. After
recrystallization, we obtained over 57% of the isolated cis-
3a as a racemate. This result suggests that the primarily
formed benzylic carbocation with R-configuration at C-3
undergoes a racemisation, which probably involves a 1,3-
shift of the phenylsulfanyl group. It seems that the
rearranged/racemised cation cyclizes mainly to the most
stable racemic cis-3 with both phenyl groups at the
pseudoequatorial positions (cf. ORTEP drawing, Fig. 1).
On the other hand, the unrearranged cation may also cyclize
and this reaction leaves the stereogenic center intact, so the
formed products should be optically active. The isolated
crystals of cis-3, being essentially racemic, (cf. elementary
cell drawing, Fig. 2.) exhibited small, but measurable
beyond the error, optical rotation (see Section 3). Unfortu-
nately, we were unable to determine the ee of crude cis-3a.
Anyhow, some of this product comes from the unrearranged
cation.
proved by a single crystal X-ray determination (Fig. 3). The
presence of cis-4 and trans-4 resulting from the [1,3]-PhS
shift was recorded as two GC peaks of the same MS
fragmentation. Again, after the removal of the crystalline
1
main isomer, H and 13C NMR of the remaining mixture
allowed for the clear identification of the minor products. As
expected, the ratios of cis/trans for both pairs of products as
Figure 1. An Ortep view of the molecule cis-3a.
In order to verify the hypothetical [1,3]-PhS shift we
obtained (R)-(þ)-3-(4-chlorophenyl)-1-phenyl-3-phenyl-
sulfanylpropan-1-one (1b, 73% e.e.), reduced it to the
corresponding epimeric alcohol (þ)-2b, and submitted that
product to the elimination (MesCl/Et3N). This reaction
delivered all four possible cyclic isomers, again containing
small amounts of the unracemised products (Scheme 3). The
main one was rac-cis-3b, accompanied by rac-trans-3b (the
same MS spectra). The structure of rac-cis-3b was fully
Figure 2. Elementary cell drawing for rac-cis-3a (single crystal X-ray).

J. Skarz˙ewski et al. / Tetrahedron 59 (2003) 3621–3626
3623
Scheme 3.
well as for the pair from the previous reaction are nearly the
same (ca. 7/1).
The second lowest energy trans-sulfonium ion N (8.0 kcal/
mol less than A) leads here to the degenerate rearrangement.
However, in the case of different aryl moieties (as formed
from 2b) this equilibrium should also produce a rearranged
product. Two other cations are the expected Wheland-type
intermediates X and Y (7.2 kcal/mol less than the benzylic
cation A for cis and 6.4 kcal/mol less for trans, respect-
ively), which deprotonate to the corresponding neutral
molecule of cis-3a and trans-3a. These products differ in
energy by 1.8 kcal/mol, while their precursor-intermediates
differ by 0.8 kcal/mol. The observed cis/trans selectivity of
cyclization (7:1, i.e. 87% d.e.) is in a reasonable agreement
with the selectivities resulting from both energy differences
[1,3]-SR Participation of a sulfur atom via a four-membered
sulfonium ion intermediate has already been observed but it
is a rare phenomenon.7 Contrary to the respective [1,2]- and
[1,4]-SPh shifts, which are widely observed,8 four-
membered rings form slowly, the products are significantly
strained and their occurrence requires special facilitating
effects, e.g. the Thorpe–Ingold effect. It seemed that in our
case the presence of 1,3-diaryl substituents could be
responsible for such facilitation. To examine this we
performed theoretical DFT calculations (for the details,
see Section 3) optimizing energy for all of the possible
cationic species formed from (þ)-2a. The obtained results
are presented in Figure 4.
Thus five local energy minimums were found. The highest
energy value corresponds to the open-chain benzylic cation
A and this energy was taken as a reference level. The lowest
energy structure (10.1 kcal/mol less than A) represents the
meso-cis-sulfonium ion M. The observed racemisation can
be accounted for the reversible formation of this species.
Figure 4. The DFT structures of intermediates and products. Relative
energies are given in kcal/mol.
Figure 3. An Ortep view of the molecule rac-cis-3b.

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J. Skarz˙ewski et al. / Tetrahedron 59 (2003) 3621–3626
(95% based on energies of products and 78% based on
energies of intermediates). Also the calculated energy
required for the deprotonation of the Wheland-type
intermediates (ca. 210 kcal/mol) agree with the typical
value of proton affinities.9
and wR2¼0.202 for I.2s(I), R1¼0.088 and wR2¼0.226 for
˚
.
