In contrast to amino-imino-boranes R2N-B= NR, which are tacking the carbon atom in X= C= Y and R-CEN, respectively. susceptible to [2+ 21 cycloadditions, the amino (phosphany1- The driving force for the formation of the new heterocycles is imino) borane 2 [R'= P (~ BU)~] performs [3+ 21 cycloadditions obviously provided by the formation of an iminophosphorane with heteroallenes X= C= Y or nitriles to yield the novel five-structure and a three- ...