Base catalyzed unexpected rearrangement of isatin-derived N,N′-cyclic azomethine imines and Michael addition to hindered vinylidene bisphosphonates: Access to 3,3-disubstituted oxindole-fused pyrazolidin-3-one derivatives containing bisphosphonates

A new rearrangement of isatin-derived N,N′-cyclic azomethine imines to afford intermediate 3-hydroxy-1H-pyrazole -substituted oxindole was found, and then Michael addition of them to a vinyl bisphosphonate ester provided 3,3-disubstituted oxindole-fused pyrazolidone derivatives containing bisphosphonates in the presence of the readily available DMAP. This transformation is particularly attractive due to features such as unexpected rearrangement, mild conditions, atom economy, the ready availability of the starting materials.