Synthesis and stereochemistry of the epoxides of 2-arylmethylidene-1-tetralones

Abstract

Oxidation of both the E and Z isomers of the 2-arylmethylidene-l-tetralones 1 by alkaline hydrogen peroxide afforded the spiroepoxides trans-2a–g as sole products in high yields. In contrast, the dimethyldioxirane epoxidation of the E isomers la–g gave the corresponding trans spiroepoxides in good yields, while the Z isomers 1a,c,e yielded the respective cis spiroepoxides in moderate yields. Epoxidation of (Z)-1a,c,e by m-chloroperoxybenzoic acid yielded ca. 6 : 1 mixtures of cis-2a,c,e and trans-2a,c,e spiroepoxides. Separation of the isomeric epoxides was achieved by silica gel chromatography and their structures, relative configurations and stereochemistry were elucidated by NMR spectroscopy.