GOLDEN OPPORTUNITIES IN THE SYNTHESIS OF NATURAL PRODUCTS AND BIOLOGICALLY ACTIVE COMPOUNDS - Modern Tools for the Synthesis of Complex Bioactive Molecules - page 127

AuCl 3
(5 mol%)
CH 2 Cl 2 /CH 3 CN
CaCO 3 , rt, 1 h
76%

NHBoc

O

O NBoc

n -Pr

n -Pr

105 106

( cis / trans = 4:1)

9 steps

O O

H

H H

N

N

n -Pr

n -Pr O O O

107

Porantheridine 108

SCHEME 4.31 Synthesis of porantheridine by Bates and Lu.

[Au]

HO

AuCl (5 mol%)
AgOTf (15 mol%)
Toluene, 110°C, 6 h
69%

NHTs n -Pr NH

Ts

n -Pr

109

1. Pd/C, MeOH
2. Mg, MeOH

3. MeI, K 2 CO 3 , THF
90%

N n -Pr N

Ts

n -Pr

(±)-Angustureine 111 110

SCHEME 4.32 Synthesis of ( )-angustureine by Chan and coworkers.

4.3.1.2. From Alkynes Alkynes can also undergo gold-catalyzed additions
of a nitrogen nucleophile. This transformation can lead to the formation of endo-
or exocyclic enamine derivatives of types (Scheme 4.33). When the

nucleophile is a primary amine, the enamines can tautomerize to the corresponding
imines depending on the substrate and the reaction conditions used.
In an early report on gold catalysis, Fukuda and Utimoto showed that the
reaction of 5-hexynylamine derivatives

112 and 113

114 and 117 with 5 mol% of sodium

G

endo

G = H

N N

G

NH

R R

Au(I) or Au(III)

112

R

G

exo G = H

N N

G = H, alkyl, aryl,
COR, CO 2 R, SO 2 R

R R

113
SCHEME 4.33