Preparation of high specific activity all trans ‐α‐retinyl‐11‐ 3 H acetate

Lithium borotritide reduction of α‐ionylidene‐acetaldehyde (5) followed by manganese dioxide oxidation provided the tritiated aldehyde (9) which retainad over 95% of the label. On treatment with the ylide derived from ethyl 4‐chloro‐3‐methylcrotonate, ethyl α‐retinoate‐11‐ 3 H (14) was obtained which, after purification, was hydrolyzed to α‐retinoic‐11‐ 3 H acid (15). Conversion to the methyl ester (16) followed by lithium aluminum hydride reduction yielded all trans ‐ α‐retinol (17) which was isolated as the acetate derivative (18).