1,4-Silatropy of S-R-Silylbenzyl Thioesters
S-r-Tr im eth ylsilylben zyl 2-(4-Ch lor op yr id in e)ca r bo-
128.2, 128.3, 128.7, 137.0, 140.3, 140.9, 148.4, 188.6; MS (EI)
m/z (rel intensity) 371 (M+, 27), 356 (20), 249 (25), 195 (100),
73 (99); HRMS (EI) calcd for C19H21NO3SSi (M+) 371.1011,
found 371.1010. Anal. Calcd for C19H21NO3SSi: C, 61.42; H,
5.70; N, 3.77; S, 8.63. Found: C, 61.13; H, 5.60; N, 3.77; S,
8.51.
th ioa te (3f). A colorless oil (65 mg, 21%): IR (KBr) 1668 cm-1
;
1H NMR (CDCl3) δ 0.10 (s, 9H), 4.17 (s, 1H), 7.09-7.16 (m,
1H), 7.21-7.31 (m, 4H), 7.48 (dd, 1H, J ) 5.1, 2.0 Hz), 7.89
(d, 1H, J ) 2.0 Hz), 8.59 (d, 1H, J ) 5.1 Hz); 13C NMR (CDCl3)
δ -2.5, 35.4, 120.9, 125.4, 127.4, 127.7, 127.9, 141.0, 145.5,
149.7, 152.9, 191.6. MS (EI) m/z (rel intensity) 337 (M+ + 2,
15), 335 (M+, 35), 320 (27), 195 (100), 185 (23), 73 (70); HRMS
(EI) calcd for C16H18ClNOSSi (M+) 335.0566, found 335.0564.
S-r-Tr im eth ylsilylben zyl Th ioa ceta te (3g). A colorless
oil (1.69 g, 67%): IR (neat) 1692 cm-1; 1H NMR (CDCl3) δ 0.04
(s, 9H), 2.30 (s, 3H), 4.03 (s, 1H), 7.10-7.28 (m, 5H); 13C NMR
(CDCl3) δ -2.4, 30.2, 36.0, 125.6, 127.8, 128.2, 141.4, 195.2;
MS (EI) m/z (rel intensity) 238 (M+, 47), 223, (20), 195 (100),
73 (68); HRMS (EI) calcd for C12H18OSSi (M+) 238.0848, found
238.0842.
S-r-Tr im eth ylsilylben zyl (E)-4-Meth oxyth iocin n a m a te
(6c). A bright yellow solid (815 mg, 88%): mp 107.5-108.5
1
°C; IR (KBr) 1653 cm-1; H NMR (CDCl3) δ 0.07 (s, 9H), 3.83
(s, 3H), 4.19 (s, 1H), 6.59 (d, 1H, J ) 15.8 Hz), 6.89 (br d, 2H,
J ) 8.9 Hz), 7.13 (m, 1H), 7.21-7.30 (m, 4H), 7.46 (br d, 2H,
J ) 8.9 Hz), 7.54 (d, 1H, J ) 15.8 Hz); 13C NMR (CDCl3) δ
-2.4, 35.7, 55.4, 114.3, 122.3, 125.4, 126.8, 127.8, 128.1, 130.0,
140.1, 141.5, 161.4, 189.0; MS (EI) m/z (rel intensity) 356 (M+,
19), 341 (5), 281 (3), 195 (10), 161 (100), 133 (13), 73 (23);
HRMS (EI) calcd for
C
20H24O2SSi (M+) 356.1266, found
356.1263. Anal. Calcd for C20H24O2SSi: C, 67.37; H, 6.78; S,
8.99. Found: C, 67.40; H, 6.82; S, 8.91.
S-r-(Dim et h ylp h en ylsilyl)b en zyl Th iob en zoa t e (3h ).
A white solid (6.10 g, 81%): mp 84.0-85.0 °C; IR (KBr) 1660
cm-1
;
1H NMR (CDCl3) δ 0.35 (s, 3H), 0.39 (s, 3H), 4.43 (s,
S-r-Tr im eth ylsilylben zyl (E)-Th iocr oton a te (6d ). A
1H), 7.06-7.21 (m, 5H), 7.28-7.44 (m, 7H), 7.52 (m, 1H), 7.92
(br d, 2H, J ) 7.3 Hz); 13C NMR (CDCl3) δ -4.1, -3.7, 35.2,
125.6, 127.2, 127.6, 127.9, 128.1, 128.4, 129.5, 133.1, 134.2,
135.4, 136.7, 140.7, 191.0; MS (EI) m/z (rel intensity) 362 (M+,
26), 347 (5), 285 (9), 257 (66), 135 (100), 105 (23). Anal. Calcd
for C22H22OSSi: C, 72.88; H, 6.12; S, 8.84. Found: C, 73.06;
H, 6.17; S, 8.83.
