Ru3(CO)12-Catalyzed Reaction of 1,6-Diynes, Carbon Monoxide, and Water via the Reductive Coupling of Carbon Monoxide.

We report the ruthenium-catalyzed cyclization of 1,6-diynes with two molecules of carbon monoxide and water to give a variety of catechols. This reaction likely proceeds through the intermediacy of the water-gas shift reaction to generate an yne-diol-type intermediate followed by a [4 + 2] cycloaddition with 1,6-diynes. The reaction requires no external reductants or hydride sources and provides a novel and valuable method for the synthesis of a variety of catechols.

A New Class of Redox Isomerization of N-Alkylpropargylamines into N-Alkylideneallylamines Catalyzed by a ReBr(CO)5/Amine N-oxide System.

Redox isomerization reaction wherein N-alkylpropargylamines are converted into N-alkylideneallylamines in the presence of rhenium(I) complexes as catalysts is described. Among the additives tested, certain pyridine N-oxides and tertiary amine N-oxides were effective for the reaction to proceed, and in particular, the use of 2,6-lutidine N-oxides gave the best results. The choice of a diphenylmethyl group as a substituent on the nitrogen atom was key to the success of the reaction, allowing it to reach completion.

Ir4(CO)12-Catalyzed Benzylic C(sp3)-H Silylation of 2-Alkylpyridines with Hydrosilanes Leading to 2-(1-Silylalkyl)pyridines.

The iridium-catalyzed C(sp3)-H silylation of 2-alkylpyridines with hydrosilanes at the benzylic position to afford 2-(1-silylalkyl)pyridines is described. The low product yield was markedly improved by adding 3,5-dimethylpyridine. Norbornene is also an essential additive for the reaction to proceed as a hydrogen scavenger. Carbon monoxide plays an important role in the catalytic cycle as a ligand. Other transition-metal carbonyls such as Rh4(CO)12 and Ru3(CO)12 can also be used as catalysts for this C-H silylation.

An unusual endo-selective C-H hydroarylationof norbornene by the Rh(I)-catalyzed reactionof benzamides.

Hydroarylation is an environmentally attractive strategy which incorporates all of the atoms contained in the substrates into the desired products. Almost all the hydroarylations of norbornene reported to date involve an exo-selective reaction. Here we show the endo-selective hydroarylation of norbornene in the Rh(I)-catalyzed reaction of aromatic amides. The addition of sterically bulky carboxylic acids enhances the endo-selectivity of the reaction. The results of deuterium-labeling experiments show that both the ortho-carbon and the ortho-hydrogen atoms of aromatic amides were attached to the same carbon atom of the norbornane skeleton in the hydroarylation product. These results clearly suggest that hydrometalation or carbometalation, which are commonly accepted mechanisms for the catalytic hydroarylation of C-H bonds, are not involved as the key step in the present reaction, and suggest that the reaction involves a rhodium carbene complex generated from norbornene as the key intermediate.

Conversion of 3,3,3-Trisubstituted Prop-1-ynes with tert-Butylhydrazine into 3,3,3-Trisubstituted Propionitriles Catalyzed by TpRh(C2H4)2/P(2-furyl)3.

The combination of TpRh(C2H4)2 (Tp = tris(pyrazol-1-yl)borate) and P(2-furyl)3 catalyzes the reaction of tertiary alkyl-substituted alkynes with tert-butylhydrazine, leading to the formation of 3,3,3-trisubstituted propionitrile derivatives. This reaction system is applicable to 1,1-disubstituted propargyl alcohols and amines to afford the corresponding ß-cyanohydrins and ß-amino nitriles, respectively. The catalytic cycle involves the formation of a vinylidenerhodium complex as a key intermediate.

Ni(II)-catalyzed oxidative coupling between C(sp(2))-H in benzamides and C(sp(3))-H in toluene derivatives.

Oxidative coupling between C(sp(2))-H bonds and C(sp(3))-H bonds is achieved by the Ni(II)-catalyzed reaction of benzamides containing an 8-aminoquinoline moiety as the directing group with toluene derivatives in the presence of heptafluoroisopropyl iodide as the oxidant. The method has a broad scope and shows high functional group compatibility. Toluene derivatives can be used as the coupling partner in an unreactive solvent.

