Addition and cycloaddition reactions of β-chloroazo-olefins

Abstract

2-Chloro-1-(2,4-dinitrophenylazo)ethene (1a) has been isolated, and the corresponding alkoxy-carbonylazo compounds (1b) and (1c) have been generated in solution, as the first examples of azo-olefins bearing single β-halogeno substituents. The compounds (1a) and (1b) undergo [4 + 2] cycloaddition to indene and to ethyl vinyl ether with high endo stereoselectivity. Furan and cyclopentadiene give the cycloadducts (6) and (7), respectively, with (1a). Nucleophilic addition–elimination reactions are observed with piperidine, indole, thiophenol, and carbanions. In most of these reactions the primary products are subject to further nucleophilic attack: thus, the hydrazones (11) formed by addition of carbanions are converted into aminopyrroles (12) by further reaction with the carbanions and dehydration.