108673-17-2Relevant articles and documents
Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines
Landwehr, Anne,Dudle, Balz,Fox, Thomas,Blacque, Olivier,Berke, Heinz
, p. 5701 - 5714 (2012)
The silyloxycyclopentadienyl hydride complexes [Re(H)(NO)(PR 3)(C5H4OSiMe2tBu)] (R=iPr (3a), Cy (3b)) were obtained by the reaction of [Re(H)(Br)(NO)(PR3) 2] (R=iPr, Cy) with Li[C5H4OSiMe 2tBu]. The ligand-metal bifunctional rhenium catalysts [Re(H)(NO)(PR3)(C5H4OH)] (R=iPr (5a), Cy (5b)) were prepared from compounds 3a and 3b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts [Re(H)(NO)(PR 3)(C5H4O)][NBu4] (R=iPr (4a), Cy (4b)) with NH4Br. In nonpolar solvents, compounds 5a and 5b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species [Re(H)2(NO)(PR3)(C5H4O)] (6a,b). Deuterium-labeling studies of compounds 5a and 5b with D2 and D 2O showed H/D exchange at the HRe and HO positions. Compounds 5a and 5b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H2 source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones. The Re-al deal: Bifunctional rhenium complexes [Re(H)(NO)(PR 3)(C5H4OH)] (R=Cy, iPr) of Shvo-type were prepared and used as catalysts for the transfer hydrogenation of ketones and imines. TOFs up to 1164 h-1 were obtained for ketones and up to 79 h-1 for imines. DFT calculations suggested a secondary-coordination- sphere mechanism for the transfer hydrogenation of ketones.
The Stereoselective Oxidation of para-Substituted Benzenes by a Cytochrome P450 Biocatalyst
Chao, Rebecca R.,Lau, Ian C.-K.,Coleman, Tom,Churchman, Luke R.,Child, Stella A.,Lee, Joel H. Z.,Bruning, John B.,De Voss, James J.,Bell, Stephen G.
supporting information, p. 14765 - 14777 (2021/09/14)
The serine 244 to aspartate (S244D) variant of the cytochrome P450 enzyme CYP199A4 was used to expand its substrate range beyond benzoic acids. Substrates, in which the carboxylate group of the benzoic acid moiety is replaced were oxidised with high activity by the S244D mutant (product formation rates >60 nmol.(nmol-CYP)?1.min?1) and with total turnover numbers of up to 20,000. Ethyl α-hydroxylation was more rapid than methyl oxidation, styrene epoxidation and S-oxidation. The S244D mutant catalysed the ethyl hydroxylation, epoxidation and sulfoxidation reactions with an excess of one stereoisomer (in some instances up to >98 %). The crystal structure of 4-methoxybenzoic acid-bound CYP199A4 S244D showed that the active site architecture and the substrate orientation were similar to that of the WT enzyme. Overall, this work demonstrates that CYP199A4 can catalyse the stereoselective hydroxylation, epoxidation or sulfoxidation of substituted benzene substrates under mild conditions resulting in more sustainable transformations using this heme monooxygenase enzyme.
Asymmetric Hydrogenation of Ketones and Enones with Chiral Lewis Base Derived Frustrated Lewis Pairs
Du, Haifeng,Feng, Xiangqing,Gao, Bochao,Meng, Wei
supporting information, p. 4498 - 4504 (2020/02/05)
The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal-free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner.
