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

Abstract

Atom-transfer radical cyclization (ATRC) catalyzed by coordinatively unsaturated ruthenium alkoxides 4 , [(η 5-C 5Me 5)Ru(OR)] 2, is investigated, and ruthenium methoxide 4a (R=Me) is found to exhibit excellent catalytic activity for the cyclization of N-allyl-α,α-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 γ-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-vinylacetamides to afford the corresponding β-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.