Asymmetric synthesis of (R)- and (S)-4-(substituted benzyl)dihydrofuran-2(3H)-ones: an application of the ruthenium-binap complex-catalysed asymmetric hydrogenation of alkylidenesuccinic acids

A concise synthesis of (S)- or (R)-4-(substituted benzyl)dihydrofuran-2(3H)-ones (1) with high enantiomeric purity is presented. (S)- or (R)-(Substituted benzyl)succinic acids (6) 97% enantiomeric excess) were first prepared by Ru2Cl4[(R)- or (S)-binap)]2(NEt3) catalysed asymmetric hydrogenation of (substituted benzylidene)succinic acids. The diacids (6) were converted into (R)- or (S)-2-(substituted benzyl)butane-1,4-diols (9), and subsequent RuH2(PPh3)4-catalysed dehydrogenative lactonization of (9) afforded the lactones (1) with complete retention of configuration at the chiral centre.