STUDIES ON THE ROLE OF THE 2-OXONIA COPE REARRANGEMENT IN PI-CYCLIZATIONS OF ALPHA-METHOXYCARBONYL OXYCARBENIUM IONS

[摘要] The 2-oxonia Cope rearrangement is shown to play an important role in Lewis acid-induced R-cyclization reactions of a variety of methyl 2-acetoxy-2-(3-alken-I-oxy)acetates to 5- and 6-membered ring ethers. The influence of this [3,3]-sigmatropic rearrangement on the regio- and stereochemical outcome of the cyclization is evaluated by studying three types of substrates, namely (1) four chain-substituted precursors, (2) three silicon-substituted precursors (allyl- and vinylsilanes) and (3) two enantiopure precursors. Controlling factors are the nature of the ri-nucleophile and the substitution pattern of the oxycarbenium ton intermediate. The absolute stereochemistry is retained in the cyclization of the enantiopure substrates.

[发布日期] 1994-06-13