Intramolecular 1,3-dipolar cycloaddition of alkyl azidoalkylidenemalonate and 1,3-dipolar cycloreversion of the triazoline intermediate: synthesis and reactions of an N-sulphonyl-2,4-dihydropyrrolo[3,4-b]indole

Abstract

The 2,4-dihydropyrrolo[3,4-b]indole (5) was prepared by the intramolecular 1,3-dipolar cycloaddition of the azidoalkylidenemalonate (11), followed by 1,3-dipolar cycloreversion of the triazoline intermediates (12). Diels–Alder reaction of 2,4-dihydropyrrolo[3,4-b] indole derivative (6) with reactive dienophiles, such as N-phenylmaleimide, benzyne, and dimethyl acetylenedicarboxylate, gave the corresponding cycloadducts (15) and (16), (17), and (20) respectively. Arenimine (17) could be treated with lithium–ammonia to afford the dihydrobenzocarbazole (18), which was dehydrogenated by DDQ to give the benzocarbazole (19).