Esters, 4-hydroxy homoaldol reaction

Addition of a homoenolate to a carbonyl compound, which may be called a homoaldol reaction , provides a straightforward route to 4-hydroxy esters and y-lactones. Only two classes of well-characterized homoenolates that undergo nucleophilic addition to carbonyl compounds are known, namely titanium and zinc homoenolates of esters. 

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