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OH
OAc
OAc
OAc
O
Steps
a
b
c
OH
O
OH
O
+
OTBS
O
OTBS
OH
91
130
123
131
132
OAc
OH
O
g
e
f
d
O
O
O
O
O
O
HO
O
14
14
14
OH
O
O
O
O
133
134
135
136
±
5
Reagents and Conditions: (a) LDA,
78
C, 1 h, 84%; (b) TBAF, THF, 25
C, 0.5 h; (c) Me
2
C(OMe)
2
,
p-TsOH, DMF, 0.5 h; (d) K
2
CO
3
, MeOH, 2.5 h; (e) MnO
2
,Et
2
O, 4 h; (f) TiCl
4
/Zn, THF, reflux, Py, 20 h,
58%; (g) 1N HCl-MeOH, 30
C, 0.5 h, 64%.
Scheme 6-6
in 13.7% overall yield by means of an intramolecular nucleophilic addition of
sulfur-stabilized carbanion to ketone as key steps (Scheme 6-8).
86
6.4.2
Total Synthesis of Cembrene A and C
(R)-Cembrene A (59), isolated from termite, some plants, and soft coral succes-
sively, has been shown to be a highly active scent-trail pheromone.
87-90
Cembrene
OH
Cl
OH
steps
a
b
O
O
O
O
137
138
139
SPh
SPh
SPh
c
d
e
O
O
O
OH
140
141
142
OH
17
Reagents and Conditions: (a) CCl
4
, PPh
3
,reflux, 78%; (b) PhSNa, MeOH, 80%; (c) p-TsOH, acetone,
98%; (d) LDA, THF,
78
C, 58%; (e) Li-Et-NH
2
,
78
C, 78%.
±
Scheme 6-7
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