GOLDEN OPPORTUNITIES IN THE SYNTHESIS OF NATURAL PRODUCTS AND BIOLOGICALLY ACTIVE COMPOUNDS - Modern Tools for the Synthesis of Complex Bioactive Molecules - page 142

O

O

R R

O O O R

O R

[Au] Nu

O O

and/or

Nu Nu

1 3

1 3

[Au] -

[Au]

-

[Au]

[Au]

211 212

OTBS

1. [(JohnPhos)Au(NCCH 3 )] + SbF 6 - (2 mol%)

TBSO TBSO

CH 2 Cl 2 , 0°C, 2 h
2. K 2 CO 3 , MeOH

AuL

OAc AcO

AcO 90%

213 214

TBSO TBSO

H

TBSO H H

H

H

H H

steps

AuL

OAc OAc

H
Capnellene 216

H

O

215

SCHEME 4.62 Synthesis of capnellene by Malacria and coworkers.

initially produced allene , which then entered into a cascade comprising a Nazarov-

type reaction and an electrophilic cyclopropanation to furnish the tetracyclic com-
pound

214

. This example highlights the potential of gold catalysis to generate
molecular complexity since three new C-C bonds were created in a single operation
and in an efficient and stereoselective manner.
A 3,3-rearrangement of a propargylic ester was also used by Gung and co-
workers in their approach to the synthesis of the antiangiogenesis natural product
cortistatin A

215

219 (Scheme 4.63) [62]. The A-D ring system of the targeted molecule

OAc

N
Au O

O

AcO

AcO

Cl

(5 mol%)

Cl

D

B

O

O

A

NaHCO 3 (1 equiv)

O

C

CH 2 Cl 2 , rt, 48 h

217 218

3 steps

OH

N

HO

N

D

D

B
C

B
C

O

A

O A

E

H

Me 2 N

Cortistatin A 219

SCHEME 4.63 Synthesis of cortistatin by Gung and coworkers.