Reaction of an oxaruthenacycle with DMAD. Stoichiometric transformations of 2,6-xylenol to allylic phenols and benzopyrans via sp3 C–H bond cleavage reaction

Abstract

Insertion of a dimethyl acetylenedicarboxylate (DMAD) into the Ru-C bond in a cycloruthenated complex Ru[OC(6)H(3)(2-CH(2))(6-Me)-kappa(2)O,C](PMe(3))(4) () has been achieved to give a seven-membered oxaruthenacycle Ru[OC(6)H(3){2-CH(2)C(CO(2)Me)[double bond, length as m-dash]C(CO(2)Me)}(6-Me)-kappa(2)O,C](PMe(3))(3) () in 47% yield. The molecular structure of by X-ray analysis shows an agostic interaction between the ruthenium and one of the benzylic methylene protons. Complex shows fluxional behaviour in solution and the variable temperature NMR studies suggest this fluxionality to be responsible for the turnstile rotation of three PMe(3) ligands and the rotation of the alpha-methoxycarbonyl group. Heating of a toluene solution of at 100 degrees C for 2 h results in the 1,3-H shift reaction in to give a kappa(1)O,eta(3)-C,C',C'' allylic complex Ru[OC(6)H(3){2-CHC(CO(2)Me)CH(CO(2)Me)}(6-Me)-kappa(1)O,eta(3)C,C',C''](PMe(3))(3) () (80-90%), whose molecular structure is revealed by X-ray analysis. Acidolyses of and give 2-[(Z)-2',3'-bis(methoxycarbonyl)allyl]-6-methylphenol () (88%) and 2-[(Z)-2',3'-bis(methoxycarbonyl)propenyl]-6-methylphenol () (47%), respectively, and iodolyses of and produce 2,3-bis(methoxycarbonyl)-8-methyl-4H-benzopyran () (24%) and 2,3-bis(methoxycarbonyl)-8-methyl-2H-benzopyran () (48%), respectively.