Misc

Here, we report that directed secondary C(sp3)–H borylation at room temperature was achieved by using phenoxyimine iridium complexes as catalysts. This reaction enables the introduction of a boryl group at the β position of a directing group, such as a pyridyl and pyrazolyl groups. Furthermore, it was indicated that the addition of a small amount of pinacolborane is important for the efficient generation of catalytically active species.

The reaction of 4,4-dimethyl-5-phenyl-4-peneten-3-one with styrene (2) using Ru(H)2(CO)(PPh3)3 as the catalyst gave the stereochemically retained product. In the case of 2,2-dimethyl-4-hexen-3-one, the stereochemically inverted branched product was obtained. These results are consistent with two different reaction pathways operating, i.e. one involving a direct C-H bond cleavage and the other, a pathway involving hydrometallation.

This paper describes a study of the Ru-3(CO)(12)-catalyzed carbonylation at an olefinic C-K bond. The reaction of pyridylolefins with CO and ethylene in the presence of a catalytic amount of Ru-3(CO)(12) in toluene results in propionylation at an olefinic C-H bond in pyridylolefins. The carbonylation occurs regioselectively ata position gamma 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 sp(3)-nitrogen atom. The reaction of N-(2-pyridyl)enamines with CO and ethylene gives the corresponding ethyl ketones as the coupling products. Interestingly, Rh-4(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 Ru-3(CO)(12) is the only active catalyst and hexene-cannot substitute for ethylene.

A ruthenium-catalyzed carbonylation at a C-H bond in a benzene ring is described. The reaction of pyridylbenzenes with CO (20 atm) and ethylene in toluene at 160°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, although this is necessary as a directing group to promote the reaction. Olefins such as trimethylvinylsilane and tert-butylethylene in place of ethylene can also be used in this reaction, however 1-hexene, cyclohexene, allyltrimethylsilane, styrene, methyl methacrylate, vinyl acetate, triethoxyvinylsilane, and isopropenyltrimethylsilane do not afford the coupling products. Transition metal complexes, other than ruthenium carbonyl, examined thus far, do not show catalytic activity. In the reaction of meto-substituted pyridylbenzenes, such as those having Me, OMe, CF 3 , and COOMe group at the meta position in the benzene ring, carbonylation takes place at the less hindered C-H bond exclusively, irrespective of the electronic nature of the substituents. It is apparent that steric factors are more important for the control of regioselectivity. 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 catalytic carbonylation reaction involving cleavage of the benzene C-H bond.

The direct carbonylation of C-H bonds in the benzene ring of N-phenylpyrazoles via catalysis by ruthenium or rhodium complexes is described. The reaction of N-phenylpyrazoles with carbon monoxide and ethylene in the presence of Ru3(CO)12 or Rh4(CO)12 resulted in the site-selective carbonylation of the ortho C-H bonds in the benzene ring to give the corresponding ethyl ketones. A variety of functional groups on the benzene ring can be tolerated. N-Phenylpyrazoles have higher reactivities than would be expected, based on the pKa values of the conjugate acid of pyrazole. The choice of solvent for this reaction is significant, and N, N-dimethylacetamide (DMA) gives the best result.

A ruthenium complex, Ru(H)(2)(CO)(PPh(3))(3), can catalyze the addition of aromatic and heteroaromatic esters at the ortho carbon-hydrogen bonds to olefinic double bonds. While un-substituted alkyl benzoate did not react, those substituted with CF3 or F underwent smooth catalytic addition. A heteroaromatic ester and a benzo-delta-lactone also reacted.

Additions of aromatic imines at the ortho carbon-hydrogen bonds to olefins were catalyzed by ruthenium complexes affording 1:1 addition products in good to excellent yields, In some cases, a by-product arising from dehydrogenative coupling was also obtained, Both aldimines and ketimines reacted well. Olefins such as styrene, 3,3-dimethyl-1-butene, and ethylene yielded corresponding products in good yields.

