Cationic Iridium-Catalyzed Decarboxylation of Aromatic Carboxylic Acids.

Practical synthetic applications of catalytic decarboxylation in producing useful molecules are limited. We report herein the cationic Ir-catalyzed decarboxylations of various electron-rich and -poor aromatic carboxylic acids to produce hydrocarbons in good yield (up to >99%). Additionally, this reaction is applicable in decarboxylative hydroarylation of bicyclic alkenes and decarboxylative fluorination, indicating the potential utility of this catalytic decarboxylation in synthetic chemistry.

Cationic Iridium-Catalyzed Asymmetric Decarbonylative Aryl Addition of Aromatic Aldehydes to Bicyclic Alkenes.

Invited for the cover of this issue are Tomohiko Shirai and co-workers at the National Institute of Technology Kochi College and their collaborators at Chuo and Hokkaido Universities. The image depicts how asymmetric decarbonylative C-C bond formation by the Ir/S-Me-BIPAM complex takes precedence over aldehyde decarbonylation. Read the full text of the article at 10.1002/chem.202104347.

Cationic Iridium-Catalyzed Asymmetric Decarbonylative Aryl Addition of Aromatic Aldehydes to Bicyclic Alkenes.

We report an unprecedented catalytic protocol for the enantioselective decarbonylative transformation of aryl aldehydes. In this process, the decarbonylation of aldehydes catalyzed by chiral iridium complexes enabled the formation of asymmetric C-C bonds through the formation of an aryl-iridium intermediate. The decarbonylative aryl addition to bicyclic alkenes was fluidly performed without a stoichiometric aryl-metal reagent, such as aryl boronic acid, with a cationic iridium complex generated in situ from Ir(cod)2 (BArF 4 ) and the sulfur-linked bis(phosphoramidite) ligand ((R,R)-S-Me-BIPAM). This reaction has broad functional group compatibility, and no waste is generated, except carbon monoxide.

Cationic Iridium/Chiral Bisphosphine-Catalyzed Enantioselective Hydroacylation of Ketones.

A facile and convenient synthesis of the chiral phthalide framework catalyzed by cationic iridium was developed. The method utilized cationic iridium/bisphosphine-catalyzed asymmetric intramolecular carbonyl hydroacylation of 2-keto benzaldehydes to furnish the corresponding optically active phthalide products in good to excellent enantioselectivities (up to 98% ee). The mechanistic studies using a deuterium-labelled substrate suggested that the reaction involved an intramolecular carbonyl insertion mechanism to iridium hydride intermediate. In addition, we investigated the kinetic isotope effect (KIE) of intramolecular hydroacylation with deuterated substrate and determined that the C-H activation step is not included in the turnover-limiting step.

Rhodium-Catalyzed Enantioselective Arylation of Aliphatic Imines.

Chiral rhodium(I)-catalyzed highly enantioselective arylation of aliphatic N-sulfonyl aldimines with arylboronic acids has been developed. This transformation is achieved by the use of a rhodium/bis(phosphoramidite) catalyst to give enantiomerically enriched α-branched amines (up to 99 % ee). In addition, this system enables efficient synthesis of (+)-NPS R-568 and Cinacalcet which are calcimimetic agents.

Cationic Iridium/S-Me-BIPAM-Catalyzed Direct Asymmetric Intermolecular Hydroarylation of Bicycloalkenes.

Highly enantioselective cationic iridium-catalyzed hydroarylation of bicycloalkenes, by carbonyl-directed C-H bond cleavage, was accomplished using a newly synthesized sulfur-linked bis(phosphoramidite) ligand (S-Me-BIPAM). The reaction provides alkylated acetophenone or benzamide derivatives in moderate to excellent yields and good to excellent enantioselectivities. Notably, the hydroarylation reaction of 2-norbornene with N,N-dialkylbenzamide proceeds with excellent enantioselectivity (up to 99% ee) and high selectivity for the mono-ortho-alkylation product.

Cationic Ir/Me-BIPAM-catalyzed asymmetric intramolecular direct hydroarylation of α-ketoamides.

Asymmetric intramolecular direct hydroarylation of α-ketoamides gives various types of optically active 3-substituted 3-hydroxy-2-oxindoles in high yields with complete regioselectivity and high enantioselectivities (84-98% ee). This is realized by the use of the cationic iridium complex [Ir(cod)2](BAr(F)4) and the chiral O-linked bidentate phosphoramidite (R,R)-Me-BIPAM.

Me-BIPAM for the synthesis of optically active 3-aryl-3-hydroxy-2-oxindoles by ruthenium-catalyzed addition of arylboronic acids to isatins.

A chiral O-linked C(2)-symmetric bidentate phosphoramidite (Me-BIPAM) was found to be efficient for the ruthenium-catalyzed addition of arylboronic acids to isatins. Asymmetric synthesis of 3-aryl-3-hydroxy-2-oxindoles by 1,2-addition of arylboronic acids to isatins was carried out in the presence of [RuCl(2)(PPh(3))(3)]/(R,R)-Me-BIPAM and KF, resulting in an enantioselectivity as high as 90 % ee. It was found that the reaction with N-protected isatins proceeds with high yields and good enantioselectivities. The best protective groups on the nitrogen atom were different depending on the substituents on the aromatic ring. The use of a N-benzyl group resulted in excellent enantioselectivities in many substrates compared with other groups.

Asymmetric addition of arylboronic acids to glyoxylate catalyzed by a ruthenium/Me-BIPAM complex.

The enantioselective synthesis of α-hydroxy esters by ruthenium-catalyzed 1,2-addition of arylboronic acids to tert-butyl glyoxylate is described. The use of RuCl(2)(PPh(3))(3) with (R,R)-Me-BIPAM gave optically active mandelic acids of up to 99% ee. Addition of a fluoride salt such as potassium fluoride (KF) or caesium fluoride (CsF) was effective for achieving high enantioselectivities.

Ru/Me-BIPAM-catalyzed asymmetric addition of arylboronic acids to aliphatic aldehydes and α-ketoesters.

A ruthenium-catalyzed asymmetric arylation of aliphatic aldehydes and α-ketoesters with arylboronic acids has been developed, giving chiral alkyl(aryl)methanols and α-hydroxy esters in good yields. The use of a chiral bidentate phosphoramidite ligand (Me-BIPAM) achieved excellent enantioselectivities.

Rhodium-catalyzed 1,4-addition of lithium 2-furyltriolborates to unsaturated ketones and esters for enantioselective synthesis of γ-oxo-carboxylic acids by oxidation of the furyl ring with ozone.

Rhodium-catalyzed 1,4-addition of lithium 5-methyl-2-furyltriolborate ([ArB(OCH(2))(3)CCH(3)]Li, Ar = 5-methyl-2-furyl) to unsaturated ketones to give ß-furyl ketones was followed by ozonolysis of the furyl ring for enantioselective synthesis of γ-oxo-carboxylic acids. [Rh(nbd)(2)]BF(4) (nbd = 2,5-norbornadiene) chelated with 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap) or 2,3-bis(diphenylphosphino)butane (chiraphos) gave high yields and high selectivities in a range of 91-99% ee at 30 °C in a basic dioxane/water solution. The corresponding reaction of unsaturated esters, such as methyl crotonate, had strong resistance under analogous conditions, but the 1,4-adduct was obtained in 70% yield and with 94% ee when more electron-deficient phenyl crotonate was used as the substrate.