Isomerisation of N-allyl-N-arylethanamides catalysed by ruthenium complexes

The isomerisation of N-allyl-N-arylethanamides having a general formula of AcN(Ar)allyl (Ar = Y-C6H4- where Y = H; o-, m-, P-OMe; o-, p-Br, Cl, Me, O2N; Ar = 1- and 2-naphthyl) catalysed by ruthenium complexes-mostly by [RuClH(CO)(PPh3)3] has been studied. N-Allyl-N-arylethanamides were obtained by allylation of respective N-arylethan-amides in the PTC conditions (excess of allyl chloride, 50% aq. NaOH, NBu4+HSO4-). The products of isomerisation (reaction conditions: 0.5% mol [RuClH(CO)(PPh3)(3)], 120degreesC, 2-16 h) were mostly or practically solely (E)-N-aryl-N-(1 -propenyl)-ethanamides. It is proposed that the observed selectivity of the double bond migration to (E)-enamides is a result of the interaction of the arene ring with the Ru atom in the transition states. Quantum calculations (PM5 method) done for N-allyl-N-arylethanamides and for (E)- and (Z)-N-aryl-N-(1 -propenyl)ethanamides (aryl = Y-C6H4- where Y = H; o-, m-, p-OMe; o-, p-Br, Cl, Me, O2N) as well as results of isomerisation of AcN(R)allyl (R = H or cyclohexyl) amides support this assumption. Moreover, the impact of substituents in Y-C6H4N(Ac)allyl and solvents on the rate of the double bond migration has been studied. The structure of the complexes forming in the course of the reaction and the reaction mechanism are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.