SYNTHESIS OF NITROGEN-CONTAINING HETEROCYCLES FROM THE AZIDO-SELENENYLATION PRODUCTS OF UNSATURATED CARBONYL-COMPOUNDS

Terminal alkenes containing a remote carbonyl group reacted with iodobenzene diacetate, diphenyl diselenide, and sodium azide to afford the products of azido-phenylselenenylation of the double bond. Owing to its radical nature, this reaction proceeded with complete anti-Markovnikov regioselectivity. Under the influence of triphenylphosphine in benzene the azido group reacted with the carbonyl function to afford the corresponding ring-closure reaction products containing a carbon nitrogen double bond. Thus, starting from beta,gamma- or gamma,delta-unsaturated esters, the corresponding cyclic imino ethers were obtained. These could not be isolated but were directly transformed into beta-(phenylseleno) gamma-lactams or gamma-(phenylseleno) delta-lactams. The phenylseleno derivatives of tetrahydropyridine were formed starting both from gamma,delta-unsaturated ketones and from alpha-allyl beta-keto esters. In the latter case, the cyclization reaction is chemoselective and involves the ketonic carbonyl. The oxidation of these compounds with hydrogen peroxide directly produced the corresponding pyridines via selenoxide elimination followed by dehydrogenation. This simple reaction sequence represents a very useful general method to build up a 2-substituted pyridine ring. Several alkyl-, aryl-, and heteroarylpyridines, bipyridines, and a terpyridine have been prepared.