American Chemical Society
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Palladium-Catalyzed Synthesis of Endocyclic Allenes and Their Application in Stereoselective [2 + 2]Cycloaddition with Ketenes

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journal contribution
posted on 2009-01-01, 00:00 authored by Masamichi Ogasawara, Atsushi Okada, Kiyohiko Nakajima, Tamotsu Takahashi
Palladium-catalyzed reactions of various 2-bromo-3-exo-methylenecycloalkenes with a stabilized nucleophile were examined. When the carbocycles were nine-membered or larger, the corresponding endocyclic allenes were isolated in excellent yields. In a reaction of the eight-membered cyclic substrate, initial formation of a cycloocta-1,2-diene derivative was detected; however, it dimerized slowly. The seven-membered carbocycle was inert to the reaction. Using a chiral Pd-catalyst, an axially chiral endocyclic allene was obtained in 65% ee. The cyclic allenes were applied to [2 + 2]cycloaddition with ketenes, and the stereoselectivity was studied.