Reaction of an oxaruthenacycle with DMAD. Stoichiometric transformations of 2,6-xylenol to allylic phenols and benzopyrans via sp(3) C-H bond cleavage reaction

摘要

Insertion of a dimethyl acetylenedicarboxylate (DMAD) into the Ru-C bond in a cycloruthenated complex Ru[OC6H3(2-CH2)(6-Me)-kappa O-2,C](PMe3)(4) (2) has been achieved to give a seven-membered oxaruthenacycle Ru[OC6H3{2-CH2C(CO2Me)=C(CO2Me)}(6-kappa O-2,C)(PMe3)(3) (3) in 47% yield. The molecular structure of 3 by X-ray analysis shows an agostic interaction between the ruthenium and one of the benzylic methylene protons. Complex 3 shows fluxional behaviour in solution and the variable temperature NMR studies suggest this fluxionality to be responsible for the turnstile rotation of three PMe3 ligands and the rotation of the a-methoxycarbonyl group. Heating of a toluene solution of 3 at 100 degrees C for 2 h results in the 1,3-H shift reaction in 3 to give a kappa O-1,eta(3)-C,C',C '' allylic complex Ru[OC6H3{2-CHC(CO2Me)CH(CO2Me)}(6-Me)-kappa O-1,eta C-3,C',C ''](PMe3)(3) (6) (80-90%), whose molecular structure is revealed by X-ray analysis. Acidolyses of 3 and 6 give 2-[(Z)-2',3'-bis(methoxycarbonyl)allyl]-6-methylphenol (7) (88%) and 2-[(Z)-2',3'-bis(methoxycarbonyl)propenyl]-6methylphenol (8) (47%), respectively, and iodolyses of 3 and 6 produce 2,3-bis(methoxycarbonyl)-8methyl-4H-benzopyran (9) (24%) and 2,3-bis(methoxycarbonyl)-8-methyl-2H-benzopyran (10) (48%), respectively.