Catalytic C-H/olefin coupling can be directed by N,Oheterocyclic substituents. The Ru3(CO)12-catalyzed reaction of 4,4-dimethyl-2-(2-methylphenyl)-5,6-dihydro-4H-1,3-oxazine (1) with triethoxyvinylsilane gave a mixture of the corresponding 1:1 addition product (3a) and its olefinic analogue (3b) in good yields in ca. a 1:1 ratio. In the case of the reaction of 4,4-dimethyl-2-(2-methylphenyl)-4,5-dihydro-1,3-oxazole (7), the olefinic analogue (8b) of the coupling product (8a) was obtained as the major product. The existence of a new reaction pathway is discussed.

The reaction of aryloxazolines with trialkylhydrosilanes using Ru3(CO)12 or Ru(H)2(CO)(PPh3)3 complex as a catalyst resulted in dehydrogenative silylation to form ortho silylated aryloxazolines in good to excellent yields. This reaction can be applied to aryloxazolines having either electron-donating (NMe2, OMe, and CH3) or -withdrawing (CF3 and F) groups.

The reaction of 2-arylpyridines with ethylene and carbon monoxide in the presence of a catalytic amount of Rh4(CO)12 results in selective carbonylation at the ortho C-H bond. The reaction is heavily dependent on the solvents used, with DMA (N,N-dimethylacetamide) being the solvent of choice. Steric factors are also important determinants of the efficiency of the reaction. © 2005 NRC Canada.

The ruthenium-catalyzed carbonylation at a C-H bond in the benzene ring of a 2-phenyloxazoline is described. The reaction of 2-phenyloxazolines with CO and ethylene in toluene in the presence of a catalytic amount of Ru-3(CO)(12) resulted in propionylation at an ortho C-H bond in the benzene ring. The presence of the oxazoline ring on the benzene ring is essential for the carbonylation to proceed. Other heterocycles, such as oxazine, oxazole, and thiazoline rings, also served as acceptable directing groups as did the oxazoline ring. A wide functional group compatibility was observed. The site selectivity of the carbonylation was examined using meta-substituted phenyloxazolines. It was found that the carbonylation took place exclusively at the less-hindered C-H bond, irrespective of the nature of substituents, indicating that the site selectivity was determined by steric factors. The reaction was also applicable, not only to a benzene ring, but also to naphthyl and thiophenyl rings. Olefins such as propene and trimethylvinylsilane in place of ethylene could also be used in the carbonylation reaction, while other olefins, such as l-hexene, tert-butylethylene, vinylcyclohexane, isoprene, 1,5-hexadiene, cyclohexene, 1,5-cyclooctadiene, styrene, methyl acrylate, vinyl acetate, allyltrimethylsilane, and triethoxyvinylsilane did not afford the coupling products. An equilibrium between 2-phenyloxazolines, carbon monoxide, and olefins exists on one hand and the corresponding ketones on the other hand, and product composition is governed by the equilibrium thermodynamics of the system. The results of deuterium labeling experiments suggest that the catalysis involves a reversible C-H bond cleavage and that the rate-determining step is not the cleavage of a C-H bond. The results of kinetic study of the effects of CO pressure show that the reaction rate accelerates with decreasing CO pressure.

The palladium-catalyzed coupling reaction of 2-pyridyl esters with organoboron compounds is described. The reaction is compatible with various functional groups and proceeds under mild reaction conditions, The coordination of the nitrogen atom to Pd is a key step for efficient reaction.

The ruthenium-catalyzed reaction of aromatic ketones with arylboronic acid esters (arylboronates) gave the ortho arylation product. For this coupling reaction, a RuH2(CO)(PPh3)3 complex exhibited the highest catalytic activity among the complexes screened. Several aromatic ketones, for example, acetophenones, acetonaphthone, α-tetralone, and benzosuberone, can be used in this coupling reaction. A variety of arylboronates containing electron-donating (OMe and NMe2) and -withdrawing (F and CF3) groups were found to react with aromatic ketones to give the corresponding aylation products. The corresponding arylboronic acids could be used in this coupling reaction, but the yields were slightly lower, as compared to those of the reaction using the corresponding arylboronates. Copyright © 2003 American Chemical Society.

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.