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C. K. Jin et al.
LETTER
MHz, CDCl3): = 194.8, 170.6, 155.7, 136.2, 128.5, 128.2,
128.1, 67.1, 53.6, 52.8, 31.2, 30.4; MS (EI): m/z = 311 [M+],
208(10) [M – 103]+, 91(100) [M – 220]+. Data for 15: IR
(KBr): 3040, 2990, 2950, 1720 cm–1; 1H NMR (500 MHz,
CDCl3): = –0.28 (s, 3 H), –0.22 (s, 3 H), 0.01 (s, 6 H), 0.57
(s, 9 H), 0.71 (s, 9 H), 1.95 (s, 1 H), 2.14 (s, 1 H), 3.79 (s, 1
H), 3.90 (d, 1 H, J = 14.7), 4.06 (s, 1 H), 5.14 (s, 1 H), 5.42
(d, 1 H, J = 14.8), 7.03–7.08 (m, aromatic 4 H); 13C NMR
(125 MHz, CDCl3): = 202.4, 194.2, 134.9, 128.9, 128.5,
128.2, 86.2, 79.6, 72.4, 48.8, 30.9, 26.1, 25.9, 18.5, 18.2,
–3.7, –4.6, –4.8; MS (EI): m/z = 525 [M+], 468(100) [M –
C(CH3)3]+, 392(27) [M – 133]+. Data for 16: IR (KBr): 3010,
2950, 2850, 1700 cm–1; 1H NMR (500 MHz, CDCl3):
= 0.04 (s, 9 H), 0.24 (s, 9 H), 2.34 (s, 3 H), 4.02 (t, 1 H,
J = 1.57), 4.24 (d, 1 H, J = 14.9), 4.31 (d, 1 H, J = 1.8), 5.25
(s, 1 H), 5.29 (d, 1 H, J = 1.4), 5.54 (d, 1 H, J = 15.3), 7.03–
7.08 (m, aromatic 4 H); 13C NMR (125 MHz, CDCl3):
= 201.9, 193.1, 134.1, 128.0, 127.6, 127.3, 84.9, 78.7,
70.9, 48.2, 30.0, –0.5, –0.7; MS (EI) m/z = 441 [M+], 426(30)
[M – CH3]+, 350(25) [M – 91]+, 91(97) [M – 350], 73(100)
[M – 368]. Data for 23: IR (KBr): 3320, 3040, 2950, 2790,
1730 cm–1; 1H NMR (500 MHz, CDCl3): = 1.40 (t, 1 H,
J = 8.9), 2.97–2.98 (m, 1 H), 3.76 (s, 3 H), 4.65–4.67 (m, 1
H), 5.12 (s, 2 H), 5.74 (d, 1 H, J = 5.7), 7.25–7.35 (m,
aromatic 5 H); 13C NMR (125 MHz, CDCl3): = 170.5,
157.5, 136.0, 128.5, 128.3, 128.1, 67.2, 55.3, 52.7, 27.1; MS
(EI): m/z = 269 [M+], 208(40) [M – 61]+, 91(100) [M –
178]+. Data for 24: IR (KBr): 3030, 2950, 2850, 2560, 1460
cm–1; 1H NMR (500 MHz, CDCl3): = 0.11 (s, 3 H), 0.63 (s,
3 H), 0.19 (s, 6 H), 0.73 (s, 9 H), 0.86 (s, 9 H), 2.57 (d, 1 H,
J = 11.4), 4.13 (s, 1 H), 4.17 (d, 1 H, J = 14.4), 4.18 (s, 1 H),
4.32 (d, 1 H, J = 15.1), 5.83 (d, 1 H, J = 15.1), 7.18–7.23 (m,
aromatic 4 H); 13C NMR (125 MHz, CDCl3): = 200.6,
134.3, 128.8, 128.5, 128.0, 127.9, 86.6, 80.0, 69.6, 47.8,
25.9, 25.8, 25.5, 18.1, 17.8, –4.0, –4.9, –5.0; MS (EI) m/z =
483 [M+], 426(100) [M – C(CH3)3]+, 392(27) [M – 91]+,
91(66) [M – 392]+. Data for 25: IR (KBr): 3030, 2950, 2850,
2550, 1470 cm–1; 1H NMR (500 MHz, CDCl3): = 0.08 (s,
9 H), 0.23 (s, 9 H), 2.47 (d, 1 H, J = 11.0), 4.12 (t, 1 H,
J = 2.5), 4.24 (dd, 1 H, J = 2.4, J = 11.0), 4.26 (d, 1 H,
J = 2.5), 4.34 (d, 1 H, J = 15.0), 5.90 (d, 1 H, J = 15.0), 7.19–
7.33 (m, aromatic 4 H); 13C NMR (125 MHz, CDCl3):
= 201.1, 134.3, 128.7, 128.2, 128.0, 127.9, 85.7, 81.4,
78.5, 68.2, 47.9, 0.8, 0.5, 0.4, 0.01, 0.01; MS (EI) m/z =
399.7 [M+], 366(56) [M – SH]+, 217(48) [M – 182]+, 73(100)
[M – 326]+.
In summary, a new chemoselective method for deprotec-
tion of thioesters has been developed. The process, which
employs TiCl4/Zn in CH2Cl2, is particularly applicable to
deprotection reactions of substrates that contain acid, base
or LiAlH4 sensitive functionality. Further studies, probing
the mechanism, scope and possible limitations of this
methodology are in progress.
Acknowledgement
Financial support for this work was provided by a grant from the
Brain Korea 21 Project(1999), Korea Research Foundation, Korea.
References
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151(16) [M – PhCO]+, 105(100) [M – 105]. Data for 14: IR
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3.75 (s, 3 H), 4.58–4.59 (m, 1 H), 5.11 (s, 2 H), 5.51–5.5 (d,
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Synlett 2001, No. 12, 1956–1958 ISSN 0936-5214 © Thieme Stuttgart · New York