Synthesis of intermediates for vitamin A

#Vitamin A is a known organic substance which is essential for growth and for maintaining animal life but which cannot be synthesized by the animal nor provide energy by itself. Because of its importance, numerous attempts have been made to synthesize Vitamin A. In 1947 Hoffmann-LaRoche reported the first successful laboratory synthesis of Vitamin A, marking the culmination of what had been a formidable scientific and economic challenge to the organic chemist for several decades. Since that time a number of different syntheses of Vitamin A have been suggested but most are not considered commercially feasible.

#Vitamin A is generally considered to have this formula: ##STR1##

#It is important to distinguish between the cis and trans forms of Vitamin A. The trans form has much higher biological activity than any of the possible cis forms. Likewise, compounds of the above formula in which all double bonds are shifted one carbon atom to the left are only very slightly active.

#The following examples only illustrate the invention and are not intended to limit the claims. Temperatures are on the Centigrade scale unless otherwise indicated.

#Beta-ionone was reacted with lithium acetylide in a known manner to produce ethynyl-beta-ionol. The etherification of tertiary alcohols is known to be difficult and usually results in poor yields. When an --OH group is hindered, diminishing its tendency to form alkoxide ions, additional difficulty is encountered upon attempted etherification. Unfortunately, all of these factors prevail in ethynyl-beta-ionol.

#Ethynyl-beta-ionol has been successfully converted in the present invention to its lower alkyl ethers by use of alkyl sulfates, using an aprotic solvent such as dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF) is basic medium, using a base such as NaOH or Ba(OH).sub.2. The yields are excellent, running around 90 percent. In one example, the following components were used: