The conjugate addition of phenylmagnesium bromide to benzalacetoinesitylene (1) was studied. The only product resulting from 1, 4-addiaon was Kohler's ketone (4) in 84±1% yield based on (1) by isolation and analysis. The byproducts from 4 were formed mainly by oxidation of the Z enol of 4 to the α-ketohydroperoxide (6) during the hydrolysis and workup of the product followed by subsequent decomposition of 6 to diphenylethanal and a trace ...