This paper describes a study of the Ru3(CO)12-catalyzed carbonylation at an olefinic C-H bond. The reaction of pyridylolefins with CO and ethylene in the presence of a catalytic amount of Ru3-(CO)12 in toluene results in propionylation at an olefinic C-H bond in pyridylolefins. The carbonylation occurs regioselectively at a position γ to the pyridine nitrogen. Transition-metal complexes other than Ru3(CO)12, that have thus far been examined exhibit no catalytic activity, and ethylene serves as the only olefin. A similar tendency has been noted in the previously reported carbonylation at a C-H bond in the benzene ring of pyridylbenzenes. This reaction can be also applied to N-(2-pyridyl)enamines, in which an olefin unit is separated from the pyridine ring by an sp3-nitrogen atom. The reaction of N-(2-pyridyl)enamines with CO and ethylene gives the corresponding ethyl ketones as the coupling products. Interestingly, Rh4(CO)12 also shows high catalytic activity in the case of N-(2-pyridyl)enamines. In addition, olefins such as propene, 1-hexene, 3,3-dimethyl-1-butene, styrene, cyclopentene, acryl acid methyl ester, ethyl vinyl ether, and trimethylvinylsilane can also be used. This is in sharp contrast to the case of the carbonylation at a C-H bond in pyridylbenzenes reported previously and to the results of pyridylolefins as mentioned above, where Ru3(CO)12 is the only active catalyst and hexene cannot substitute for ethylene.
ASJC Scopus subject areas
- Organic Chemistry