Enantioselective copper catalysed C–H insertion reaction of 2-sulfonyl-2-diazoacetamides to form γ-lactams
The first examples of asymmetric copper-catalysed intramolecular C–H insertion reactions of 2-sulfonyl-2-diazoacetamides are described; trans γ-lactams with up to 82% ee are achieved with the CuCl2-bisoxazoline-NaBARF catalyst system. The reactions generally display high efficiency and high trans selectivity, and also a strong regiochemical preference for insertion to lead to the formation of 5-membered rings over 4-membered rings. In cases where there are competing C–H insertion pathways available, to form sulfolanes or thiopyrans, only the insertion into the amide chain to form γ-lactams is observed. With phenylsulfonyl derivatives, a minor competing C–H insertion pathway leading to β-lactams is seen; interestingly, changing the identity of the copper ligand changes the product ratio of β/γ-lactams. The copper catalysed reactions compare favorably in terms of efficiency and enantioselectivity to the corresponding reactions catalysed by commercially available chiral rhodium catalysts.