Photolysis of Alkyl Aryl Sulfoxides
J . Org. Chem., Vol. 62, No. 4, 1997 863
Melting points were measured by using a Thomas-Hoover
capillary melting point apparatus and are uncorrected. NMR
spectra were obtained on a Varian VXR-300 spectrometer.
Optical rotation was monitored using a DIP-370 Digital
Polarimeter (J apan Spectroscopic Co.) and an Oriel filter (4045
Å, bandwidth 100 Å); precision is (0.001°. GC-MS data were
obtained using a VG Magnum ion trap instrument. Other GC
data were obtained with a HP 5890 Series II gas chromato-
graph equipped with an FID detector and a 10 m HP-1 column.
HPLC data were collected with a HP 1050 liquid chromato-
graph with a diode array detector. An ODS Hypersil reverse
phase column (5 µm, 200 × 2.1 mm) was used. Elutions were
with acetonitrile/water gradients. Response factors were
developed against internal standards for GC and HPLC for
each compound quantified. The estimated error of the re-
sponse factors is about (10%.
Su lfoxid es. (S)-(-)-Methyl tolyl sulfoxide 3 (99%, Aldrich)
was used as received. Diphenyl sulfoxide 11a (Aldrich) was
recrystallized in hexane before use. The preparations of the
aryl benzyl sulfoxides 1, dixylyl sulfoxide 12, and dimesityl
sulfoxide 13 have been described.9,24 Phenyl 2-phenylethyl
sulfoxide 449 was prepared by hydrogen peroxide oxidation of
the corresponding sulfide.50 tert-Butyl phenyl sulfoxide 7 was
prepared in 65% yield from t-butyllithium and (S)-(-)-menthyl
benzenesulfinate.38,51 No attempt was made to assess optical
purity.52
The sulfide was prepared using a slight modification of the
method of Ipatieff.54 2-Methyl-2-phenyl-2-propanol (40 mmol)
and thiophenol (40 mmol) were sequentially added dropwise
to a mixture of 8.3 mL of concentrated sulfuric acid and 4 mL
of water. After 4 h, the mixture was added to a mixture of ice
and ether. After workup and recrystallization from ethanol,
a purified yield of 70% was obtained. 1H NMR (CDCl3) δ 1.20
(s, 6 H), 2.89 (s, 2 H), 7.18 (dd, J ) 7.5 Hz, 1.5 Hz, 2 H), 7.22-
7.42 (m, 6 H), 7.58 (dd, J ) 7.5 Hz, 1.5 Hz, 2 H); 13C NMR
(CDCl3) δ 28.1, 49.0, 49.4, 126.5, 127.9, 128.6, 128.9, 130.8,
132.2, 132.8, 132.9.
1,1-Dim et h yl-3-p h en ylp r op yl P h en yl Su lfoxid e (9).
This compound was prepared in the same fashion as 8 in 93%
yield: mp 68-71 °C; 1H NMR (CDCl3) δ 1.16 (s, 3 H), 1.19 (s,
3 H), 1.74 (ddd, J ) 14.1, 12.3, 5.1 Hz, 1 H), 1.97 (ddd, J )
14.1, 12.3, 5.1 Hz, 1 H), 2.40 (s, 3 H), 2.63-2.82 (m, 2 H), 7.16-
7.49 (m, 9 H); 13C NMR (CDCl3) δ 19.7, 20.1, 21.4, 30.2, 37.6,
58.7, 126.0, 126.4, 128.3, 128.4, 129.1, 136.2, 141.5, 141.6.
The corresponding sulfide was prepared in 82% yield from
p-thiocresol and 2-methyl-4-phenyl-2-butanol as above: 1H
NMR (CDCl3) δ 1.29 (s, 6 H), 1.75 (m, 2 H), 2.34 (s, 3 H), 2.81
(m, 2 H), 7.10-7.30 (m, 5 H), 7.12-7.30 (d, J ) 8.1 Hz, 2H),
7.43 (d, J ) 8.1 Hz, 2 H); 13C NMR (CDCl3) δ 21.2, 28.8, 31.3,
44.1, 48.9, 125.7, 128.3, 128.6, 129.3 (2 overlapping peaks),
137.4, 138.8, 142.5.
1,1-Dim eth ylben zyl p-Tolyl Su lfoxid e (10). This com-
pound was prepared in 87% yield in the same fashion as 8: 1H
NMR (CDCl3) δ 1.47 (s, 3 H), 1.74 (s, 3 H), 2.31(s, 3 H), 6.76
(d, J ) 8.0 Hz, 2 H), 7.01 (d, J ) 8.0 Hz, 2 H), 7.18-7.32 (m,
5 H); 13C NMR (CDCl3) δ 17.9, 21.4, 24.2, 63.0, 125.9, 127.6,
128.0, 128.3, 128.6, 130.9, 138.7, 141.2.
The sulfide was prepared from p-thiocresol and R-methyl-
styrene in the same way as the sulfides of 8 and 9, save that
the alkene was used rather than the alcohol in 44% yield: 1H
NMR (CDCl3) δ 1.68 (s, 6 H), 2.31 (s, 3H), 6.98-7.44 (m, 9 H);
13C NMR (CDCl3) δ 21.2, 29.6, 50.7, 126.4, 126.6, 127.8, 129.0,
136.6, 138.6, 146.5.
