10686
K. L. Stensaas et al. / Tetrahedron 62 (2006) 10683–10687
3. Conclusions
peroxide (1.127 g, 0.0374 mol) by literature procedures15
in methanol (39.76 mL) with a formic acid catalyst
(0.994 mL). The reaction mixture was extracted with
50 mL of distilled water and 35 mL fractions of ethyl ether,
and the organic layer was dried with MgSO4. Compound 3
was recrystallized with petroleum ether. Lit. mp: 75–
Several interesting conclusions can be drawn from this work:
(1) The singlet oxygen mode selectivity for vinyl sulfides
are susceptible to a combination of factors including
the solvent, reaction temperature, and the electronic
character of the p-substituent. In particular, hydrogen
bonding stabilization of the perepoxide by a protic sol-
vent favors formation of the dioxetane.
(2) The overall trend for geminal selectivity in allyl sulfides,
sulfoxides, and sulfones increases with increasing size
of the allyl substituent; allyl sulfide 2b produced 52%,
allyl sulfoxide 4b produced 75%, and allyl sulfone 7b
produced 83% of the ene hydroperoxide resulting from
geminal hydrogen abstraction.
1
76.5 ꢀC, H NMR (CDCl3) d 1.6 (s, 3H), 1.8 (s, 3H), 2.2
(s, 3H), 7.2–7.5 (m, 5H).
4.1.3. 2-Methyl-3-phenylsulfonyl-2-butene (6). It was syn-
thesized by the oxidation of 1a (1 g, 0.0056 mol) with
2.5 molar equiv of meta-chloroperoxybenzoic acid (2.42 g,
0.014 mol). Compound 1a was dissolved in dichloromethane
with 1 equiv of sodium bicarbonate. m-CPBA was dissolved
in dichloromethane in an addition funnel and added dropwise
to the sulfide solution for 15 min. The solution was then
stirred and cooled over ice for an additional 45 min. The
product was washed with 2ꢁ20 mL portions of distilled
water, 3ꢁ20 mL portions of 2 M NaOH, and 20 mL portions
of distilled water. The organic layer was dried over MgSO4
and purified on a silica gel column using 7:3 hexane/ethyl
acetate 1H NMR (CDCl3) d 1.93 (s, 3H), 2.08 (s, 3H), 2.28
(s, 3H), 7.4–8.0 (m, 5H).
(3) Vinyl sulfoxides and sulfones show no solvent effects,
which is unexpected when compared to their solvent
dependent a,b-unsaturated ester and acid counterparts.
4. Experimental
4.1. General
4.1.4. 1-Bromo-2,3-dimethyl-2-butene. It was prepared
using literature procedures14 by the reaction of 2,3-dimethyl-
2-butene (40.4 mmol) and N-bromosuccinimide (41.1 mmol)
in a solution of carbon tetrachloride (25 mL) with benzoyl
peroxide (0.129 mol). The product mixture was distilled
under reduced pressure at 65 ꢀC (24 mm Hg). 1H NMR
(CDCl3) d 1.7 (s, 3H), 1.77 (s, 6H), 4.08 (s, 2H).
1H NMR spectra were recorded on a 60 MHz Varian EM
360-L spectrometer and referenced internally to tetramethyl-
silane. Melting points were taken in open capillaries on
a Mel-Temp II apparatus and are uncorrected. Thin layer
chromatography was carried out on 250 mm layer silica gel
flexible plates and column chromatography was carried
out with SilicAR CC-4 silica gel obtained from Mallinck-
rodt. Methyl isopropyl ketone and thiophenol were obtained
from Eastman and used as received. Anhydrous HCl,
m-chloroperoxybenzoic acid, 2,3-dimethyl-2-butene, N-bro-
mosuccinimide, benzoyl peroxide, and p-nitrothiophenol
were purchased from Aldrich and used without further puri-
fication. Hydrogen peroxide (30%) and dichloromethane
were obtained from Fisher and used as received. Sodium
methoxide from Mallinckrodt and formic acid from JT
Baker were also used without further purification. Deuter-
ated solvents (benzene, methanol, chloroform, acetonitrile,
and deuterium oxide) and photosensitizers (rose bengal,
methylene blue, and tetraphenylporphine) were used as
received.
4.1.5. 1-[(4-Nitrophenyl)thio]-2,3-dimethyl-2-butene
(2c). It was synthesized from the reaction6 of 1-bromo-2,3-
dimethyl-2-butene (1.0 g, 6.13 mmol) with p-nitrothiophe-
nol (1.18 g, 6.20 mmol) in a solution of absolute ethanol
(45 mL) and sodium methoxide (0.335 g, 6.22 mmol). The
product was extracted using diethyl ether and water, dried
with MgSO4, and purified through recrystallization from
hexanes. Mp: 67–69 ꢀC (lit. mp: 67–68 ꢀC), 1H NMR
(CD3OD) d 1.65–2.0 (m, 9H), 3.85 (s, 2H), 7.6 (d, 2H,
J¼9 Hz), 8.3 (d, 2H, J¼9 Hz).
4.1.6. 1-[(4-Nitrophenyl)sulfonyl]-2,3-dimethyl-2-butene
(7c). Compound 2c (0.217 mmol) was oxidized with 2 equiv
of m-chloroperoxybenzoic acid (0.434 mmol) in a solution
of dichloromethane (5 mL) as per literature procedure.14
The m-CPBA was extracted using saturated NaHCO3, the
products were washed with ether and a saturated NaCl solu-
tion, and dried with MgSO4 before undergoing reduced pres-
4.1.1. 2-Methyl-3-phenylthio-2-butene (1a). It was synthe-
sized according to literature procedures15 from the reaction
of methyl isopropyl ketone (6.55 g, 0.076 mol) and thiophe-
nol (6.06 g, 0.055 mol). After the reaction was cooled to
0 ꢀC, anhydrous HCl was bubbled through the system as
thiophenol (10.69 g, 0.097 mol) was added from an addition
funnel dropwise for 40 min. After the solution warmed to
room temperature, the excess ketone was distilled off at at-
mospheric pressure (bp 94–95 ꢀC). The crude product then
underwent reduced pressure distillation to yield 6 mL of dis-
tillate; this was then dissolved in ether, extracted with 2 M
NaOH to remove excess thiophenol, and dried with NaSO4.
1
sure distillation to remove the solvent. H NMR (CD3OD)
d 1.2–1.65 (m, 9H), 3.9 (s, 2H), 8.05 (d, 2H, J¼6 Hz),
8.35 (d, 2H, J¼6 Hz).
4.2. Singlet oxygen photooxidation procedure for 1a
Samples of 1a (0.5 M) immersed in an ice bath were photo-
oxidized in benzene-d6 using 2ꢁ10ꢂ4 M tetraphenylpor-
phine (TPP) as the photosensitizer and a sodium nitrite
filter solution (75 g NaNO2/100 mL H2O). After 4 h of
photooxidation, all the starting material reacted to form either
1act [1H NMR (C6D6) d 1.63 (s, 3H), 1.77 (s, 3H), 5.35 (s,
1H, J¼8 Hz), 5.47 (s, 1H, J¼8 Hz), 6.92–7.57 (m, 5H)] or
1
Lit. bp: 49.5–50 ꢀC (0.03 mm Hg), H NMR (C6D6): d 1.6
(s, 3H), 1.95 (s, 3H), 2.01 (s, 3H), 7.05–7.35 (m, 5H).
4.1.2. 2-Methyl-3-phenylsulfinyl-2-butene (3). Compound
1a (1.77 g, 0.0099 mol) was oxidized with 30% hydrogen