FOERFARANDE FOER FRAMSTAELLNING AV ERYTRO-DIHYDROXIALKENSYRADERIVATER

The invention provides a novel process for the manufacture of [2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-phenylfurans of the formula IIa, useful as intermediates in the production of novel (4-phenyl-1,3-dioxan-cis-5-yl)alkenoic acids of the formula I in which Ra and Rb are independently hydrogen, alkenyl, alkyl, halogenoalkyl, pentafluorophenyl, aryl or aryl-(1-4C)alkyl; or Ra and Rb together are polymethylene; Rc is hydroxy or (1-6C)alkanesulphonamido, A is vinylene, n is 1, Y is polymethylene, and benzene ring B bears various optional substituents. The compounds of formula I are obtained by the reaction of an aldehyde of formula II with an ylid to give an erythro-diol of formula III which is then cyclised to the required dioxane derivative of formula I. The aldehydes of formula II are obtained from the corresponding lactols of formula IIa, which are themselves obtained with the correct trans-stereochemistry by the inventive process using two selective reductions of a trans-phenylparaconic acid of formula V. The compounds of formula I are useful as therapeutic agents.