The synthesis of C‐2 isotopically labeled optically pure warfarin and phenprocoumon

Optically pure isotopically labeled phenprocoumon was prepared from resolved phenprocoumon via ring opening and decarboxylation followed by recarboxylation with suitably labeled ( 13 C, 14 C) diethyl carbonate and ring closure. A similar procedure was followed for the preparation of optically pure isotopically labeled warfarin after protection of the side chain carbonyl group by formation of an ethylene dithioketal derivative. The protecting group was quantitatively removed after incorporation of label by treatment with mercuric acetate.