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

Abstract

Reaction of p-ionone with the dienynyl ether V under Neff conditions affords the CZO 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 CZO carbinol with dilute acids.The dienynyl ether is synthesized from the acetal CH3COCHzCH(OCH& by addition of propynyl-lithium, subsequent reaction of the resulting C7 carbinol I1 with ethyl vinyl ether to yield the C7 diacetal Ill 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 8-ionone. Among the syntheses of vitamin A derivatives * hitherto known there are few only in which the skeleton of the twenty carbon atoms is built up with good yields in a one step reaction from b-ionone.Applying the syntheses of 1,3-enyne derivatives recently developed in our laboratory 1 , 2 7 3 , 4 , we have succeeded in preparing easily the dienynyl ether The first step in the preparation of the dienynyl ether V is a Neff reaction between propynyl-lithium and the commercially available ketobutyraldehyde dimethylacetal (I) (yield 90 %):For a review on syntheses of vitamin A and carotene derivatives see: 0. Isler and P. Schudel, "Advances in