colorless oil (209 mg, 78%): IR (neat) 1674 cm-1 1H NMR
;
(CDCl3) δ 0.05 (s, 9H), 1.85 (dd, 3H, J ) 1.6, 7.0 Hz), 4.11 (s,
1H), 6.13 (dq, 1H, J ) 1.6, 15.4 Hz), 6.88 (dq, 1H, J ) 7.0,
15.4 Hz), 7.12 (m, 1H), 7.14-7.27 (m, 4H); 13C NMR (CDCl3)
δ -2.5, 18.1, 35.3, 125.4, 127.7, 128.0, 129.7, 140.6, 141.4,
189.1; MS (EI) m/z (rel intensity) 264 (M+, 2), 249 (23), 195
(42), 73 (100), 69 (74); HRMS (EI) calcd for C14H20OSSi (M+)
264.1004, found 264.1005.
S-r,r-Bis(t r im et h ylsilyl)b en zyl Th iob en zoa t e (3i).
DMAP (10 mol %) was used as a catalyst. A white solid (420
S-r-Tr im et h ylsilylb en zyl Th iom et h a cr yla t e (6e). A
colorless oil (200 mg, 74%): IR (neat) 1666 cm-1 1H NMR
;
mg, 92%): mp 94.0-96.5 °C; IR (KBr) 1666 cm-1 1H NMR
;
(CDCl3) δ 0.05 (s, 9H), 1.94 (d, 3H, J ) 1.4 Hz), 4.05 (s, 1H),
5.56 (q, 1H, J ) 1.4 Hz), 6.10 (s, 1H), 7.12 (m, 1H), 7.19-7.25
(m, 4H); 13C NMR (CDCl3) δ -2.4, 18.3, 35.5, 123.0, 125.4,
127.8, 128.0, 141.4, 143.5, 192.7; MS (EI) m/z (rel intensity)
264 (M+, 12), 249 (5), 195 (57), 73 (100), 69 (43); HRMS (EI)
calcd for C14H20OSSi (M+) 264.1004, found 264.0997.
(CDCl3) δ 0.24 (s, 18H), 7.09 (m, 1H), 7.20-7.33 (m, 4H), 7.44
(m, 2H), 7.56 (m, 1H), 8.01 (br d, 2H, J ) 7.0 Hz); 13C NMR
(CDCl3) δ 1.4, 37.2, 124.4, 127.2, 127.3, 127.5, 128.4, 132.9,
137.4, 139.8, 191.7; MS (EI) m/z (rel intensity) 372 (M+, 100),
357 (36), 299 (10), 267 (68), 225 (13), 179 (19), 163 (29), 135
(27), 105 (37), 73 (63); HRMS (EI) calcd for C20H28OSSi2 (M+)
372.1399, found 372.1398.
S-r,r-Bis(tr im eth ylsilyl)ben zyl (E)-Th iocin n am ate (6f).
A bright yellow solid (540 mg, 68%): mp 61.0-62.5 °C; IR
S-r,r-Bis(tr im eth ylsilyl)m eth yl Th ioben zoa te (3j). A
(KBr) 1657 cm-1 1H NMR (CDCl3) δ 0.11 (s, 18H), 2.30 (s,
;
colorless oil (400 mg, 54%); IR (neat) 1659 cm-1 1H NMR
;
1H), 6.76 (d, 1H, J ) 15.5 Hz), 7.38 (m, 3H), 7.54 (m, 2H),
7.60 (d, 1H, J ) 15.5 Hz); 13C NMR (CDCl3) δ -0.3, 14.1, 124.5,
128.2, 128.8, 130.2, 134.2, 139.1, 189.9; MS (EI) m/z (rel
intensity) 322 (M+, 25), 307 (54), 249 (11), 163 (30), 131 (100),
103 (29), 73 (53); HRMS (EI) calcd for C16H26OSSi2 (M+)
322.1243, found 322.1248. Anal. Calcd for C16H26OSSi2: C,
59.57; H, 8.12; S, 9.94. Found: C, 59.37; H, 7.95; S, 9.90.
Th er m a l 1,4-Sila tr op ic Rea ction s of Th ioester s 3a -f
a n d 6a -f. S-R-Trimethylsilylbenzyl thioester 3 or 6 (0.05
mmol) and mesitylene (4.5 µmol) in benzene-d6 (0.5 mL) were
heated in a sealed NMR tube at 180 °C until the disappearance
of the starting material. The reaction was monitored by 1H
NMR. The yields of (E)- and (Z)-silyl enol and dienol ethers (4
and 7) and thiophenes (8), presented in Tables 1 and 2, were
determined by comparison of diagnostic vinyl proton signals
(CDCl3) δ 0.11 (s, 18H), 2.37 (s, 1H), 7.44 (m, 2H), 7.56 (m,
1H), 8.00 (br d, 2H, J ) 7.02 Hz); 13C NMR (CDCl3) δ -0.3,
13.8, 127.0, 128.4, 132.8, 137.1, 192.2; MS (EI) m/z (rel
intensity) 296 (M+, 39), 281 (59), 191 (27), 163 (78), 149 (30),
105 (100), 73 (88); HRMS (EI) calcd for C14H24OSSi2 (M+)
296.1086, found 296.1077.
