In prwious connnunications, one of us reported that Grignard and lithium reagents attack the oxygen atoms of csrbonyl groups in c-quinol acetates (6-acetoxycyclohexa-2,k-dien-l-ones) to give slkly aryl ethers, as well as the expected products of reduction of the quinol acetates to phenols and of normal and conjugate addition to the carbonyl groups.
2 While ether formation largely superseded conjugate addition in reactions with tertiary end bensylic Grlgnard and lithium reagents, primary Grignard reagents gave only traces of products resulting from attack at carbonyl orygensa result which accounts for the fact that attack at oxygen was previously considered to occur only in a single exceptional reaction of an g-quinol diacetate.3
We have now found that dialkylmagnesiums react with o-quinol acetates to give exceptionally high ratios of yields of ethers to yields of products of conjugate addition, even when primary dialkylmagnesiums are employed. Furthermore, in reactions employing Grignard reagents, the ratio of attack at carbonyl oxygens to conjugate addition is markedly increased by a decrease in the concentration of the Grignard reagent -an effect which seems best explained by the assumption that formation of ethers by Grignard reagents (as well as reduction by'those reagents) occurs in large part through the reactions of dialkylmagnesiums, rather than of the Grlgnard reagents themselves.
The reaction of diisopropylmegnesium with 6-acetoxy-2,4,6-trimethylcyclohexa-2,k-dien-l-one (&) yields isopropyl mesityl ether ($), the conjugate addition product m&-isopropylmesitol (3). and the reduction product mesitol ($,).
The ratio of the yield of products frcm attack by the Grignard reagent at the carbonyl oxygen to the yield of products from conjugate addition is markedly affected.by the concentration of the Grignard reagent (although not by the relative concentrations of the Grignard reagent and of the quinol acetate). At high (aO.5 M) concentrations of isopropylmagnesium bromide the ratio of 5 to 3