Studies on the synthesis of 3-substituted benzo[b]furanes by intramolecular S<inf>N</inf>Ar on 2-(2′-fluoroaryl)-2-(1-azolylmethyl)oxiranes

The synthesis of substituted benzo[b]furan derivatives by an approach involving opening of 2-(2′-halogenoaryl)oxiranes with base and subsequent cyclization of the alkoxide intermediate by an intramolecular SNAr reaction has been studied. Our results show that an azole moiety (imidazole, triazole) is required for the formation of benzo[b]furans. The negative charge in the intermediate carbanion is delocalized through the conjugated azole moiety (dipole stabilized side chain N-Cα carbanions). Electron-withdrawing groups in the aromatic ring favour the intramolecular cyclization. This is the case when using 2′-fluoroaryl rather than 2′-chloroaryl groups, in accordance with the leaving-group ability of fluoro and chloro groups in the SNAr reaction. This methodology involves the formation of O(1)-C(7a) bond of benzo[b]furan in the cyclization step. ©ARKAT USA, Inc.