Download (3249Kb) - D-Scholarship@Pitt - University of Pittsburgh

Scheme 3.19 Tandem cycloadditions of [4]-dendralene reported by Willis.
130
Me
N
O O
excess
THF, rt
MeN
O
MeN
O
MeN
H
H
O
O
O
H
H
H
131 (21%)
O
H
132
133
O
H
H
NMe
O
MeN
O
MeN
O
H
H
O
H
H
O
H
H H
O
N
O
Me
134 (4%)
H H
H H
O
H
O
N
O
Me
H
NMe
O
MeN
O
H
O
H
H
H H
O
N
O
Me
MeN
O
135 (42%)
H
O
H
H H
H H
O
H
O
N
O
Me
136 (14%) 137 (14%)
It was reasoned that the cyclic trienes obtained via an allenic Alder-ene reaction (Table 3.1)
could offer a solution to the regioselectivity issues in these tandem cycloaddition reactions by
locking one diene in an unreactive s-trans conformation. We were interested in exploring the
feasibility of both cycloaddition pathways illustrated in Scheme 3.20. Pathway A involves
sequential intermolecular cycloaddition reactions of triene 111 using two different dienophiles
(111→138→139). Alternatively, pathway B, involves an intra-/intermolecular cycloaddition
sequence (111→140→141→142).
47
H
NMe
O