Electro-organic reactions. Part 42. The diastereoselective cathodic hydrodimerisation of cinnamate esters; preparative aspects

Abstract

The cathodic reduction of cinnamate esters formed with chiral alcohols proceeds smoothly via coupling and intramolecular condensation, with high stereoselectivity, to give good yields of diastereoisomeric mixtures of the esters of the all-trans(±)-2-carboxy-3,4-diphenylcyclopentanone. Eight examples have been studied in detail and a diastereoisomeric excess of >95% is achieved using the bornyl ester. Choice of electrolyte cation (Li⁺ or Et₄N⁺) does not influence yield or stereoselectivity. In some other cases cleavage with loss of cinnamic acid is the preferred reaction. meso Isomers are not formed in the cyclic hydrodimerisation reaction. Pure diastereoisomers are easily isolated by fractional crystallisation and may be converted into (±)-3,4-diphenylcyclopentanone.