Synthesis of seven-membered lactones via nickel- and zinc-catalyzed highly regio- and stereoselective cyclization of 2-iodobenzyl alcohols with propiolates.

Dinesh Kumar Rayabarapu, Chien-Hong Cheng

文献索引：J. Am. Chem. Soc. 124(20) , 5630-1, (2002)

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摘要

A new class of substituted seven-membered lactones 3 were conveniently synthesized via cyclization of o-iodobenzyl alcohol 1 (o-IC(6)H(4)CH(2)OH) with various propiolates 2 (RC triple bond CCOOMe) in the presence of Ni(dppe)Br(2) and Zn powder in acetonitrile at 80 degrees C. The catalytic reaction is highly regio- and stereoselective affording seven-membered lactones in moderate to good yields. This methodology can be successfully extended to various substituted o-iodobenzyl alcohols. An intermediate 7 was obtained from the reaction of 1a with methyl 2-octynoate (2a) in the presence of Ni(dppe)Br(2) and Zn at room temperature. A mechanism involving an unusual E/Z isomerization of the carbon-carbon double bond of 7 prior to lactone formation is proposed to account for the catalytic reaction.