23
all data, S¼1.09, rmax¼0.44, rmin¼20.45 e A
Crystallographic data (excluding structure factors) for the
structures in this paper has been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication numbers CCDC 188981 for 3a and
188982 for 3b. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: þ44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
In conclusion, the results of theoretical studies are in
agreement with the experimental ones and both support the
[1,3]-PhS shift participation in the observed conversion of
1,3-diaryl-3-phenylsulfanyl-1-propanols to thiochromans.
3.3. Preparation of the chiral Michael adducts
3. Experimental
3.1. General
The addition was carried out as reported before.2 The
products were further enantioenriched by recrystallization
from hexane/methylene chloride. For both Michael adducts
the enantiomeric forms were isolated from the mother
liquors and had lower mps than the corresponding racemic
crystals.
Melting points were determined using a Boetius hot-stage
apparatus and are uncorrected. IR spectra were recorded on
a Perkin–Elmer 1600 FTIR spectrophotometer. H NMR
1
and 13C NMR spectra were measured on a Bruker CPX
(300 MHz) spectrometer using TMS as an internal standard.
GC/MS spectra were determined on a Hewlett–Packard
5890 II gas chromatograph (25 m capillary column) with a
Hewlett–Packard mass spectrometer 5971A operating on
the electron impact mode (70 eV). Optical rotations at
578 nm were measured using an Optical Activity Ltd.
Model AA-5 automatic polarimeter. Separations of products
by chromatography were performed on silica gel 60 (230–
400 mesh) purchased from Merck. TLC analyses were
performed using silica gel 60 precoated plates (Merck).
3.3.1. (R)-(1)-1,3-Diphenyl-3-phenylsulfanylpropan-1-
one 1a. Prepared on 10 mmol scale as described earlier,2
70% yield after recrystallization, mp 96–978C;
[a]2D0¼þ136 (1.02, CH2Cl2), .95% e.e. All data are in
agreement with those reported earlier.2
3.3.2. (R)-(1)-3-(4-Chlorophenyl)-1-phenyl-3-phenyl-
sulfanylpropan-1-one 1b. Yield 61%, recrystallized three
1
times, mp 74–758C; H NMR (300 MHz, CDCl3): 3.44–
3.58 (m, 2H, CH2), 4.83 (t, J¼7.1 Hz, 1H, pCH), 7.11–7.25
(m, 9H, ArH), 7.36 (t,† J¼7.5 Hz, 2H, ArH), 7.48 (t,
J¼7.2 Hz, 1H, ArH), 7.79 (d, J¼7.5 Hz, 2H, ArH); IR
(KBr): 3064, 1727, 1687, 1581, 1450, 1224, 1090, 813, 744,
685 cm21; 1H NMR (CCl4, Eu(hfc)3): pCH, Dd 0.123 ppm,
[a]2D0¼þ167 (1.00, CH2Cl2), 73% e.e.
3.2. X-Ray crystallographic data
Colorless crystals of 3a,b suitable for X-ray diffraction
studies were grown by dissolving the compound in ethanol,
and then by the slow evaporation at room temperature. The
crystals were examined on
diffractometer equipped with
˚
a
Kuma KM4CCD
a CCD camera
3.4. Preparation of the alcohols
(l¼0.71073 A, umax¼268) at 293(2) K. Precise shell con-
stants were determined by the least-squares method on the
ground of the most of the data collection reflections. The
data were corrected for the Lorentz-polarization effect.10
The structures were solved by direct methods from
SHELXS-9711 and refined by SHELXL-97.12 All non-
hydrogen atoms were treated anisotropically. Hydrogen
atoms were found from a DF map and refined without
constraints.
