Synthesis of More Highly Oxidized Alkyl Citrates via Direct Regio- and Stereoselective Oxidation.

An approach to more highly oxidized alkyl citrates by direct regio- and stereoselective oxidations is reported. The total synthesis and structural assignment of alkyl citrate L-731-128 are described, and the synthesis of its C4 oxidized congener L-731,127 utilized a regio- and stereoselective enolate oxidation with oxygen gas. A highly stereoselective Rubottom oxidation of a cyclic silylketene acetal then enabled oxidation at C2 to afford the cinatrins C 1 and C 3 .