Tuning the Chemoselectivity of Silyl Protected Rhamnals by Temperature and Brønsted Acidity: Kinetically Controlled 1,2-Addition vs Thermodynamically Controlled Ferrier Rearrangement

Abstract

An acidity-and temperature-dependent chemoselective glycosylation of silyl-protected rhamnals with alcohols has been revealed. The reaction undergoes a 1,2-addition pathway with (±)-CSA as the catalyst at rt, affording kinetically controlled 2-deoxyl rhamnosides. In contrast, only thermodynamically controlled 2,3-unsaturated rhamnosides are formed via Ferrier rearrangement when elevating reaction temperature to 85 °C or using CF 3 SO 3 H instead. This tunable glycosylation allows facile and practical access to both 2-deoxyl and 2,3-unsaturated rhamnosides with excellent yields and high αstereoselectivity.

Electrochemical Bromination of Glycals

“…The reaction of 3h with potassium phenyltrifluoroborate 4b also proceeded smoothly to provide the corresponding product 5b in 79% yield ( Molander and Fumagalli, 2006 ). Moreover, disaccharide 5c was successfully synthesized in the promotion of BF 3 ·Et 2 O in 72% yield with excellent α-selectivity via the Ferrier rearrangement reaction ( Dharuman et al, 2013 ; Wang et al, 2019 ).…”

Directed Nickel‐Catalyzed pseudo‐Anomeric C−H Alkynylation of Glycals as an Approach towards C‐Glycoconjugate Synthesis

“…2‐ N ‐(quinolin‐8‐yl)carbamoyl‐1‐((triisopropylsilyl)ethynyl)‐3,4‐ O ‐benzyl‐ l ‐rhamnal (5 a) . 3,4‐di‐ O ‐benzyl‐ l ‐rhamnal was prepared according to the literature [20] . 2‐Iodo‐3,4‐di‐ O ‐benzyl‐ l ‐rhamnal ( S1 ) was synthesized following the described procedure: [18] 3,4‐di‐ O ‐benzyl‐ l ‐rhamnal (1 g, 1 equiv., 3.22 mmol) was dissolved in dry acetonitrile (22 mL) under argon and the resulting mixture was heated to 80 °C.…”

PdCl2/CuCl2/Bi(OTf)3‐promoted Construction of Sulfonyl Dibenzooxabicyclo[3.3.1]nonanes and Arylnaphthalenes via Intramolecular Annulation of Sulfonyl o‐Allylarylchromanones

“…Among these diverse kinds of reaction routes, a number of synthetic efforts have attempted to control one factor or variant to generate different products with approximate or distinct skeletons in recent reports. These adjusting factors included temperature, [1][2][3][4][5][6][7][8][9][10][11][12][13][14] catalyst, [15][16][17][18][19][20][21] additive (e. g. ligand, [22][23][24][25] base [26][27] and reagent [28][29][30][31] ) and solvent. [32][33][34][35] On the basis of the abovementioned investigations, we found that controlling the temperature change is a simple, economical and direct protocol for affecting the formation of different products in comparison with other variables.…”

“…Yield = 85% (179 mg); Colorless gum; HRMS (ESI-TOF) m/z: [M + H] + calcd for C 24 H 21 O 5 S 421.1110, found 421.1113; NMR (400 MHz, CDCl 3 ): δ 8.95 (s, 1H), 7.94 (s, 1H), 7.86 (d, J = 8.8 Hz, 1H), 7.46 (d, J = 8.8 Hz, 1H), 7.40 (dt, J = 2.0, 7.6 Hz, 1H), 7.29-7.18 (m, 5H), 6.91 (dd, J = 0.8, 8.0 Hz, 1H), FULL PAPER asc.wiley-vch.de6.70 (dt, J = 0.8, 8.0 Hz, 1H),6.54 (dd, J = 0.8, 7.6 Hz, 1H), 5.47 (br s, 1H), 4.03 (s, 3H), 3.91 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ 153.7, 151.3, 142.5, 139.8, 135.3, 132.7, 132.2, 131.7, 130.8, 130.7, 130.1, 129.7, 128.4 (2x), 128.2, 127.6 (2x), 126.5, 125.9, 120.3, 117.6, 116.5, 61.1, 56.6.2-(3-Methanesulfonyl-7,8-dimethoxynaphthalen-2-yl)phenol (7 c). Yield = 80% (143 mg); Colorless gum; HRMS (ESI-TOF) m/z: [M + H] + calcd for C 19 H 19 O 5 S 359.0953, found 359.0957; NMR (400 MHz, CDCl 3 ): δ 8.71 (s, 1H), 8.07 (s, 1H), 7.82 (d, J = 8.8 Hz, 1H), 7.46 (d, J = 8.8 Hz, 1H), 7.40 (dt, J = 2.0, 7.6 Hz, 1H), 7.27 (dd, J = 2.0, 7.6 Hz, 1H), 7.10 (dd, J = 0.8, 8.0 Hz, 1H), 7.07 (dt, J = 0.8, 8.0 Hz, 1H), 5.69 (br s, 1H), 4.05 (s, 3H), 3.96 (s, 3H), 2.82 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ 153.7, 151.4, 142.6, 135.0, 131.9, 131.7, 130.9, 130.7, 130.6, 127.9, 127.1, 126.6, 126.0, 121.1, 118.8, 116.6, 61.3, 56.6, 43.0.…”