We
found that 1-phosphanyl-1,2,3,4-tetrahydroquinazolines undergo
ring enlargement. Their treatment with trifluoroacetic or hydrochloric
acid afforded diazaphosphepinium salts. Deprotonation of these salts
gave the corresponding neutral diazaphosphepines. The reaction of
1-phosphanyl-1,2,3,4-tetrahydroquinazolines with diazomethane or phenylazide
afforded triazaphosphocine derivatives via insertion of P–N
moiety. At the same time, an analogous hexahydropyrimidine derivative
reacted with phenylazide in a normal manner at the phosphorus atom
to afford the P(V) derivative.