Synthesis of compounds containing the isoprene unit. A new stereoselective synthesis of all-trans vitamin A and of methyl (2E,4E)-3,7,11-trimethyldodeca-2,4-dienoate

Methyl (2E,4E)-3,7,11-trimethyldodeca-2,4-dienoate (8b), a potent insect growth regulator, is synthesized from the dianion of 3-methylbut-3-en-1-ol (2) and tetrahydrocitral (3). Elimination of acetic acid to (8b) in (2E,4E) configuration is achieved by treatment of the intermediate acetoxy-ester (7b) with a base (NaH, KH, or ButOK) in the presence of a catalytic amount of crown ether in hexane. Following the same scheme, a new synthesis of Vitamin A via all-trans retinal is achieved.