A coordinatively unsaturated ruthenium methoxide as a highly effective catalyst for the halogen atom-transfer radical cyclization of N-allyl dichloroacetamides and related reactions

Atom-transfer radical cyclization (ATRC) catalyzed by coordinatively unsaturated ruthenium alkoxides 4, [(eta(5)-C5Me5)-Ru(OR)](2), is investigated, and ruthenium methoxide 4a (R=Me) is found to exhibit excellent catalytic activity for the cyclization of N-allyl-alpha,alpha-dichloroacetamides at ambient temperature. Addition of some amounts of two-electron donor ligands such as pyridine and triphenylphosphine improves the catalyst efficiency to afford the corresponding gamma-lactams in high yields. The high catalytic activity of this catalyst system enables to control the diastereoselectivity of this 5-exo cyclization kinetically. The present 4a/pyridine system is also effective for the 4-exo cyclization of N-vinylacetarnides to afford the corresponding beta-lactams in quantitative yields. The 4a/pyridine system is also active towards the ATRP of methyl methacrylate (MMA) at room temperature to afford the poly(MMA) with narrow molecular weight distributions (M-w/M-n = 1.2) at the initial stage. (c) 2006 Elsevier Ltd. All rights reserved.