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Appl. Chem. Vol. 74, No. 8, pp.
Pure and Applied
Vol. 74, Issue 8
Alkaloid synthesis via [3+2] cycloadditions*
William H. Pearson
Department of Chemistry, University of Michigan, Ann
Arbor, MI, 48109-1055, USA
Abstract: Tin-lithium exchange on (2-azaallyl)stannanes
affords nonstabilized 2-azaallyllithiums (2-azaallyl anions) that undergo
with alkenes to afford pyrrolidines. The scope of this method has been
expanded to include 2-azapentadienyllithiums and heteroatom-substituted
2-azaallyllithiums. Alternatively, the (2-azaallyl)stannanes may also
be used to generate nonstabilized azomethine ylides via N-alkylation/destannylation
or N-protonation/destannylation, and these ylides were also
found to be useful for the synthesis of pyrrolidines by [p4s+p2s]
cycloadditions with alkenes. Applications of both methods to the total
synthesis of alkaloids such as (+)-coccinine, lepadiformine stereoisomers,
lapidilectine B, and indolizidine 239CD have been accomplished.
* Plenary lecture presented at the 3rd Florida Conference
on Heterocyclic Chemistry (FloHet-III), Gainesville, Florida, USA, 6-8
March 2002. Other lectures are published in this
issue, pp. 1317–1368.
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