The reduction with LAH was carried out as described
before.3
3.4.1. (3R)-1,3-Diphenyl-3-phenylsulfanylpropan-1-ol
2a. Diastereomeric ratio 50:50. Yield 98%. All spectral
data were reported in the literature.3
1
rac-2a. Yield 100%. H NMR (300 MHz, CDCl3): 1.88 (s,
1H,OH), 2.16–2.25 and 2.27–2.41 (two m, 2H, CH2), 4.18
and 4.35 (t, J¼7.4 Hz, dd, J1¼9.7 Hz, J2¼5.7 Hz, 1H, S–
CH), 4.48 and 4.82 (dd, J1¼9.4 Hz, J2¼3.8 Hz, dd,
J1¼7.9 Hz, J2¼5.7 Hz, 1H, CH), 7.10–7.30 (m, 15H,
ArH); IR and MS spectra are in agreement with the
literature data.5
3.2.1. Compound 3a. Monoclinic, C2/c, a¼22.203(2),
˚
b¼8.3995(5), c¼19.9649(19) A, b¼121.179(13)8, Dx¼
3
1.261 mg m23
,
V¼3185.5(5) A , Z¼8, m¼0.20 mm21
,
˚
F(000)¼1280, CCD camera, 8925 reflections collected,
3134 unique reflections, 2778 observed unique reflections,
Rint¼0.031, R1¼0.060 and wR2¼0.163 for I.2s(I),
R1¼0.066 and wR2¼0.168 for all data, S¼1.08,
3.4.2. (3R)-3-(4-Chlorophenyl)-1-phenyl-3-phenyl-
sulfanylpropan-1-ol 2b. Diastereomeric ratio 50:50.
23
˚
rmax¼0.27, rmin¼20.27 e A
.
1
Yield 95%. H NMR (300 MHz, CDCl3): 1.80 (br s,1H,
OH), 2.22–2.36 and 2.39–2.50 (two m, 2H, CH2), 4.23 and
4.38 (dd, J1¼8.1 Hz, J2¼6.7 Hz, dd, J1¼9.8 Hz, J2¼5.6 Hz,
1H, S–CH), 4.51 and 4.91 (dd, J1¼9.6 Hz, J2¼3.8 Hz, dd,
3.2.2. Compound 3b. Triclinic, P11, a¼8.4836(9), b¼
˚
9.9211(13), c¼11.1661(13) A, a¼68.686(12), b¼
80.763(9), g¼83.817(10)8, Dx¼1.296 mg m23
,
V¼
3
862.93(18) A , Z¼2, m¼0.339 mm21, F(000)¼352, CCD
camera, 4614 reflections collected, 3109 unique reflections,
2270 observed unique reflections, Rint¼0.062, R1¼0.070
˚
†
The reported J values are those observed from the splitting patterns in the
spectrum and may not reflect true coupling constant values.

J. Skarz˙ewski et al. / Tetrahedron 59 (2003) 3621–3626
3625
J1¼7.9 Hz, J2¼5.6 Hz, 1H, CH), 7.11 (d, J¼8.4 Hz, 1H.
NMR (75 MHz): 42.1 (C-3), 44.8 (C-2), 50.4 (C-4), 124.1,
125.8, 126.5, 127.1, 127.2, 127.8, 128.7, 7, 131.4, 134.4,
135.1, 140.3, 144.9 (aromatic moiety). GC retention time:
20.4 min (from 140 to 2908C, 88C/min); MS (EI, 70 eV):m/z
(%)¼302 (87) [Mþ], 211 (65), 210 (93), 197 (100), 165
(37), 91 (17), 77 (12), 51 (8).
ArH), 7.17–7.38 (m, 13H, ArH); IR (film): 3396, 3061,
1584, 1490, 1438, 1091, 1056, 1025, 827, 751, 701 cm21
;
MS (EI, 70 eV): m/z (%)¼354 (1) [Mþ], 244 (15), 110 (51),
107 (100), 79 (46), 77 (32), 65 (8), 51 (9); [a]2D0¼þ144
(1.02, CH2Cl2); Rf¼0.35 (tert-BuOMe/CHCl3/hexane,
2.0:2.0:12.0).
3.6.3. 2-(4-Chlorophenyl)-4-phenylthiochroman cis-3b.
Yield 72%. Mp 146.5–1478C (EtOH); 1H NMR (300 MHz,
CDCl3): 2.47–2.58 (m, 2H, CH2), 4.24 (dd, J1¼10.9 Hz,
J2¼5.1 Hz, 1H, CH), 4.60 (dd, J1¼11.0 Hz, J2¼3.5 Hz, 1H,
S–CH), 6.72 (d, J¼8.0 Hz, 1H, ArH), 6.90 (t, J¼7.4 Hz,
1H, ArH), 7.07 (t, J¼7.5 Hz, 1H, ArH), 7.14 (d, J¼7.6 Hz,
1H, ArH), 7.18–7.42 (m, 9H, ArH); 13C NMR (75 MHz):
41.5 (C-3), 45.4 (C-2), 47.6 (C-4), 124.4, 126.1, 126.7,
126.9, 128.7, 128.8, 128.9, 129.0, 130.1, 133.5, 134.2,
136.8, 139.8, 144.8 (aromatic moiety); IR (KBr): 3060,
3027, 1586, 1490, 1453, 1434, 1089, 1014, 833, 749,
701 cm21. GC retention time: 23.1 min (from 150 to 2908C,
7.58C/min); MS (EI, 70 eV): m/z (%)¼336 (35) [Mþ], 244
(20), 211 (54), 210 (74), 197 (100), 165 (33), 152 (13), 125
(10), 91 (12), 77 (15), 51 (9); [a]2D0¼23.0 (0.98, CH2Cl2).
