Synthesis of 4‐Phosphinylpyrrolidin‐3‐ones via [3+2] Cycloaddition of Nitrones with Phosphinylallenes

A variety of 4-phosphinylpyrrolidin-3-ones was prepared via a [3+2] cycloaddition between aryl aldonitrones and phosphinylallenes. The products were isolated as unique 4,5-trans diastereomers, in yields up to 80% over 23 examples. In the case chiral racemic allenes, 2:1 4:1 moderate 2,5-diastereoselectivity observed. Under reaction conditions, cycloadducts directly undergo rearrangement afford selectively corresponding pyrrolidin-3-ones. DFT calculations provide some insights into mechanism, involving homolytic cleavage N–O bond cycloadduct.