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A solution of methoxymethyl trimethylsilane
(400 µL, 2.57 mmol) in CCl4 (5 mL), was treated
dropwise with a solution of bromine (132 µL, 2.57 mmol)
in CCl4 (4 mL). The mixture was stirred until it became
colorless. A solution of dithiol 1 (315 µL,
2.57 mmol) in CH2Cl2 (5 mL) was then added
and the mixture was stirred overnight. After washing with water,
the organic layer was dried (Na2SO4). Eva-poration
of the solvent gave 525 mg (2.55 mmol) of crude product 3 (99%), which was purified by
chromatography on silica gel (hexanes/EtOAc 200:1), to
afford the pure isomers 3a and 3b. 3a: 1H
NMR(ppm): δ = 0.14 (s, 9 H), 1.25-1.28 (m,
6 H), 3.50-3.64 (m, 2 H), 3.69 (s, 1 H). 13C
NMR(ppm): δ = -2.5, 16.5, 36.9, 53.2.
MS: m/z (%) = 206
(5) [M+], 150 (11), 135 (32),
73 (100), 59 (16), 55 (11). Calcd for C8H18S2Si:
C, 46.54; H, 8.79. Found: C, 46.20; H, 8.90. 3b: 1H
NMR(ppm): δ = 0.16 (s, 9 H), 1.31 (d, 6 H, J = 6.6 Hz), 3.62-3.75
(m, 2 H), 3.81 (s, 1 H). 13C NMR(ppm): δ = -2.6, 15.5,
33.7, 53.4. MS: m/z (%) = 206
(30) [M+], 163 (25), 150 (71),
135 (100), 73 (89), 59 (56). Calcd for C8H18S2Si:
C, 46.54; H, 8.79. Found: C, 46.32; H, 9.06.
<A NAME="RG14802ST-9">9</A>
Typical Procedure
: A solution of 2-trimethylsilyl-4,5-dimethyl-1,3-dithiolane 3a (134 mg, 0.65 mmol), and benzaldehyde
(132 µL, 1.3 mmol) in anhyd DMF (3 mL) was stirred for
30 min on activated molecular sieves 4 Å, then CsF (99
mg 0.65 mmol) was added and stirred at r.t. overnight. Then, the
solution was extracted with diethyl ether, washed with water, dried
(Na2SO4) and evaporated. TLC of the crude
mixture (8:1 hexane/EtOAc) gave 90 mg (0.37 mmol, 57%)
of 4a. 1H NMR(ppm): δ = 1.32-1.39
(m, 6 H), 2.85 (bs, 1 H), 3.62-3.84 (m, 2 H), 4.73 (dd,
1 H, J = 7.0
Hz, 1.6 Hz), 4.86 (d, 1 H, J = 7.0 Hz),
7.32-7.44 (m, 5 H). 13C NMR(ppm): δ = 16.6,
17.1, 52.4, 53.5, 60.7, 77.3, 126.4, 128.3, 128.4, 141.2. MS: m/z (%) = 240
(0.08) [M+], 222 (5), 166
(5), 135 (15), 134 (34), 133 (100), 121 (6), 107 (8), 89 (11), 77
(25), 59 (16), 55 (22). Calcd for C12H16OS2: C,
59.96; H, 6.71. Found: C, 59.57; H, 6.75. Following the same procedure,
starting from 100 mg (0.48 mmol) of 3b were
obtained 62 mg (0.26 mmol, 54%) of 4b. 1H NMR(ppm): δ = 1.29
(d, 3 H, J = 6.6
Hz), 1.31 (d, 3 H, J = 6.6
Hz), 3.67-3.86 (m, 2 H), 4.64 (d, 1 H, J = 7.0
Hz), 4.73 (d, 1 H, J = 7.0
Hz), 7.28-7.44 (m, 5 H). 13C NMR(ppm): δ = 15.8,
16.5, 52.1, 52.7, 59.4, 77.4, 126.8, 128.2, 128.3, 140.6. MS: m/z (%) = 222
(21) [M+ - 18), 166 (16),
134 (100), 121 (22), 107 (35), 105 (23), 91 (24), 89 (33), 79 (67),
77 (96), 59 (40), 55 (31). Calcd for C12H16OS2: C,
59.96; H, 6.71. Found: C, 59.72; H, 6.93.
