Reaction of Nitrones with Phosphinylallenes: DFT Mechanistic Investigations

The reaction between phosphinylallenes and nitrones efficiently leads to 4-phosphinylpyrrolidin-3-ones. The mechanism involved in this reaction was theoretically studied to understand the overall pathway and the stereochemical outcome of the transformation. The first step of the mechanism is a (3+2) cycloaddition between the nitrone and the allene delivering an isoxazolidine ylidene intermediate. This never isolated intermediate undergoes a spontaneous rearrangement to the final 4-phosphinylpyrrolidin-3-one through the homolytic N–O bond cleavage followed by rotation and C–N recombination of the biradical intermediate. The computational results obtained from this study are highly informative for potentially obtaining diastereoisomerically and enantiomerically pure 4-phosphinylpyrrolidin-3-ones by a judicious choice of substituents on nitrone and allene.