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H
CO
2
Me
C
12
H
25
TBDPSO
O
O
O
34
OMOM
OBOM
35
OMOM
H
TBDPSO
SO
2
Ph
TBDPSO
O
O
36
37
OMO
O
C
12
H
25
OTBDPS
O
OMOM
OBOM
SO
2
Ph
38
OTHP
OMOM
OMOM
CH
O
C
12
H
25
CO
2
Me
O
OMOM
OBOM
39
OH
OH
O
C
12
H
25
15
20
O
10
4
O
OH
OH
pseudo annonacin A
threo-trans-erythro
Scheme 10-10. Total synthesis of pseudo-annonacin A by Hanessian and Grillo.
route was significantly improved. The Wittig reaction of aldehyde 29 with ylide
derived from compound 30, and followed by two steps of transformations, provided
epoxide 32. The following epoxide-opening reaction of 32 by terminal alkyne
14 afforded the desired linear skeleton. The aldol-based protocol elaborated
the lactone moiety on this intermediate, and annonacin was given after final
deprotections.
31,33
Hanessian and Grillo tried to identify the stereochemistries of the THF region of
annonacin A by the total synthesis. Unfortunately, they only obtained pseudoan-
nonacin A, a diastereomeric isomer of annonacin A (Scheme 10-10).
36
The key
THF-containing segment 35 and sulfone 37 were prepared from L- and D-glutamic
acid-derived chirons, respectively. Treatment of sulfone 37 with n-BuLi and then
condensation with ester 35 afforded 38. Reductive removal of sulfone followed
by reduction of ketone functionality and two-carbon extension at the right side
gave skeleton intermediate 39. The lactone unit of target was introduced by the
aldol strategy. Final deprotections gave a mixture of epimers at C-10, pseudoanno-
nacin A. The relative configuration of the THF region of pseudoannonacin A is
threo-trans-erythro (from left to right in Scheme 10-9).
A series of chiral stannic synthons was developed and applied successfully into
the synthesis of acetogenins by Marshall Jiang. In the synthesis of longifolicin
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