Synthesis of 2-phosphonopyrroles via a one-pot RCM/oxidation sequence.

A four-step synthesis of 2-phosphonopyrroles is presented starting from suitable aldehydes. The key step in the synthesis involves a one-pot ring-closing metathesis/oxidation sequence of a functionalized alpha-aminoalkenyl phosphonate. Notwithstanding the presence of a nucleophilic nitrogen atom and high substitution patterns in the substrate, the results of the RCM reaction are excellent using mild reaction conditions. Furthermore, a synergism is observed between the RCM catalyst and the oxidizing agent, causing higher oxidation rates and allowing reaction for substrates that normally fail to ring close under standard RCM conditions.