Asymmetric intramolecular C-H/olefin coupling reactions of 1-(2-pyridyl)- or 1-(1- methyl-2-imidazolyl)-1,5-dienes are catalyzed by a rhodium complex having a homochiral monodentate phosphine ligand.
Ruthenium- and rhodium-catalyzed intramolecular C–H/olefin coupling reactions of 1-(2-pyridyl)-, 1-(2-imidazolyl)-, and 1-(2-oxazolyl)-1,5-dienes proceeded in a regiospecific manner to give 5-membered ring products. Their 1,6-diene analogues are also applicable to the cyclization reaction to give the corresponding 5- and 6-membered carbocycles. For the cyclization of the pyridine derivatives, [RhCl(PPh3)3] showed the highest catalytic activity with respect to efficiency and selectivity. When the imidazole derivatives were employed to the cyclization reaction, the combination of the rhodium(I) complex and the relatively sterically bulky phosphine (e.g., PCy3 and PPFOMe) was a quite effective catalyst system. In the case of the oxazoles, the ruthenium complex, [Ru(H)2(CO)(PPh3)3], showed the highest activity among the catalysts examined. These catalytic reactions usually proceed at 120 °C. The [RhCl(PPh3)3]-catalyzed cyclization reaction of 2-[(1E)-4,4-dimethyl-1,5-hexadienyl]pyridine smoothly proceeded even at room temperature to give the corresponding cyclized product in 93% yield after 24 h. A hybrid catalyst system containing the rhodium(I) and both PPh3 and P(o-tolyl)3 had a slightly better catalytic activity compared with that of [RhCl(PPh3)3]. The intramolecular cyclization can be also applied to the C–H/CO/olefin coupling reactions. These carbonylation reactions gave the 5-membered ring ketones exclusively. The intramolecular C–H/olefin coupling reactions provide a new entry for constructing carbocyclic compounds from 1,n-dienes.
A combination of aluminum compounds and organic sulfonic acids was an efficient catalyst system for direct methyl levulinate synthesis from both microcrystalline cellulose and wood powder.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.