Functionalized flower-like mesoporous silica with a chiral organorhodium functionality incorporated within its silica framework is prepared through an assembly of chiral 4-((trimethoxysilyl)ethyl)phenylsulfonyl-1,2-diphenylethylenediamine and tetraethoxysilane under a cooperative dual-template approach followed by complexation with organorhodium complexes. Structural characterization discloses its mesostructure and well-defined single-site chiral organorhodium functionality, while electron microscopy analyses reveal the uniformly distributed three-dimensional spherical flowers constructed by the stacking of leaf-shaped nanoflakes. In particular, as a bifunctionalized heterogeneous catalyst, it shows excellent catalytic activity and high enantioselectivity in the asymmetric transfer hydrogenation of aromatic ketones in aqueous medium (more than 99% conversion and up to 97% ee). The superior catalytic performance is attributed to the synergistic effect of the salient cetyltrimethylammonium bromide phasetransfer function and confined chiral organorhodium catalytic nature. Furthermore, this heterogeneous catalyst could be recovered easily and reused repeatedly (ten times) without affecting its ee value, showing a practical application in asymmetric synthesis. † Electronic supplementary information (ESI) available. See
The facile construction of biologically active b-adrenergic receptor agonists/blockers and analoguesi sag reat fundamental and practical challenge in medicalc hemistry.H erein, we report ah ydration-asymmetric transfer hydrogenation cascade to realize the one-pot enantioselective transformation of aromatic haloalkynes into chiral aromatic halohydrins, which can be converted readily into chiral b-adrenergicreceptor blockers. Such ao ne-pot cascade process involves the Au-catalyzed hydration of aryl-substituted haloalkynes to aryl-substituted a-halomethyl ketones and the Ru-catalyzeda symmetric transfer hydrogenation of aryl-substituted a-halomethyl ketones to aryl-substituted 2-haloethanols. The significant benefits of this procedure are that it provides chiral aromatic halohydrins in high yields, with excellent enantioselectivities,a nd aw ide variety of functional groups are tolerated under mild conditions. Thes tudy described herein offers au seful approach to construct chiral badrenergic blockers, whichi sa na ttractive practical organic transformation that is performed in ao ne-pot manner.Opticallyp ure halohydrins, especially aryl-substituted 2-haloethanols as important synthetic motifs, have attracted great interest in medical chemistry. [1] Great achievements through the utilization of aryl-substituted 2-haloethanols as building blocks are well documented, as these building blocks can be readily converted into various b-adrenergicr eceptor agonists and blockers. [2] As shown in Figure1,s ome prominent examples, such as nifenalol [2a, b] and pronethalol, [2b] are important medicines as b-adrenergicr eceptor blockers, whereas metaproterenol [2c] and fenoterol [2d] are b-adrenergicr eceptor agonists. Generally,t he construction of aryl-substituted 2-haloethanols can be performed through two single-step reactions, in which hydration of haloalkynes gives a-halomethyl ketones and asymmetric transformation of the a-halomethyl ketones provides 2haloethanols. Owing to the demands of atom economy and minimal workup procedures, the facile construction of aryl-sub-stituted2 -haloethanols followed by their transformation into biologically active b-adrenergicr eceptor agonists or blockers is highly desirable.One-pot cascade reactions are atom economical, and they are well known to construct various valuablec ompounds with minimum isolation/purification processes. [3] As two classical reactions for the construction of aryl-substituted 2-haloethanols, the hydration of a-haloalkynes to 2-haloketones [4] andt he asymmetrict ransfer hydrogenation (ATH) of 2-haloketones to chiral 2-haloethanols [5] have been extensively studied theoretically and practically.H owever,t he one-pot directt ransformation of alkynes into alcohols through ac ascade process is still an unmet challenge, [6] and this can be mainly ascribed to complicated conflicts derived from intrinsic bimetallic incompatibility ande xtrinsic reaction conditions. So far,o nly one successful example of the one-pot enantioselective transformation of alkynes in...
Dynamic kinetic resolution of phthalides through asymmetric transfer hydrogenation for the construction of 3-(2-hydroxy-2-arylethyl)isobenzofuran-1(3H)-one with 1,3-distereocenters has been developed. This procedure is carried out under a mild condition at 40 °C catalyzed with RuCl[(S,S)-TsDPEN](mesitylene) using HCOOH/Et3N (5:2) as a hydrogen source. A variety of phthalides are smoothly transferred to provide optically pure phthalides with high yields, excellent enantioselectivities, and acceptable diastereomeric ratios.
One-Pot Cascade Hydration-Asymmetric Transfer Hydrogenation as a Practical Strategy to Construct Chiral -Adrenergic Receptor Blockers. -The title process allows for the conversion of aryl-substituted haloalkynes into chiral halohydrins, useful precursors for the preparation of -andrenergic receptor blockers. -(YE, Q.; CHENG*, T.; ZHAO, Y.; ZHAO, J.; JIN, R.; LIU, G.; ChemCatChem 7 (2015) 12, 1801-1805, http://dx.
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