Stereoselective cycloadditions of (1Z,4R,5R)-1-arylmethylidene-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines to maleimides

A library of 15 1,6,7,9-tetrasubstituted 6,7,9,9a-tetrahydro-5H-pyrazolo1,2-a]pyrrolo3,4-c]pyrazole-1,3,5(2H,3aH)-triones was prepared by combinatorial stereoselective cycloadditions of (1Z,4R^∗,5R^∗)-1-arylmethylidene-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines to N-substituted maleimides. Stereochemistry was controlled by the stereodirecting phenyl group at position-3 and by the ortho-substituents at the aromatic ring at position-1′ in azomethine imines. Consequently, two sets of diastereomeric cycloadducts were obtained, one set from the ortho-unsubstituted dipoles and the other set from the ortho-disubstituted dipoles.