Available hemiacetals and hemithioacetals of alpha-halo-beta-oxoaldehydes were reacted with phosphorochloridites in the presence of organic bases to obtain previously unknown alpha-heterosubstituted phosphites. It is found that the phosphites, depending on the nature of the carbonyl fragment and the heteroatom, enter intramolccular Perkow reaction or decompose to give unsaturated thioethers and chlorophosphate.