GOLDEN OPPORTUNITIES IN THE SYNTHESIS OF NATURAL PRODUCTS AND BIOLOGICALLY ACTIVE COMPOUNDS - Modern Tools for the Synthesis of Complex Bioactive Molecules - page 124

OMOM MOMO AuL OMOM

(JohnPhos)AuNTf 2
(3 mol%)

O

O n -Bu

O O

O n -Bu (3 equiv)
CH 2 Cl 2 , rt, 2 h

O n -Bu

R

R R

89a 90 91a

R = H
89b

(R = H, 82 %)
91b R = Me (R = Me, 94%)

H H

OH NMe 2

O O

Me H

NMe 2 . HCl

92 93

SCHEME 4.26

C-C bonds has been recently described by Liu and coworkers [23]. These authors
have reported that the treatment of alkynes 89a and 89b with a catalytic amount of
gold catalyst [(JohnPhos)AuNTf 2 ] in the presence of n -butyl vinyl ether allows the
formation of the new oxabicyclononadiene structures

91a and 91b by a formal [4+2]-

cycloaddition proceeding on an s - trans -oxonium of type (Scheme 4.26). This

gold-catalyzed transformation might be useful to synthesize the bioactive molecules
92

90

and 93 , which exhibit NCS activity and HIV-1 inhibitory effects.

4.3. GOLD-CATALYZED FORMATION
OF NITROGEN-CONTAINING HETEROCYCLES

Analogously to the formation of oxygen-containing heterocycles, nitrogen-contain-
ing heterocycles can be produced by the addition of a nitrogen nucleophilic species on
an alkyne or an allene-ene possessing. They can be alternatively obtained by the
cycloisomerization of an enyne or an allene-ene possessing a nitrogen atom in their
linker (formation of a new C-C bond). These transformations have been mainly
employed for the synthesis of alkaloids possessing a structural unit derived from a
pyrrolidine, a piperidine, a pyrrole, or a pyridine (Scheme 4.27).

C-N bond formation C-C bond formation

n n

HN HN

G

G

m N

G

n

N
G

N N

G

N

N

G G

N
G

N
G

N
G

n

N
G

N
G

N

G

SCHEME 4.27