Synthesis and Dimethyldioxirane Oxidation of Tetrahydrobenzofurans

Abstract

On treatment with alkaline hydrogen peroxide (Weitz−Scheffer oxidation), the N-(5,6,7,8-tetrahydro-2,5-dioxo-2H-1-benzopyran-3-yl)benzamides 1a−c afforded the N(4-oxo-4,5,6,7-tetrahydro-1-benzofuran-2-yl)benzamides 2a−c in an unprecedented transformation. These hitherto unknown tetrahydrobenzofuran derivatives have been converted into 2-hydroxy-2-(4-oxo-2-phenyl-4,5-dihydro-1,3-oxazol-5-yl)cyclohexane-1,3-diones 3a−c by dimethyldioxirane oxidation. Proposed mechanisms for the formation of the furans 2a−c and the 2-hydroxycyclohexane-1,3-diones 3a−c are offered. Structure elucidation of all new compounds has been performed by NMR spectroscopy. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)