Catalytic (5+1) Cycloaddition of Diazooxindoles with Imidazolidines to Access Novel Piperazine-Spirooxindole Frameworks

A catalytic (5+1) cycloaddition of diazooxindoles with imidazolidines is described, providing a general and efficient synthetic route to medicinally attractive piperazine-spirooxindole frameworks in moderate to excellent yields under rhodium or copper catalysis. Moreover, diverse transformations of the obtained products have been achieved to access more complex and even drug-derived spirooxindoles. Importantly, the asymmetric version has also been realized by employing the combination of Cu(OTf)2 and a newly synthesized SaBOX ligand (L5), leading to optically active products with up to 93:7 e.r.. This report shows that rhodium and copper are complementary catalysts for this reaction, and that copper is more competent than rhodium in catalytic asymmetric reactions involving diazocarbene-ylide intermediates.