Indirect electroreductive cyclisation of N-allylic and N-propargylbromo amides and o-bromoacryloylanilides using nickel(II) complexes as electron-transfer catalysts

Nickel(II) complex-catalysed indirect electroreduction of N-allylic and N-propargyl-α-bromo amides and o-bromoacryloylanilides gave the corresponding 5-membered lactams. The product distribution was affected by the ability of the solvent to donate hydrogen atom. The electroreduction of N-allyl-N(bromoacetyl)toluene-p-sulfonamide 1a in DMF and acetonitrile yielded as main product the 4-methylpyrrolidinone 2a(41%) and the 4-(bromomethyl)pyrrolidinone 3a(33%), respectively. On addition of 2 mol equiv. of a hydrogen-atom donor (Ph2PH) to the reaction of bromo amide 1a in acetonitrile, compound 1a provided compound 2a(58%) as the sole cyclised product.