Chiral Phosphine-Phosphite Ligands in Asymmetric Gold Catalysis: Highly Enantioselective Synthesis of Furo[3,4-d]-Tetrahydropyridazine Derivatives through [3+3]-Cycloaddition

The Au-I-catalyzed reaction of 2-(1-alkynyl)-2-alken-1-ones with azomethine imines regio- and diastereoselectively affords furo[3,4-d]tetrahydropyridazines in a tandem cyclization/intermolecular [3+3]-cycloaddition process under mild conditions. By employing a chiral gold catalyst (prepared in situ from a Taddol-derived phosphine-phosphite ligand, Me2SAuCl, and AgOTf) high yields and enantioselectivities (up to 94% yield, up to 96%ee) are obtained. The method provides an efficient modular route to substituted heterotricyclic furan derivatives and can be easily scaled up (using catalyst loads of only 0.15 mol%).