5(4H)-oxazolones. Part XI. Cycloaddition reaction of oxazolones and munchnones to triphenylvinylphosphonium salts as synthetic equivalents of alkynes

Article abstract of DOI:10.1016/S0040-4020(98)00264-6

5(4H)-Oxazolones 1 and milnchnones 3 are reacted with triphenylvinylphosphonium bromide 2a to give, through a cycloaddition reaction, pyrrole derivatives 4a-d and 7a-c unsubstituted at C-3 and C-4. The use of substituted vinylphosphonium salts 2b,c and dipoles 1 and 3 allows the isolation of 3-methylpyrroles 4e, f and 7d,e and 3-pyrrolecarboxylic acids 9a-c, respectively. The cycloaddition reactions proceed with high regionelectivity because of the positive interaction of phosphonium group of 2 and carbonyl group of dipoles 1 and 3.