Thermal decomposition of the 3-phenyl-substituted 2H-azaphosphirene co
mplex 1 in the presence of dimethyl cyanamide and dimethyl acetylenedi
carboxylate (DMAD) yielded dimethylamino-substituted products, the 2H-
1,2-azaphosphole complex 4b and the diastereoisomeric Delta(3)-1,3,2-o
xazaphospholene complexes 5a,b; this represents the first example of 1
,3-dipolar cycloaddition reactions of a nitrilium phosphane ylide comp
lex that is generated in situ by transylidation.