Process for the preparation of .gamma., .delta.-unsaturated esters and acids

A process for the preparation of a compound of formula ##STR22## wherein symbols R.sup.1 to R.sup.7 are identical or different and each represents a hydrogen atom or an alkyl radical and R.sup.8 is an alkyl radical, which comprises the following subsequent steps:

• a. reacting an alkyl-vinyl ether of formula ##STR23## with a benzene-selenenyl halide, b. adding to the thus obtained reaction mixture an allylic alcohol of formula ##STR24## to give an acetal of formula ##STR25## c. oxidizing said acetal to give the compound of formula ##STR26## and, d. subjecting oxide (V) thus obtained to an intra-molecular thermal rearrangement to give the desired ester of formula (I) wherein R.sup.8 represents an alkyl radical.