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

Reaction of β‐ionone with the dienynyl ether V under Neff conditions affords the C20 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 C20 carbinol with dilute acids. The dienynyl ether is synthesized from the acetal CH3COCH2CH(OCH3)2 by addition of propynyl‐lithium, subsequent reaction of the resulting C7 carbinol II with ethyl vinyl ether to yield the C7 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.