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 %.
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