RU-3(CO)(12)-CATALYZED REACTION OF PYRIDYLBENZENES WITH CARBON-MONOXIDE AND OLEFINS - CARBONYLATION AT A C-H BOND IN THE BENZENE-RING

A ruthenium-catalyzed carbonylation at a C-H bond in a benzene ring is described. The reaction of pyridylbenzenes with CO (20 atm) and ethyl ene in toluene at 160 degrees C in the presence of a catalytic amount of Ru-3(CO)(12) results in propionylation at an ortho C-H bond in the benzene ring, Carbonylation does not occur at the pyridine ring, altho ugh this is necessary as a directing group to promote the reaction. Ol efins such as trimethylvinylsilane and tert-butylethylene in place of ethylene can also be used in this reaction, however I-hexene, cyclohex ene, allyltrimethylsilane, styrene, methyl methacrylate, vinyl acetate , triethoxyvinylsilane, and isopropenyltrimethylsilane do not afford t he coupling products, Transition metal complexes, other than ruthenium carbonyl, examined thus far, do not show catalytic activity. In the r eaction of meta-substituted pyridylbenzenes, such as those having Me, OMe, CF3, and COOMe group at the meta position in the benzene ring, ca rbonylation takes place at the less hindered C-H bond exclusively, irr espective of the electronic nature of the substituents, It is apparent that steric factors are more important far the control of regioselect ivity. The reaction is also applicable to naphthyl and thienyl rings, Six-membered heterocycles, such as 2-pyrimidine and 4-pyrimidine, are also effective directing groups for carbonylation at a C-H bond in the benzene ring. The present reaction represents the first, effective ca talytic carbonylation reaction involving cleavage of the benzene C-H b ond.