Synthesis of α-silylmethyl-α,ß-unsaturated imines by the rhodium-catalyzed silylimination of primary-alkyl-substituted terminal alkynes.

In contrast to our previous report on the rhodium-catalyzed reaction of terminal alkynes with equimolar amounts of hydrosilanes and isocyanides leading to (E)- or (Z)-ß-silyl-α,ß-unsaturated imines A, the addition of an excess molar amount of hydrosilanes relative to isocyanides in the reaction of primary-alkyl-substituted terminal alkynes results in the production of α-silylmethyl-α,ß-unsaturated imines B. Various isocyanides bearing tert-butyl and 1-adamantyl groups gave B with good product selectivity. Z isomers were formed stereoselectively in many cases. Regarding the mechanism for this reaction, when the hydrosilane was added to the reaction mixture in two portions, unsaturated imines A were initially formed, which then underwent double-bond isomerization, probably catalyzed by a Rh-H species, to give B.

Rhenium-catalyzed regio- and stereoselective addition of imines to terminal alkynes leading to N-alkylideneallylamines.

The reaction of terminal alkynes with imines using ReBr(CO)(5) as a catalyst results in the production of N-alkylideneallylamines and not the conventional propargylamines. The substituent on the imine nitrogen is important, and a diphenylmethyl group gave the best result. The catalytic cycle of this regioselective C-C bond forming reaction appears to involve the formation of an alkynyl rhenium species and subsequent nucleophilic attack of the alkynyl ß-carbon atom on the imine carbon to give a vinylidene rhenium species.

Nickel-catalyzed chelation-assisted transformations involving ortho C-H bond activation: regioselective oxidative cycloaddition of aromatic amides to alkynes.

Although the pioneering example of ortho metalation involving cleavage of C-H bonds was achieved using a nickel complex (Kleiman, J. P.; Dubeck, M. J. Am. Chem. Soc. 1963, 85, 1544), no examples of catalysis using nickel complexes have been reported. In this work, the Ni-catalyzed transformation of ortho C-H bonds utilizing chelation assistance, such as oxidative cycloaddition of aromatic amides with alkynes, has been achieved.

Switch in stereoselectivity caused by the isocyanide structure in the rhodium-catalyzed silylimination of alkynes.

The reaction of terminal alkynes with hydrosilanes and tert-alkyl isocyanides in the presence of Rh(4)(CO)(12) gives (Z)-ß-silyl-α,ß-unsaturated imines in good yields. On the other hand, the use of aryl isocyanides in place of tert-alkyl isocyanides leads to the formation of E isomers.

Highly regioselective carbonylation of unactivated C(sp3)-H bonds by ruthenium carbonyl.

The regioselective carbonylation of unactivated C(sp(3))-H bonds of aliphatic amides was achieved using Ru(3)(CO)(12) as a catalyst. The presence of a 2-pyridinylmethylamine moiety in the amide is crucial for a successful reaction. The reaction shows a preference for C-H bonds of methyl groups as opposed to methylene C-H bonds and tolerates a variety of functional groups. The stoichiometric reaction of an amide with Ru(3)(CO)(12) gave a dinuclear ruthenium complex in which the 2-pyridinylmethylamino moiety was coordinated to the ruthenium center in an N,N manner.

Synthesis of [RhCl(CO)(cyclopentadienone)]2 from [RhCl(cod)]2 and a 1,6-diyne under CO: application to Rh(I)-catalyzed tandem [2+2+1] carbonylative cycloaddition of diynes and Claisen rearrangement.

Although Rh(I)Cl(CO)(cpd) (cpd = cyclopentadienone) complexes were identified more than 40 years ago, their exact structures have not been determined because of the polymeric nature of these complexes. We determined the structure of [Rh(I)Cl(CO)(cpd)](2), which was formed by the reaction of [Rh(cod)Cl](2) with a 1,6-diyne under CO. In addition, based on determination of the structure of the [Rh(I)Cl(CO)(cpd)](2) complex, we identified a new catalytic tandem reaction--the Rh-catalyzed [2+2+1] carbonylative cycloaddition of phenoxide-substituted diynes and Claisen rearrangement.

