A new sterically highly hindered 7-membered cyclic nitroxide for the controlled living radical polymerization

The synthesis of a new sterically highly hindered 7-membered alkoxyamine, 2,2,7,7-tetraethyl-1-(1-phenylethoxy)-1,4-diazepan-5-one (4), starting from known 2,2,6,6-tetraethyl-1-(1-phenylethoxy)piperidin-4-one (3) via a Beckmann-type rearrangement is presented. It is shown that ring-enlargement by insertion of an NH moiety in going from 3 to 4 leads to a more efficient regulator for nitroxide-mediated controlled living radical styrene (=ethenylbenzene) and butyl acrylate (=butyl prop-2-enoate) polymerization. In addition to the polymerization experiments, kinetic data on the reversible C-O bond homolysis of alkoxyamines 3 and 4 are presented.