1,3,4‐Thia(selena)azaphospholines and phospholidines

O-Phenyl chloromethyldithio- and chloromethylselenothiophosphonic acids, formed by the reaction of O-phenyl chloromethyl-(chloro)thiophosphonate with hydrogen sulfide or hydrogen selenide, respectively, in the presence of Et3N, react in situ with alkyl thiocyanates and bis(thiocyanato)methane, yielding 2-alkylithio-4,5-dihydro-4-thioxo-4-phenoxy-1,3,4-thia-(selena)azaphospholes and 2,4-dithioxo-4-phenoxy-1,3,4-thia(selena)azaphospholidines, respectively.