Ruthenium-catalyzed carbonylation at ortho C-H bonds in aromatic amides leading to phthalimides: C-H bond activation utilizing a bidentate system.

A new type of carbonylation of the ortho C-H bonds in aromatic amides 1, in which the pyridin-2-ylmethylamino moiety functions as a bidentate directing group, can be achieved. The presence of ethylene as a hydrogen acceptor and also of H(2)O, probably for the generation of an active catalytic species, is required. A wide variety of functional groups, including methoxy, amino, ester, ketone, cyano, chloro, and even bromo substituents, can be substituted for aromatic amides. The complex 9 was isolated by the stoichiometric reaction of 1b and Ru(3)(CO)(12), in which 1b binds to one Ru atom in the expected N,N fashion and the carbonyl oxygen binds to the other Ru atom as an O donor.

Rh(I)-catalyzed CO gas-free carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids using formaldehyde.

The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.

A chelation-assisted transformation: synthesis of maleimides by the Rh-catalyzed carbonylation of alkynes with pyridin-2-ylmethylamine.

The reaction of alkynes 1 with CO and pyridin-2-ylmethylamine (2) in the presence of Rh4(CO)12/P(OEt)3 results in the incorporation of two molecules of CO leading to maleimide derivatives 3. The coordination of the pyridine nitrogen in 2 to a rhodium center is essential for the reaction to proceed.

Rh(I)-catalyzed carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids leading to indenones.

The Rh-catalyzed reaction of alkynes with 2-bromophenylboronic acids involves carbonylative cyclization to give indenones. The key steps in the reaction involve the addition of an arylrhodium(I) species to an alkyne and the oxidative addition of C-Br bonds on the adjacent phenyl ring to give vinylrhodium(I) species II. The regioselectivity depends on both the electronic and the steric nature of the substituents on the alkynes. A bulky group and an electron-withdrawing group favor the -position of indenones. In the case of silyl- or ester-substituted alkynes, the regioselectivity is extremely high. The selectivity increases in the order SiMe3 > COOR >> aryl >> alkyl. The reaction of norbornene with 2-bromophenylboronic acids under 1 atm of CO gives the corresponding indanone derivative. The reaction of alkynes with 2-bromophenylboronic acids under nitrogen gives naphthalene derivatives, in which two molecules of alkynes are incorporated. A vinylrhodium complex similar to II can also be generated by a different route by employing 2-bromophenyl(trimethylsilyl)acetylene and arylboronic acids in the presence of Rh(I) complex as the catalyst, resulting in the formation of indenones. The reaction of 1-(2-bromophenyl)-hept-2-yn-1-one with PhB(OH)2 in the presence of Rh(I) complex also resulted in carbonylative cyclization to give an indan-1,3-dione derivative.

Rhodium-catalyzed reaction of terminal alkynes with allylamine leading to (E)-3-alkylidene N-heterocycles.

Terminal alkynes react with allylamine in the presence of a RhCl(PPh3)3 catalyst to give (E)-3-alkylidene-3,4-dihydro-2H-pyrroles. The products consist of two molecules of alkyne and one molecule of allylamine. Although dimers, trimers, and oligomers of alkynes are also obtained as byproducts, the addition of various ammonium salts to the reaction suppresses such oligomerization, resulting in an increase in product.

Chelation-assisted transformation: synthesis of 1,4-dicarboxylate esters by the Rh-catalyzed carbonylation of internal alkynes with pyridin-2-ylmethanol.

The reaction of internal alkynes 1 with CO and pyridin-2-ylmethanol (2) in the presence of Rh(4)(CO)(12) results in a double-hydroesterification leading to 1,4-dicarboxylate esters 3. The reaction does not proceed via two consecutive hydroesterifications of alkynes, but the intermediacy of ketene intermediates is proposed. The coordination of the pyridine nitrogen in 2 to rhodium is essential for the reaction to proceed. [reaction: see text]