Pergamon Press plc A New Convenient Method for the Synthesis of Chiral C,-Synthons

Abstract: Routes are described for the facile preparation of protected optically pure D- and Lglyceric acid (la,b; 2a,b) starting from D-mannitol, D-isoascorbic acid and L-ascorbic acid. The key step is a ruthenium catalyzed oxidative cleavage of the vicinal diols 4a.b or the a-hydroxy acids 7a,b; lOa,b. During the last decades there has been increasing interest in the synthesis of small chiral fragments which can be incorporated into optically active natural products and compounds of biological and synthetic importance’. Rxamples of such small versatile building blocks are optically pure D- and L glyceric acid derivatives, which are applied in the synthesis of chiral natural and synthetic products*. Both enantiomers can be prepared starting from D- or Lserine3 or by oxidation of the corresponding lycerol or glyceraldehyde derivatives by KMnO, 2bv4 More recently also a selective enzymatic oxidation of. protected racemic glycerol ’ and an electrochemical oxidation of D-mannitol and D-isoascorbic acid6 were reported to yield the 2,3-0-isopropylidene-D-glyceric a id (la). In this paper we report a new facile method for the synthesis of enantiomerically pure 2,3-O-isopropylidene- or 2,3-O-cyclohexylidene-D- and Lglyceric acid (la & 2a,b) by the ruthenium catalyzed oxidative cleavage of protected D_marmitol(4a,b), D-erythronic (7a,b) and Lthreonic acid (lOa,b) (Scheme I). By using this economically attractive method, both enantiomers of protected glyceric acid now become readily available starting from inexpensiv