3-Buten-1-al derivs of formula (I): (where one of R1 and R2 is H and the other is CH3, and R3 is 1-3C alkyl, phenyl or phenyl substd. by 1-3C alkyl or alkoxy), e.g. 2-methyl-4-methoxy-3-buten-1-al, are new cpds. which are prepd. by reacting butadienes of formula (II): (where n is 0 or 1) with an alkali alcoholate or alkali hydroxide at -20 to +10 degrees C (pref. -10 to 0 degree C) in a strongly polar water-miscible solvent (pref. a saturated aliphatic alcohol or dimethylformamide). (I) are useful as intermediates for carotenoids. Thus, 3-methyl-4-methoxy-3-buten-1-al can be reacted with Cl2 in methanol/pyridine at ca - 50 degrees C, treated with sodium methoxide, reacted with beta-ionylideneethyl-triphenylphosphonium chloride or retinyltriphenylphosphonium chloride, and hydrolysed to give retinal or beta-apo-C25 carotenal in ca 80% yield. Retinal is of economic, biological and pharmacological importance, since it has vitamin A activity and is also an intermediate for beta-carotene.
展开▼
