REARRANGEMENTS IN NATURAL PRODUCT SYNTHESIS - Modern Tools for the Synthesis of Complex Bioactive Molecules - page 259

HO

n -BuLi, Et 2 O
5 min at -78°C
and 1 h at 0°C

OH O

O

O

TBS

O

92%

O O O O

(+)-Xestoquinone

SCHEME 8.29 [1,2]-Wittig rearrangement as a key step in the synthesis of

( þ )-xestoquinone.

KH, 18-crown-6
THF, 0°C to rt, 3 h

O SnBu 3

OH

n -SnBu 3 SnCH 2 I

86%

TESO

TESO

H

H

TBSO

TBSO

-BuLi, Hexane
-50°C to 0°C, 5 h

n

78%

O O

OH

OMe

TESO

H

O

H

(-)-Candelalide A TBSO

SCHEME 8.30 [2,3]-Wittig rearrangement as akeystep in the synthesis of ( )-candelalideA.

the voltage-gated potassium channel Kv1.3, is based on the [2,3]-Wittig rearrange-
ment shown in Scheme 8.30 [154] using the Still variant [150].
An asymmetric [2,3]-Wittig rearrangement on a dienolate of a chiral
b -pyrrolidinyl- g -allyloxyl- a , b -unsaturated ester using (1 S ,2 R ,4 R )-2-hydroxy-7,7-
dimethylbicyclo[2.2.1]heptane-1-carboxylic acid diisopropylamide as chiral
auxiliary has been applied successfully to prepare a key intermediate in a synthesis
of (

þ )-eldanolide [155] (Scheme 8.31).

OR*

O

CON( -Pr) 2

OH

i Xylene

reflux , 3 h
94%

CON( i -Pr) 2

O

O

O

+

N

H

H

O

O

O

O

O

O

LDA
THF/ Hexane
-78°C, 6 h
90%

O

O

CON( i -Pr) 2

N

R* =

H

(ee = 93%)

(+)-Eldanolide

SCHEME 8.31 [2,3]-Wittig rearrangement for ( þ )-eldanolide.