Novel cyclization and reductive coupling of bicyclic olefins with
alkyl propiolates catalyzed by nickel complexes*
Dinesh Kumar Rayabarapu and Chien-Hong Cheng
Department of Chemistry, Tsing Hua University, Hsinchu
300, Taiwan
Abstract: In this article, new metal-mediated cyclization and
reductive coupling reactions of bicyclic olefins with alkynes are described.
Oxabicyclic alkenes undergo cyclization with alkyl propiolates at 80
C catalyzed by nickel complexes to give benzocoumarin derivatives in
high yields. The reaction of bicyclic alkenes (oxa- and azacyclic alkenes)
with alkyl propiolates at room temperature in the presence of the same
nickel complex gave 1,2-dihydro-napthelene derivatives in good-to-excellent
yields. This reductive coupling reaction proceeds under very mild conditions
in complete regio- and stereoselective fashion. A mechanism to account
for the coumarin formation and the reductive coupling is proposed.
*Lecture presented at the 11th IUPAC International
Symposium on Organometallic Chemistry Directed Towards Organic Synthesis
(OMCOS-11), Taipei, Taiwan, 22-26 July 2001. Other presentations are
presented in this issue, pp.1-186.
**Corresponding author.
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