Oxidative rearrangement of 2-alkoxy-3,4-dihydro-2H-pyrans: stereocontrolled synthesis of 4,5-cis-disubstituted tetrahydrofuranones

Oxidation of 2-alkoxy-3,4-dihydro-2H-pyrans with dimethyldioxirane followed by Jones oxidation leads to rearrangement and stereocontrolled formation of 4,5-cis-disubstituted tetrahydrofuranones; the method is applied to the synthesis of the whisky lactone 13 and cognac lactone 14.