Anal. calcd for C21H17ClS (336.88): C, 74.87; H, 5.09; Cl,
10.52; S, 9.52. Found: C, 74.59; H, 5.41; Cl, 10.86; S, 9.09.
3.5. Cyclization under acidic conditions
A solution of alcohol 2a (0.285 g, 0.89 mmol) in dry toluene
(30 mL) with a catalytic amount of KHSO4 (0.024 g,
20 mol%) was placed in a rotatory evaporator equipped
with a catch-drop. This mixture was heated at 75–808C
under slightly reduced pressure for 1.5 h, until a half amount
of toluene was distilling off. The reaction color turned from
light-yellow to brown during that time. Next the reaction
mixture was allowed to cool to room temperature, KHSO4
was filtered off, and then the solvent was evaporated under
the reduced pressure. The crude product was purified by
crystallization from hexane/methylene chloride. The
1
analysis of both, the crystals and filtrate by H NMR and
GC/MS indicated that thiochroman 3a was obtained in a
crude yield of 90% and that it contained a mixture of two
diastereomers: cis-3a (83% yield) and trans-3a (7% yield).
1
3.6.4. trans-3b. Yield 11%. H NMR (300 MHz, CDCl3):
3.6. Cyclization under basic conditions
2.43–2.58 (m, 2H, CH2), 4.17 (dd, J1¼10.1 Hz, J2¼4.7 Hz,
1H, CH), 4.39 (dd, J1¼9.1 Hz, J2¼4.2 Hz, 1H, S–CH),
6.70–7.42 (m, 13H, ArH); 13C NMR (75 MHz): 42.0 (C-3),
44.7 (C-2), 49.9 (C-4), 125.7, 126.5, 127.2, 127.4, 127.8,
128.6, 128.7, 128.8, 129.8, 131.3, 134.0, 134.7, 139.1, 144.7
(aromatic moiety). GC retention time: 21.2 min (from 150
to 2908C, 7.58C/min); MS (EI, 70 eV):m/z (%)¼336 (48)
[Mþ], 244 (21), 211 (53), 210 (76), 197 (100), 165 (32), 152
(11), 125 (10), 91 (11), 77 (16), 51 (10).
Freshly distilled methanesulfonyl chloride (0.151 mL,
1.95 mmol) was added dropwise to a magnetically stirred
solution of the appropriate alcohol 2 (1.5 mmol) and Et3N
(1.672 mL, 12 mmol) in dry toluene (10 mL) cooled to
2108C. This mixture was stirred for 0.5 h at this
temperature and then kept overnight at 2208C. Finally,
the reaction mixture was slowly warmed to 508C. After
cooling to room temperature the reaction mixture was
quenched with 1N HCl, and extracted with Et2O
(2£10 mL). The combined extracts were washed with
satd. aq. NaHCO3, water and brine before drying with
Na2SO4 and concentrating in vacuo. The crude product was
purified by column chromatography on silica gel using as
eluent tert-BuOMe/CHCl3/hexane (2.5:2.0:10 for 3a and
2.5:2.0:14 for 3b and 4).
3.6.5. 2-Phenyl-4-(4-chlorophenyl)thiochroman cis-4.
1
Yield 15%. H NMR (300 MHz, CDCl3): 2.27–2.31 (m,
2H, CH2), 3.97 (dd, J1¼9.3 Hz, J2¼5.9 Hz, 1H, CH), 4.21–
4.27 (m, 1H, S–CH), 6.73–7.44 (m, 13H, ArH); 13C NMR
(75 MHz): 41.6 (C-3), 46.0 (C-2), 47.2 (C-4), 124.3, 126.3,
126.8, 127.6, 127.9, 128.7, 128.9, 129.0, 129.9, 132.5,
134.7, 136.2, 141.0, 143.6 (aromatic moiety); this spectrum
was subtracted from that of the mixture with 3b, see above.
