Unlocking the synthetic potential of aziridine and cyclopropane-fused quinolin-2-ones by regioselective fragmentation of its three-membered rings

Abstract

The cyclization of cis-2-(2-azidophenyl)-1-benzyl-3-ethoxycarbonylaziridines and trans-2-(2-azidophenyl)-3-nitrocyclopropane-1,1-dicarboxylates yielded the respective aziridino[2,3-c]quinolin-2-ones and cyclopropa[c]quinolin-2-ones. Ring-opening of the aziridine-fused species under silica gel catalysis provided 3-aminoquinolin-2-ones whereas the ring-expansion of the cyclopropane-fused derivatives by the action of sodium hydride gave 1-benzazepin-2-ones, in both cases in a regioselective manner. A computational study using DFT methods revealed that the mechanism for the transformation of cyclopropa[c]quinolin-2-ones into 1-benzazepin-2-ones involves the initial deprotonation step of its amide function followed by two pericyclic events: a 6π-electrocyclic ring opening and a subsequent [1,5]-H shift. Keywords: Aziridino[2,3-c]quinolin-2-ones, Cyclopropa[c]quinolin-2-ones, 3-aminoquinolin-2-ones, Benzazepin-2-ones, 6π-electrocyclic ring opening, [1,5]-H shift