Application of pentacoordinated spirophosphorane as a new organocatalyst for the Michael addition reaction

Pentacoordinated spirophosphorane as a simple, effective and novel organocatalyst for the Michael addition reaction has been investigated. The bisaminoacyl spirophosphorane that possessed a thiourea-like moiety and an amine group was applied to the Michael addition reaction of 1, 3-dicarbonyl compound with beta-nitrostyrene, affording the desired adduct in good yield. Furthermore, the mechanism of the Michael addition reaction catalyzed by spirophosphorane was proposed with the help of the analysis of single crystal structure, NMR experiments. It was identified that 1, 3-dicarbonyl compound and beta-nitrostyrene formed hydrogen bonds with amine group and N-H groups of spirophosphorane catalyst, respectively. Then the two reactants approached each other, and the methylene of 1, 3-dicarbonyl compound attacked the olefin carbon of beta-nitrostyrene to form nucleophilic addition product. This report is the first example of spirophosphorane as a novel organocatalyst to successfully catalyze the Michael addition reaction.