Synthesis and cycloaddition reactions of acetylenic iminium

0 Copyright 1976 by the American Chemical Society

VOLUME 41, NUMBER2

JANUARY 23,1976

Synthesis and Cycloaddition Reactions of Acetylenic Iminium Compounds Jonathan S. Baum** and Heinz G. Viehe Laboratoire de Chirnie Organique, Uniuersitt! de Louuain, B-1348 Louuain-la-Neuue, Belgium Received July 22,1975 Phenyl, t e r t - butyl, and unsubstituted propiolamidium tetrafluoroborate salts, prepared from ready alkylation of acetylenic amides with triethyloxonium fluoroborate, undergo facile Diels-Alder cycloaddition with cyclopentadiene. Propiolamidium salts also react easily with tetraphenylcyclopentdienone, ethyl diazoacetate, and a mesoionic oxazolium compound. A qualitative comparison of the activation of multiple bonds toward cycloaddition by the amidium group with other known substituents is discussed.

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Since electron-withdrawing substituents on acetylenes and olefins increase the rate of reaction with respect to the usual Diels-Alder addition,2 it may be anticipated that in relation to carbonyl3 and, in particular, nitro4 groups, the iminium function, >C=N