Chemistry of acetylenic ethers 79: A new synthesis of Vitamin A aldehyde

Abstract

Abstract Reaction of β‐ionone with the dienynyl ether V under Neff conditions affords the C 20 carbinol VI, from which vitamin A aldehyde VIII can be prepared by reduction with lithium aluminium hydride and subsequent hydrolysis of the complex of the reduced C 20 carbinol with dilute acids. The dienynyl ether is synthesized from the acetal CH 3 COCH 2 CH(OCH 3 ) 2 by addition of propynyl‐lithium, subsequent reaction of the resulting C 7 carbinol II with ethyl vinyl ether to yield the C 7 diacetal III and treatment of the latter with alkali amide in liquid ammonia. The overall yield of the dienynyl ether V is about 75%, while vitamin A aldehyde is obtained in yields of 55‐60%, calculated on β‐ionone.