GC retention time: 33.1 min (from 150 to 2908C, 7.58C/
min); MS (EI, 70 eV): m/z (%)¼336 (5) [Mþ], 235 (17), 233
(39), 199 (100), 165 (11), 151 (8), 135 (10), 115 (17), 109
(23), 91 (21), 77 (8), 65 (10), 51 (4).
3.6.1. 2,4-Diphenylthiochroman cis-3a. Yield 81%. Mp
1
129.5–1308C (hexane, CH2Cl2), lit.5 mp 129–1328C; H
NMR (300 MHz, CDCl3): 2.45–2.54 (m, 2H, CH2), 4.19
(dd, J1¼10.4 Hz, J2¼6.1 Hz, 1H, CH), 4.57 (dd,
J1¼10.4 Hz, J2¼4.4 Hz, 1H, S–CH), 6.66 (d, J¼7.8 Hz,
1H, ArH), 6.83 (t, J¼7.5 Hz, 1H, ArH), 7.00 (t, J¼7.5 Hz,
1H, ArH), 7.08 (d, J¼7.9 Hz, 1H, ArH), 7.15–7.37 (m,
10H, ArH); 13C NMR (75 MHz): 41.6 (C-3), 46.1 (C-2),
47.8 (C-4), 124.2, 126.1, 126.6, 126.8, 127.6, 127.8, 128.7,
130.0, 134.7, 136.8, 141.2, 145.0 (aromatic moiety); IR
(KBr): 3057, 2913, 1601, 1585, 1492, 1452, 1051, 763,
700 cm21. GC retention time: 20.7 min (from 140 to 2908C,
88C/min); MS (EI, 70 eV): m/z (%)¼302 (88) [Mþ], 211
(66), 210 (95), 197 (100), 165 (33), 91 (18), 77 (12), 51 (7);
[a]2D0¼22.0 (1.52, CH2Cl2).
3.6.6. trans-4. Yield 2%. GC retention time: 32.1 min (from
150 to 2908C, 7.58C/min); MS (EI, 70 eV): m/z (%)¼336 (3)
[Mþ], 235 (16), 233 (41), 199 (100), 165 (17), 151 (3), 135
(6), 115 (22), 109 (21), 91 (16), 77 (13), 65 (15), 51 (7).
3.7. Details of the theoretical treatment
The theoretical studies supporting the search for the reaction
mechanism were performed applying the density functional
theory (DFT) method. The DFT approach utilized Backe’s
three-parameter functional13 with the local correlation part
of Vosco et al.14 and the non-local part of Lee et al.15
(abbreviated as B3LYP). The calculation were performed in
the standard 6-13Gp atomic basis set.16 The enthalpy
1
3.6.2. trans-3a. Yield 17%. H NMR (300 MHz, CDCl3):
2.31–2.41 (m, 2H, CH2), 3.95 (t, J¼7.6 Hz, 1H, CH), 4.34
(t, J¼3.9 Hz, 1H, S–CH), 6.66–7.36 (m, 14H, ArH); 13C

3626
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5. Jensen, A. W.; Manczuk, J.; Nelson, D.; Caswell, O.; Fleming,
S. A. J. Heterocycl. Chem. 2000, 37, 1527–1531.
6. Ingall, A. H. Comprehensive Heterocyclic Chemistry;
Katritzky, A. R., Ed.; Pergamon: Oxford, 1984; Vol. 3,
pp 885–942.
differences between studied moieties taking part in the
proposed reaction scheme were calculated for the theoreti-
cally optimized structures. The results reported here were
obtained using the GAUSSIAN-98 code.17
Additional information including MS fragmentation
schemes for 3a,b, and 4 as well as the Cartesian coordinates
for the optimized structures (Fig. 4) are available from the
corresponding author upon request.
7. Eliel, E. L.; Pearson, W. H.; Jewell, L. M.; Abatjoglou, A. C.;
Kenan, W. R. Tetrahedron Lett. 1980, 31, 331–334, and
references cited therein.
8. For a recent review, see: Fox, D. J.; House, D.; Warren, S.
Angew. Chem. Int. Ed. 2002, 41, 2462–2482.
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This work was supported by grants from Wrocław
University of Technology and in part by grant 7 T09A
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