Stereoselective reduction and reductive dephosphonylation of β-iminophosphonates

Proline-like 2,4-dialkyl-5-phosphonylpyrrolidines 2 were obtained stereoselectively by reduction of the corresponding β-iminophosphonates 1 with NaBH4. The detailed characterization of compounds 2 was accomplished by 1H and 13C NMR as well as by crystal structure analysis. When 1 was reduced with LiAlH4 the reaction gave dephosphonylated pyrrolidines 3. The latter method is suitable for providing substituted pyrrolidines regioselectively. A possible mechanism for the dephosphonylation is proposed.