Su lfen ic Ester s. Appropriate sulfenic esters were pre-
pared by reaction of alcohols with benzene- or toluenesulfenyl
chloride in the presence of triethylamine.38 After crude
workup, a mixture was obtained that typically contained
starting materials, disulfide, and the sulfenic ester (typically
∼50%) as major components. The sulfenic esters were identi-
fied by its characteristic UV and retention time behavior.
Sufficient purification to get response factors was not generally
achievable, so the response factor developed for benzyl ben-
zenesulfenate9 was used.
Miscella n eou s Com p ou n d s. Phenyl benzenethiosul-
fonate and p-tolyl p-toluenethiosulfonate were prepared by
literature methods.55,56 Phenyl benzenethiosulfinate and p-
tolyl p-toluenethiosulfinate were also prepared by literature
methods.57 The known phenyl 2-phenylethyl disulfide (Ph-
SSCH2CH2Ph) and phenyl 3-phenylpropyl disulfide (PhSSCH2-
CH2CH2Ph) were prepared by the oxidation of equimolar
mixtures of the corresponding thiols.58 The pure compounds
were obtained by silica chromatography of the disulfide
mixtures. 1-Phenyl-2-(phenylthio)ethanol59 and 1-phenyl-3-
(phenylthio)-1-propanol60 were prepared by literature meth-
ods.61 2-Methyl-4-phenyl-2-butene was obtained from ther-
molysis of 9: 1H NMR (CDCl3) δ 1.72 (br s, 3 H), 1.75 (d, J )
1.5 Hz, 3 H), 3.34 (d, J ) 7.2 Hz, 2 H), 5.33 (t of heptets, J )
7.2 Hz, 1.5 Hz, 1 H), 7.15-7.32 (m, 5 H).
Aside from their toxicity, thiophenols, used in the prepara-
tions below, are severe stench hazards. Extreme care should
be exercised that all glassware, gloves, etc., be treated with
bleach prior to cleanup or disposal.
(R)-(+)-P h en yl 3-P h en ylp r op yl Su lfoxid e (5). This
compound was prepared in 40% yield from phenylpropylmag-
nesium bromide and (S)-(-)-menthyl benzenesulfinate.38,51
Repeated recrystallization from benzene-hexane gave a sample
with constant melting point of 53.5-53.8 °C. A racemic
sample had melting point of 44-45 °C: 1H NMR (CDCl3) δ
1.95 (m, 1 H), 2.11 (m, 1 H), 2.65-2.85 (m, 4 H), 7.10-7.32
(m, 5 H), 7.45-7.62 (m, 5 H); 13C NMR (CDCl3) δ 23.6, 34.6,
56.4, 124.1, 126.3, 128.5, 128.6, 129.3, 131.0, 140.5, 143.9;
[R]20
) 0.560 (c 0.119, 2-propanol), [R]20
) 0.623 (c
405nm
405nm
0.120, acetone).
1-Meth yl-2-p h en yleth yl P h en yl Su lfoxid e (6). This
sulfoxide was prepared in 72% yield as a 1.1:1 mixture of two
diastereomers by reaction of Grignard reagent (obtained by
reaction of 2-bromo-1-phenylpropane and magnesium) and (S)-
(-)-menthyl benzenesulfinate in anhydrous ether.38,51 Separa-
tion of this colorless oil on silica gel led to variation of the ratio
of diastereomers, but neither pure diastereomer could be
obtained, so the original mixture was used. Major product:
1H NMR (CDCl3) δ 1.09 (d, J ) 5.1 Hz, 3 H), 2.59 (dd, J )
10.2, 7.9 Hz, 1 H), 2.83-2.99 (m, 1 H), 3.09 (dd, J ) 10.2, 2.7
Hz, 1 H), 7.07-7.68 (m, 10 H). Minor product: 1H NMR
(CDCl3) δ 0.99 (d, J ) 5.1 Hz, 3 H), 2.60 (dd, J ) 10.2, 7.2 Hz,
1 H), 2.83-2.99 (m, 1 H), 3.29 (dd, J ) 10.2, 4.5 Hz, 1 H),
7.07-7.68 (m, 10 H). Mixture: 13C NMR (CDCl3) δ 10.2, 12.7,
34.5, 36.6, 60.8, 60.9, 124.7, 125.1, 126.6, 126.7, 128.5, 128.6,
128.9, 129.0, 129.2 (2 overlapped peaks), 130.8, 131.2, 137.7,
138.1, 141.5, 141.7.
1,1-Dim eth yl-2-p h en yleth yl P h en yl Su lfoxid e (8). This
compound was prepared in quantitative yield by oxidation of
the corresponding sulfide using the H2O2-urea complex:53 mp
1
87-90 °C dec; H NMR (CDCl3) δ 1.05 (s, 3 H), 1.06 (s, 3 H),
2.68 (d, J ) 13.1 Hz, 1 H), 3.01 (d, J ) 13.1 Hz, 1 H), 7.14-
7.32 (m, 5 H), 7.48-7.64 (m, 5 H); 13C NMR (CDCl3) δ 19.3,
20.2, 40.9, 59.4, 126.6, 126.7, 128.1, 128.4, 130.8, 131.2, 135.9,
139.5.
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