Construction of dihydro-1,4-dioxins: Synthesis of dihydro-1,4-dioxin-3-carboxanilides

A new methodology for construction of dihydro-1,4-dioxin skeleton was descr ibed. Introduction of thio group at the alpha -position of 8 followed by ch lorination gave 11, which was to prevent an enolization as well as to promo te the facile nucleophilic substitution reaction of ethylene glycol giving 16 in equilibrium with cyclic ether 19. Removal of thio group of 19 and deh ydration in the presence of an acid catalyst gave dihydro-1,4-dioxin 21. In case of electron withdrawing trifluoromethyl group is subsituted in C-2, 1 8 was converted to the corresponding dihydro-1,4-dioxin 20 by the halogenat ion of hydroxy followed by treatment of triethylamine.