Polyene glycols and acetoxy-polyene glycols by pinacolic reduction of polyene aldehydes

摘要

The invention comprises polyene a -glycols of the formula FORM:1097497/C2/1 where the radicals R represent saturated or unsaturated, unsubstituted or acetoxy-substituted aliphatic hydrocarbon radicals and both R1's are hydrogen or methyl radicals, and the preparation thereof by contacting a polyene aldehyde of the formula FORM:1097497/C2/2 with zinc in a liquid reaction medium which is pyridine, a 4-n-C1- 3 alkyl pyridine, 3-methyl pyridine or a mixture thereof, the mole ratio of zinc to aldehyde being at least 1. Specified polyene a -glycols are retinal pinacol, 13-cisretinal pinacol, 3,4-dehydroretinal pinacol, 4-acetoxy-retinal pinacol and sorbaldehyde pinacol. The zinc may be employed as, e.g., zinc dust, zinc amalgam, zinc bismuth or zinc copper, all of which are preferably washed with a strong mineral acid and water before use. It is preferred to effect the reaction at 0-75 DEG C. in the presence of at least 2 volumes liquid reaction medium per volume of aldehyde. Retinal pinacol diacetate is prepared by reacting retinal pinacol with acetic anhydride. Retinal pinacol dimethyl ether is prepared by reacting retinal pinacol with acetone and methyl iodide in the presence of potassium hydroxide. b -Carotene is prepared by reacting retinal pinacol with carbon disulphide, pyridine and phosphorus triiodide. Dehydroretrocarotene is prepared by reacting retinal pinacol with diethyl ether and hydrochloric acid.