Reaction of trimethylsilyl sulphide with phenyl isocyanate gives a 1 : 1 insertion product, but subsequent insertion of phenyl isocyanate takes place readily in the case of trialkylstannyl sulphide, to produce triphenyl isocyanurate. When chloral is used as a reactant for trialkyltin sulphides, substitution of all three chlorine atoms occurs, to afford trialkyltin chloride and (RS)3C·CHO, although a simple insertion product was obtained in the case of trialkylsilyl sulphide. Alkyl–oxygen bond cleavage of β-propiolactone has been carried out selectively for the reaction with Si–S compounds.