Grignard reagents ester reactions with

When the carbonyl carbon is substituted with a potential leaving group, the tetrahedral adduct can break down to regenerate a C=0 bond and a second addition step can occur. Esters, for example are usually converted to tertiary alcohols, rather than ketones, in reactions with Grignard reagents. 

In the initial discovery of the asymmetric synthesis of a-chloro boronic esters 3, the diastereomeric ratios of 3 were estimated by reaction with Grignard reagents to form secondary alkyl boronic esters 5 and deboronation with hydrogen peroxide to secondary alcohols of known absolute configuration and rotation40. 

The ester moiety of methyl 2-methoxy-4-furoates underwent the usual addition reaction with Grignard reagents to provide tertiary alcohols, as exemplified in Equation (172). However, displacement of the 2-methoxy group of the corresponding 3-furoate isomers occurred under the same reaction conditions, presumably via a six-membered organomagnesium chelate, to give 2-substituted-3-furoates as the major products (Equation 173) <2003TL5781>. 

Problem 20.21 (a) Esters of which acid would yield secondary alcohols on reaction with Grignard reagents (b) Starting from alcohols of four carbons or fewer, outline all steps in the synthesis of 4-heptanol. 

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