A new synthesis of 4‐OR‐3‐penten‐1‐ynes (C₅‐fragment) as a tool for the preparation of vitamin A

Abstract

Abstract. In our technical synthesis of vitamin A, the intermediate P-C,,-ketone (5) is obtained in a four-step sequence from p-ionone (1). In order to reduce the number of reaction steps, 1 is condensed with a C,-fragment, leading to a convergent synthesis of 5. The title compound (8) with R = -CH(OC,H,)-CH, (Si) is prepared by the reaction of 1,3-dichloro-2-propanol with ethyl vinyl ether, followed by dehydrohalogenation, substitution and isomerisation of the resulting mixed acetal (17i) in a simple one-pot procedure by treatment with sodium acetylide. The syntheses of several C,-synthons of type 8 with different groups R are described. The condensation product of 1 and 8i is partially hydrogenated and subsequently hydrolysed to 5 in an overall yield of 85 %.

β-Carotene autoxidation: oxygen copolymerization, non-vitamin A products, and immunological activity

“…In 4a, an NOE was observed between H1 and H3, whereas in 4b, the NOE was between H1 and H4. 4a has been reported in the literature, [11][12][13] but to the best of our knowledge, 4b has not (the 2E,4Z isomer has been reported 14 ). GC−MS of the 4a/4b mixture gave one peak that was identical to a reference sample of 4a.…”