Stereochemical course of the photochemical transformation of 3-methyl-car-4-en-2-one into derivatives of 3,3,7-trimethylocta-4,6-dienoic acid

Abstract

Differentiation between the two vinylic methyl groups of methyl trans-3,3,7-trimethylocta-4,6-dienoate (IIa) by their nuclear Overhauser effect upon 6-H completes an elucidation of the stereochemical course of the photochemical transformation of 3-methylcar-4-en-2-one (Ia) into (IIa). The observed stereochemical course is rationalised by a non-concerted rearrangement of the diradical formed from (Ia) by α-cleavage, in which minimisation of non-bonded interactions is a controlling factor.