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<A NAME="RG14802ST-22">22</A>
meso-4,6-Dimethyl-1,3-dithiane 10 (57 mg, 0.39 mmol) dissolved under an
inert atmosphere in anhyd THF was cooled to -78 °C
and treated with butyllithium (244 µL,
1.6 M solution,
0.39 mmol), stirred 2 h, then cannulated into a -78 °C
cooled solution of Me3SiCl (51 mg, 0.46 mL, 0.47 mmol)
and stirred for an additional hour. After warming to
-20 °C,
the solution was diluted with ether and a solution of NH4Cl,
the organic layer separated and evaporated to afford 73 mg of crude
product 11a (85%). 1H
NMR(ppm): δ = 0.18 (s, 9 H), 1.22 (d, 6 H, J = 6.6 Hz),
1.15-1.25 (m, 1 H, partially overlapped with the peak at
1.22 ppm), 2.09 (dt,
1 H, J = 13.6
Hz, J = 2.4
Hz), 2.69-2.86 (m, 2 H), 3.64 (s,
1 H). 13C
NMR(ppm): δ = -2.5, 22.3, 36.3, 40.9,
44.6. MS: m/z (%) = 220
(7) [M
+
],
147 (8), 115 (100), 73 (52), 69 (10), 59 (13). Calcd for C9H20S2Si:
C, 49.03; H, 9.14. Found: C, 48.80; H, 9.00.
<A NAME="RG14802ST-23">23</A>
11b: Yield
69%. 1H NMR(ppm): δ = 0.17
(s, 9 H), 1.23 (d,
6 H, J = 7.0
Hz), 1.20-1.36 (m, 1 H), 1.96-2.09 (m, 1 H), 2.79-2.99
(m, 2 H), 3.20 (s, 1 H). 13C NMR(ppm): δ = -1.1, 23.1,
28.8, 36.2, 42.7. MS: m/z (%) = 220
(6) [M
+
],
147 (11), 115 (100), 73 (77), 69 (13), 59 (19). Calcd for C8H18S2Si:
C, 46.54; H, 8.79. Found: C, 48.85; H, 9.08.
<A NAME="RG14802ST-24">24</A>
12a: Yield
72%. 1H NMR(ppm): δ = 1.23
(d, 3 H, J = 7.0 Hz),
1.26 (d, 3 H, J = 6.6
Hz), 1.27-1.34 (m, 1 H, partially overlapped with the peak
at 1.26 ppm), 2.07 (dt, 1 H, J = 13.8
Hz, J = 2.4
Hz), 2.74-2.94 (m, 2 H), 4.49 (d, 1 H, J = 6.2
Hz), 4.93 (d, 1 H, J = 6.2
Hz), 7.31-7.52 (m, 5 H). 13C
NMR(ppm): δ = 21.6, 21.7, 39.7, 40.1, 43.9, 57.3,
76.0, 126.4 128.3, 128.4, 140.1. MS: m/z (%) = 254
(1) [M
+
],
199 (2), 147 (100), 105 (6), 91 (13), 77 (15), 69 (23). Calcd for C13H18OS2:
C, 61.37; H, 7.13. Found: C, 61.05; H, 7.20.
<A NAME="RG14802ST-25">25</A>
12b: Yield
63%. 1H NMR(ppm): δ = 1.18
(d, 3 H, J = 7.0 Hz),
1.26 (d, 3 H, J = 6.6
Hz), 1.25-1.43 (m, 1 H), 2.12 (dtd, 1 H, J = 13.6
Hz, J = 2.6
Hz, J = 1.2
Hz), 3.00-3.19 (m, 2 H), 3.75 (d, 1 H, J = 9.8
Hz), 4.80 (d, 1 H, J = 9.8
Hz), 7.31-7.44 (m, 5 H). 13C
NMR(ppm): δ = 21.7, 33.7, 34.3, 43.5, 53.0, 73.8,
127.3, 128.1, 128.2, 140.7. MS: m/z (%) = 254 (0.04) [M
+
], 236 (1), 147
(100), 134 (5), 105 (11), 77 (21, 69 (36), 59 (15). Calcd for C13H18OS2:
C, 61.37; H, 7.13. Found: C, 61.00; H, 7.34.