Gen er a l P r oced u r e for th e P r ep a r a tion of Th ioester s
6a -f. DCC (580 mg, 2.81 mmol) was added to a mixture of
R-silylmethylthiol (2.55 mmol), R,â-unsaturated carboxylic acid
(2.71 mmol), and DMAP (20 mg, 0.16 mmol) in CH2Cl2 (50 mL)
at 0 °C, and the reaction mixture was stirred at the same
temperature for 2 h and then at room temperature for 1 h.
The precipitated dicyclohexylurea was removed by filtration.
The filtrate was washed with 0.5 N HCl, a saturated NaHCO3
solution, and brine, dried over MgSO4, and concentrated in
vacuo. The residue was purified by column chromatography
on silica gel to give thioester 6.
1
on H NMR of the crude reaction mixture, based on the added
mesitylene as an internal standard. The reaction mixture was
concentrated in vacuo and separated by column chromatog-
raphy on silica gel.23 Silyl enol ethers 4a ,24 4c,25 4g,24,26 and
4h 27 are known compounds.
S-r-Tr im eth ylsilylben zyl (E)-Th iocin n a m a te (6a ). A
white solid (732 mg, 88%): mp 46.5-47.5 °C; IR (KBr) 1672
cm-1 1H NMR (CDCl3) δ 0.08 (s, 9H), 4.20 (s, 1H), 6.71 (d,
;
1-(4-Nit r op h en yl)-1-t r im et h ylsiloxy-2-p h en ylet h en e
(4b). Key spectra of 4b obtained from the crude product
mixture (Z/E 91:9): 1H NMR (C6D6) δ 0.07 (s, 8.2H), 0.11 (s,
0.8H), 6.10 (s, 0.9H), 6.23 (s, 0.1H), 7.00-8.00 (m, 9H). Z-4b:
13C NMR (C6D6) δ 0.70, 114.1, 123.6, 126.3, 127.4, 128.6, 129.4,
1H, J ) 15.7 Hz), 7.15 (m, 1H), 7.24-7.31 (m, 4H), 7.37-7.42
(m, 3H), 7.53 (m, 2H), 7.58 (d, 1H, J ) 15.7 Hz); 13C NMR
(CDCl3) δ -2.4, 35.8, 124.6, 125.5, 127.8, 128.1, 128.2, 128.8,
130.4, 134.1, 140.3, 141.3, 189.1; MS (EI) m/z (rel intensity)
326 (M+, 27), 311 (16), 195 (100), 131 (51), 103 (20), 73 (72);
HRMS (EI) calcd for C19H22OSSi (M+) 326.1161, found 326.1176.
Anal. Calcd for
Found: C, 69.96; H, 6.73; S, 9.85.
C19H22OSSi: C, 69.89; H, 6.79; S, 9.82.
(23) Attempts to separate the isomeric products by distillation or
GPC were unsuccessful.
(24) Davis, F.; Sheppard. A. C.; Chen, B.-C.; Haque, M. S. J . Am.
Chem. Soc. 1990, 112, 6679.
(25) Davis, B. R.; Hinds, M. G. Aust. J . Chem. 1997, 50, 309.
(26) Fleming, I.; Roberts, R. S.; Smith, S. C. J . Chem. Soc., Perkin.
Trans. 1 1998, 1215.
(27) Loeschorn, C. A.; Nakajima, M.; McCloskey, P. J .; Anselme, J .-
P. J . Org. Chem. 1983, 48, 4407.
S-r-Tr im eth ylsilylben zyl (E)-4-Nitr oth iocin n am ate (6b).
A yellow solid (320 mg, 33%): mp 125.5-127.0 °C; IR (KBr)
1
1657 cm-1; H NMR (CDCl3) δ 0.09 (s, 9H), 4.21 (s, 1H), 6.79
(d, 1H, J ) 15.9 Hz), 7.15 (m, 1H), 7.21-7.30 (m, 4H), 7.54 (d,
1H, J ) 15.9 Hz), 7.65 (br d, 2H, J ) 8.9 Hz), 8.24 (br d, 2H,
J ) 8.9 Hz); 13C NMR (CDCl3) δ -2.5, 36.2, 124.1, 125.7, 127.7,
J . Org. Chem, Vol. 68, No. 16, 2003 6169