Cu0-promoted cyclisation of unsaturated α-halogeno amides to give β- and γ-Lactams

Efficient 5-exo-trig atom-transfer radical cyclisation of 13 unsaturated α-halogeno amides mediated by Cu0 (copper wire) with tripyridylmethanimine ligand (TPMA; 1 mol-%) in a mixed solvent of EtOAc/EtOH (3:1) is reported (89–98 %), with recycling of the copper wire. A substantial improvement in conversion and selectivity was obtained when Na2CO3 (5 mol-%) was added to the reaction mixture. The Cu0 acts as a supplementary activator and reducing agent in a SARA-ATRC process. The protocol was extended to the cyclisation onto alkynes and the formation of β-lactams, although these reactions gave lower yields (35–76 %).