Alkylative Carboxylation of Ynamides and Allenamides with Functionalized Alkylzinc Halides and Carbon Dioxide by a Copper Catalyst.

The alkylative carboxylation of ynamides and allenamides with CO2 and alkylzinc halides catalyzed by a copper catalyst was developed. A variety of alkylzinc halides bearing functional groups were used for this transformation to afford α,ß-unsaturated carboxylic acids, which contain the α,ß-dehydroamino acid skeleton, introducing the corresponding alkyl group and CO2 across the carbon-carbon triple or double bond. This alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides or allenamides with alkylzinc halides and the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2 . This protocol would be a useful method for the synthesis of α,ß-dehydroamino acid derivatives possessing a functionalized alkyl group due to the high regio- and stereoselectivity, simple one-pot procedure as well as the use of CO2 as a starting material.

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex.

The alkylative carboxylation of allenamide catalyzed by an N-heterocyclic carbene (NHC)-copper(I) complex [(IPr)CuCl] with CO2 and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2 (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)-α,ß-dehydro-ß-amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ-carbon, and the carboxyl group introduced onto the ß-carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2 . A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing ß-hydrogen atoms, such as Et2 Zn or Bu2 Zn, also gave the corresponding alkylative carboxylation products without ß-hydride elimination. The present methodology provides an easy route to alkyl-substituted α,ß-dehydro-ß-amino acid ester derivatives under mild reaction conditions with high regio- and stereoselectivtiy.

Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide.

Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N-heterocyclic carbene (NHC)-copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,ß-unsaturated carboxylic acids, which contain the α,ß-dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2 . Dialkylzinc reagents bearing a ß-hydrogen atom such as Et2 Zn and Bu2 Zn still afford the alkylated products despite the potential for ß-hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,ß- dehydroamino acid derivatives due to its high regio- and stereoselectivity, simple one-pot procedure, and its use of CO2 as a starting material.

Efficient and chemoselective imine synthesis catalyzed by a well-defined PN3-manganese(II) pincer system.

The highly efficient reductive amination of aldehydes with ammonia (NH3) and hydrogen (H2) to form secondary imines is described, as well as the dehydrogenative homocoupling of benzyl amines. Using an air-stable, well-defined PN3-manganese(II) pincer complex as a catalyst precursor, various aldehydes are easily converted directly into secondary imines using NH3 as a nitrogen source under H2 in a one-pot reaction. Importantly, the same catalyst facilitates the dehydrogenative homocoupling of various benzylamines, exclusively forming imine products. These reactions are conducted under very mild conditions, without the addition of any additives, yielding excellent selectivities and high yields of secondary imines in a green manner by minimizing wastes.

Efficient and chemoselective hydrogenation of aldehydes catalyzed by well-defined PN3-pincer manganese(II) catalyst precursors: an application in furfural conversion.

Well-defined and air-stable PN3-pincer manganese(II) complexes were synthesized and used for the hydrogenation of aldehydes into alcohols under mild conditions using MeOH as a solvent. This protocol is applicable for a wide range of aldehydes containing various functional groups. Importantly, α,ß-unsaturated aldehydes, including ynals, are hydrogenated with the CC double bond/CC triple bond intact. Our methodology was demonstrated for the conversion of biomass derived feedstocks such as furfural and 5-formylfurfural to furfuryl alcohol and 5-(hydroxymethyl)furfuryl alcohol respectively.

Heterogeneous hydrosilylation reaction catalysed by platinum complexes immobilized on bipyridine-periodic mesoporous organosilicas.

The utility of a bipyridine periodic mesoporous organosilica, BPy-PMO, as a support material of a hydrosilylation catalyst was investigated in the hydrosilylation of phenylacetylene with trimethoxysilane. [PtMe2(BPy-PMO)] (1) exhibited a moderate catalytic activity, whereas the reaction was successfully catalysed by [PtMe2(BPy-PMO-TMS)] (2) bearing end-capped TMS groups on the surface. Spectroscopic analyses of 2 revealed that the porous structure of BPy-PMO-TMS remained almost unchanged through the reaction. The hot filtration test supported the nonleaching property of 2, thereby exhibiting good reusability without the loss of the product yields.

Cobalt-Catalyzed Selective Hydrogenation of Nitriles to Secondary Imines.

The first example of cobalt-catalyzed selective hydrogenation of nitriles to secondary imines is reported. The results demonstrate the significantly different selectivity compared with the previously reported cobalt catalytic system during the nitrile hydrogenation. A variety of aromatic and aliphatic nitriles are hydrogenated to the corresponding secondary imines.