The photochemical transformation of 3-methylcar-4-en-2-one into derivatives of 3,3,7-trimethylocta-4,6-dienoic acid. Revised stereochemical assignments

Abstract

The stereochemical assignments made by Baldwin and Krueger for the photochemical transformation of 3-methylcar-4-en-2-one into derivatives of 3,3,7-trimethylocta-4,6-dienoic acid have been reinvestigated and revised. The stereochemistry of alkylation of eucarvone to give 3-alkylcar-4-en-2-one derivatives was found to occur as expected, from the least hindered face of the intermediate anion. Differentiation between the two methyl groups of 4-methylpenta-1,3-diene by n.m.r. spectroscopy (chemical shift difference 0·02 p.p.m.) was accomplished by utilising the thermal [1,5] hydrogen migration in 5,5,5-trideuterio-4-trideuteriomethylpenta-1,3-diene.