Base-Catalyzed Intramolecular [4+2]-Cycloaddition of [3-Arylprop-2-yn-1-yl](3-phenylprop-2-en-1-yl)ammonium Bromides and Cleavage of the Cycloaddition Products in Aqueous Alkali

Abstract

Study of the intramolecular cyclization of [3-(4-bromo(or methyl)phenylprop-2-yn-1-yl](3-phenylprop-2-en-1-yl)ammonium bromides has shown that the presence of a bromine atom or methyl group in the para position of the aromatic ring inhibits the process. 6-Bromo(or methyl)-4-phenyl-2,3,3a,4-tetrahydro-1H-benzo[f]isoindol-2-ium bromides undergo cleavage in aqueous alkaline medium at both N²-C³ and C¹-N² bonds, whereas cleavage of 6-methyl-4-phenyl-1,3,3a,4-tetrahydrospiro[benzo[f]isoindole-2,4′-morpholin]-2-ium bromide follows only the latter path. An accessible method has been developed for the synthesis of 6-bromo(or methyl)-4-phenyl-2,3,3a,4-tetrahydro-1H-benzo[f]isoindol-2-ium bromides, isomeric N-[7-bromo-2(3)-methyl-1-phenylnaphthalen-3(2)-ylmethyl]piperidines and -morpholines, and their 7-methyl-substituted analogs.