A synergistic Rh(I)/organoboron-catalysed site-selective carbohydrate functionalization that involves multiple stereocontrol

Abstract

Site-selective functionalization is a core synthetic strategy that has broad implications in organic synthesis. Particularly, exploiting chiral catalysis to control site selectivity in complex carbohydrate functionalizations has emerged as a leading method to unravel unprecedented routes into biologically relevant glycosides. However, robust catalytic systems available to overcome multiple facets of stereoselectivity challenges to this end still remain scarce. Here we report a synergistic chiral Rh(I)- and organoboron-catalysed protocol, which enables access into synthetically challenging but biologically relevant arylnaphthalene glycosides. Our method depicts the employment of chiral Rh(I) catalysis in site-selective carbohydrate functionalization and showcases the utility of boronic acid as a compatible co-catalyst. Crucial to the success of our method is the judicious choice of a suitable organoboron catalyst. We also determine that exquisite multiple aspects of stereocontrol, including enantio-, diastereo-, regio- and anomeric control and dynamic kinetic resolution, are concomitantly operative.

Synthesis of a C2-Symmetric Chiral Borinic Acid and Its Application in Catalytic Desymmetrization of 2,2-Disubstituted-1,3-Propanediols

“…According to these results and references, − we postulated that the reaction proceeded via the borate ion as the key intermediate and we also proposed a stereocontrol model to explain the results of the reaction. From the intermediate, due to the change of sp 2 B to sp 3 B, the oxabora-anthracene folds somewhat in order to meet the requirement of the tetrahedral structure (Figure ).…”

“…It has also been proven to be an excellent activator of alcohols via its covalent interactions with hydroxyl groups, and particularly as a molecular probe that is useful in recognition and identification of sugars . At the same time, application of boronic acids as catalysts in activation of alcohols and carboxylic acids has received considerable attention. , In contrast, the highly catalytic enantioselective processes catalyzed by chiral boronic acid have lagged behind and remain a challenging task due to the extreme lack of an efficient chiral boronic acid. , …”

Boronic Acid/Palladium Hybrid Catalysis for Regioselective O-Allylation of Carbohydrates

“…. 16 This compound was synthesized according to general procedure A, from methyl 6-O-(tert-butyldimethylsilyl)-α-D-mannopyranoside (2a) 3a (61.7 mg, 0.200 mmol, 1.0 equiv) for 1.5 h. The yields of regioisomer were determined by 1 H NMR analysis of the crude product mixture using p-xylene as an internal standard (93% of 4a and 7% of 5, 4a/5 = 13:1). The resulting crude material was purified by silica gel chromatography (4:1 n-hexane/EtOAc) to give 4a (63.4 mg, 0.182 mmol, 91%) as a colorless oil.…”

“…. 16 This compound was synthesized according to general procedure A, from methyl 6-O-(tert-butyldimethylsilyl)-α-D-galactopyranoside (2e) 3a (61.7 mg, 0.200 mmol, 1.0 equiv) for 2 h. The resulting crude material was purified by silica gel chromatography (2:1 n-hexane/EtOAc) to give 4e (67.6 mg, 0.194 mmol, 97%) as a white solid. Data for 4e: R f = 0.23 (2:1 n-hexane/EtOAc); 1 H NMR (400 MHz, CDCl 3 ): δ 5.95 (ddt, J = 17.2, 10.4, 6.0 Hz, 1H), 5.31 (dq, J = 17.2, 1.6 Hz, 1H), 5.20 (dq, J = 10.4, 1.6 Hz, 1H), 4.81 (d, J = 4.0 Hz, 1H, H-1), 4.21 (ddt, J = 13.2, 6.0, 1.6 Hz, 1H), 4.17 (ddt, J = 13.2, 6.0, 1.6 Hz, 1H), 4.10 (dd, J = 3.6, 1.2 Hz, 1H, H-4), 3.95 (dd, J = 9.6, 4.0 Hz, 1H, H-2), 3.88 (dd, J = 10.0, 5.6 Hz, 1H, H-6), 3.80 (dd, J = 10.0, 5.6 Hz, 1H, H-6), 3.72 (dt, J = 5.6 Hz, 1.2 Hz 1H, H-5), 3.53 (dd, J = 9.6, 3.6 Hz, 1H, H-3), 3.41 (s, 3H), 2.61 (br, 1H, OH), 2.12 (br, 1H, OH), 0.89 (s, 9H), 0.08 (s, 6H); 13…”

Stable and efficient planar Cu/Cu2O film catalysts

“…Catalysis phenomena are ubiquitous and involve almost all fields of chemical reaction processes since a lot of new molecules and substances can be designed and created. [1][2][3][4][5][6] Generally, particle-shaped catalysts are widely used in solution chemical synthesis to reduce the reaction activation energy due to their larger surface area, good catalysis performance and the ability to alter the chemical reaction pathway, which will robustly accelerate chemical reactions and enable the molecular reaction to be tailored rationally for desired atom combination and connection via chemical bonding. [7][8][9][10][11][12][13] In most cases, powdered materials are commonly used as catalysts, which need to be separated through centrifugation or filtration after a solution reaction is fully completed; however, in a solid reaction, separating the catalyst from the reaction system remains difficult due to low separation efficiency, [14][15][16][17][18][19][20][21][22] thus a method for removing the catalysts simply and efficiently from reaction systems is urgently needed, especially for valuable or toxic catalysts.…”