Adducts la-e of 2, 5-dihydr0-3-methyl-lH-phosphole with dichlorocarbene decompose at elevated temperatures, as indicated by their GC behavior and unsuccessful attempts at distillation. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) of la-e revealed an exothermic transformation in the range 100-140" C. The products obtained by heating la-d proved to be mixtures of the regioisomers of 1, 2-dihydrophosphorin 1- ...