RESUMEN
The Rh(I)-catalyzed direct reorganization of organic frameworks and group exchanges between carboxylic acids and aryl ketones was developed with the assistance of directing group. Biaryls, alkenylarenes, and alkylarenes were produced in high efficiency from aryl ketones and the corresponding carboxylic acids by releasing the other molecule of carboxylic acids and carbon monoxide. A wide range of functional groups were well compatible. The exchanges between two partners were proposed to take place on the Rh-(III) center of key intermediates, supported by experimental mechanistic studies and computational calculations. The transformation unveiled the new catalytic pathway of the group transfer of two organic molecules.
Asunto(s)
Carbono/química , Ácidos Carboxílicos/química , Cetonas/química , Compuestos Organometálicos/química , Rodio/química , Catálisis , Estructura MolecularRESUMEN
We report three transformations: 1)â direct transformation from biarylmethanols into biarylmethylamines; 2)â direct transformation from one biarylmethanol into another biarylmethanol; 3)â direct transformation from allylic alcohols into allylic amines. These transformations are based on pyridyl-directed Rh-catalyzed C-C bond cleavage of secondary alcohols and subsequent addition to C=X (X = N or O) double bonds. The reaction conditions are simple and no additive is required. The driving force of C-C bond cleavage is the formation of the stable rhodacycle intermediate. Other directing groups, such as the pyrazolyl group, can also be used although it is not as efficient as the pyridyl group. We carried out in-depth investigations for transformation 1 and found that: 1)â the substrate scope was broad and electron-rich alcohols and electron-deficient imines are more efficient; 2)â as the leaving group, aldehyde had no significant impact on either the C-C bond cleavage or the whole transformation; 3)â mechanistic studies (intermediate isolation, in situ NMR spectroscopic studies, competing reactions, isotopic labeling experiments) implied that: i)â The C-C cleavage was very efficient under these conditions; ii)â there is an equilibrium between the rhodacycle intermediate and the protonated byproduct phenylpyridine; iii)â the addition step of the rhodacycle intermediate to imines was slower than the C-C cleavage and the equilibrium between the rhodacycle and phenylpyridine; iv)â the whole transformation was a combination of two sequences of C-C cleavage/nucleophilic addition and C-C cleavage/protonation/C-H activation/nucleophilic addition, with the latter being perhaps the main pathway. We also demonstrated the first example of cleavage of an C(alkenyl)-C(benzyl) bond. These transformations showed the exchange (or substitution) of the alcohol group with either an amine or another alcohol group. Like the "group transplant", this method offers a new concept that can be used to directly synthesize the desired products from other chemicals through reorganization of carbon skeletons.
Asunto(s)
Aldehídos/química , Aminas/química , Compuestos de Bencilo/química , Propanoles/química , Rodio/química , Alcoholes , Catálisis , Hidrogenación , Estructura Molecular , EstereoisomerismoRESUMEN
Cutting loose: 1,1-Biarylmethanol substrates undergo reductive cleavage of the C-C bond in the presence of a cationic Rh(III) catalyst and H(2) (see scheme; DG=directing group). Various functional groups are tolerated in the reaction system. Preliminary studies indicate that a five-membered rhodacycle intermediate, which then converts into a Rh(III) hydride species for the reduction, is involved in the catalytic cycle.
Asunto(s)
Alcoholes Bencílicos/química , Rodio/química , Catálisis , Hidrogenación , Metanol/análogos & derivados , Oxidación-ReducciónRESUMEN
Snipping tool: the rhodium(I)-catalyzed extrusion of carbon monoxide from biaryl ketones and alkyl/alkenyl aryl ketones was developed to produce biaryls and alkyl/alkenyl arenes, respectively, in high yields. A wide range of functionalities are tolerated. Not only does this method provide an alternative pathway to construct useful scaffolds, but also offers a new strategy for C-C bond activation.