Synthesis of cyclic aminomethylphosphonates and aminomethyl‐arylphosphinic acids by an efficient microwave‐mediated phospha‐mannich approach

Microwave‐assisted condensation of 1,3,‐2‐dioxaphosphinane 2‐oxide (1), paraformaldehyde and secondary amines including 5‐ and 6‐membered N‐heterocycles at 55°C gave cyclic aminomethylphosphonates (2), whereas an analogous reaction involving dibenzo[c.e][1,2]oxaphosphinane 2‐oxide (3) resulted in the corresponding aminomethyl‐2‐(2′‐hydroxybiphenyl)phosphinic acids (4) as a consequence of a hydrolytic ring opening following the condensation.