Unexpected chiral vicinal tetrasubstituted diamines via borylcopper-mediated homocoupling of isatin imines

Addressing the asymmetric synthesis of oxindole-based a-amino boronic acids, instead of the expected products we disclosed the efficient homocoupling of oxindole-based N- tert -butanesulfinyl imines, with the generation of chiral, quaternary 1,2-diamines in a mild and completely stereoselective way. The obtained 3,3′-bisoxindoles derivatives were fully characterised by NMR and single-crystal X-ray diffraction analysis and proved to be single diastereoisomers and atropoisomers. A plausible mechanism for the one-pot Cu(II)-catalysed Bpin-addition to the isatin-derived ketimine and subsequent homocoupling is detailed.