Imidoyl Radicals for the Synthesis of Chromenoquinolines and Naphthyridines

Abstract

The stability of imidoyl radicals prepared from 2-(2-alkenyloxy)-phenyl selenoimidates and 2-(2-allylamino)-phenyl selenoimidates and their intramolecular free radical cyclization through the slow addition of tri-N-butyltin hydride and AIBN to obtain 4-chromanones and 4-quinolones were studied. The extension of the methodology to N-phenyl substituted imidoyl selenoates produced tandem cyclizations of the imidoyl radical with the allyl substituent, followed for a second cyclization of the intermediate radical with the aromatic substituent to produce dihydro-chromenoquinolines or tetrahy-dro-dibenzonaphtyridines. Further oxidation with DDQ produced: 6H-chromeno [4,3,b] quinoline and 7-methyl-6H-chromenoquinoline from 2-alkenylamino-phenylbenzamide and 5,6-dihydro-dibenzo [b,h][1,6] naphthyridine and 5,6-dihydro-7-methyl-dibenzo [b,h][1,6] naphthyridine from 2-2-(alkylamino)-N-phenylbenzamides. The cyclization of 2-(N,N-di-prop-2.enylamino)-N-phenylnicotinamide selenoate obtained from 2-aminonicotinic acid, produced 5,6-dihidro-benzo[b]pyrido2,3-h] [1,6] naphthyridine.