Chemistry Reference
In-Depth Information
OTHP
O
OTHP
O
1. piperidine
THPO
OH
176
2.
DBU (
1
)
THPO
OH
OHC
toluene
N
O
N
O
177
89%
(2 steps)
Me
Me
OTHP
O
O
O
Me
O
O
Me
THPO
O
O
O
N
Me
N
O
Me
O
178
Sch 57050 (
179
)
(estrogen antagonist)
Scheme 7.39
Synthesis of estrogen antagonist Sch 57 050 (179)
)-dolabellatrienone (56) [13], in which
spontaneous cyclization of 192 occurred via the acid chloride to give a mixture of 193 and
194. This mixture was subsequently converted to 56 exclusively by treatment with DBU
(Scheme 7.44).
The cyathane diterpenoids have a characteristic 5-6-7 membered tricyclic skeleton. Piers
et al. reported the synthesis of one of the cyathane diterpenoids, (
)-sarcodonin G (198)
[58]. In this synthesis, a mixture of 196 and 197 (30 : 1) obtained from selenide 195 by
oxidation, cleanly isomerized to give thermodynamically favoured 197 in the reaction with
DBN in refluxing benzene (Scheme 7.45).
Similar conditions, that is, DBU in benzene at 75
C, were effectively applied to the
synthesis of scabronine G 201 by Waters et al. [59] (Scheme 7.46).
Corey et al. reported the reaction of singlet oxygen with conjugated diene 203, which was
obtained from the isomerization reaction of
Corey and Kania reported a synthesis of (
þ
-unsaturated lactone 202 using a catalytic
amount of DBN. The resulting peroxide intermediate 204 was converted to (
a
,
b
)-folskolin
(205) [60] (Scheme 7.47).
Renneberg et al. reported a synthesis of (
þ
)-coraxeniolide A (208) [61]. In this synthesis,
isomerization at the
-position (C4) was achieved by the use of TBD. Thus, alkylation of
206 at C4 was conducted with LDA and 1-bromo-4-methylpent-2-ene to give a mixture of
coraxeniolide A (208) and its C4 epimer 207 in a ratio of 1 : 5.7 (Scheme 7.48). TBD
treatment of the mixture caused epimerization at C4, changing the product ratio to 3 : 1.
An isomerization reaction at an
a
-position with superbase was also applied in the
synthesis of taxol (157) by Kusama et al. [48]. C10
a
a
-Acetate 210, obtained from the enol
