Regioselective Benzoylation of Diols and Carbohydrates by Catalytic Amounts of Organobase

Abstract

Abstract:A novel metal-free organobase-catalyzed regioselective benzoylation of diols and carbohydrates has been developed. Treatment of diol and carbohydrate substrates with 1.1 equiv. of 1-benzoylimidazole and 0.2 equiv. of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN under mild conditions resulted in highly regioselective benzoylation for the primary hydroxyl group. Importantly, compared to most commonly used protecting bulky groups for primary hydroxyl groups, the benzoyl protective group offers a new protection strategy.

Regio/Stereoselective Glycosylation of Diol and Polyol Acceptors in Efficient Synthesis of Neu5Ac‐α‐2,3‐LacNPhth Trisaccharide

“…The reactions were carriedo ut in dichloromethane in the presence of 4 molecular sieves.M oderate yield of LacNPhth product 6a (71 %) was obtained due to the formation of orthoester 7 (15 %) even under the optimized condition (See in supporting information,T able S1). Subsequently,t he phenyl6 -O-benzoyl-2-deoxy-2-phthalimido-1-thio-b-d-glucopyranoside 5j,s ynthesized via regioselective benzoylation in 89 %y ield starting from phenyl 2-deoxy-2-phthalimido-1-thiob-d-glucopyranoside, [10] was chosen as the acceptort or eact with the donor 4a.U nder the optimized condition (Entry 12 in Ta ble 1. 0.1 equiv of TMSOTf, À20 8C), LacNPhth product 6b was isolated in 69 %y ield (optimizationsi nt he Supporting Information,T able S1).…”

Catalyst Free Selective Monobenzoylation of Diols with Benzoyl Cyanide: A Robust and Regioselective Strategy

“…Recently, a regioselective axial hydroxyl group benzoylation in carbohydrate scaffolds was achieved with cyanide effect . In addition, benzoylimidazole in the presence of organic bases was also utilized to perform selective benzoylation of polyols, however, a general and environment‐friendly approach towards this direction is still lacking. Though in recent past deep eutectic solvents were utilized to achieve the acylation reaction of alcohols under green conditions, however, their applicability was limited to a particular class of hydroxyl group functionality .…”

Stereospecific β‐l‐Rhamnopyranosylation through an SNi‐Type Mechanism by Using Organoboron Reagents

“…However, b-l-Rhap-(1,4) substructures linking to Glc and GlcNAc residues also have been found in some pathogenic bacterial polysaccharides. Initially, 44 was prepared by regioselective benzoylation [20] of 40,which was synthesized by the present glycosylation of 6 and 35 using 39 (Table 3). Based on apreviously reported predictive model for regioselectivity of boronic acid catalyzed glycosylations (see Figure S1 in the Supporting Information), glycosylations at the 4p osition are kinetically more favorable.G lycosylations of 35-38 with 6 using ac atalytic amount of 39 in MeCN at room temperature or 0 8 8Cfor 6hproceeded smoothly to give the corresponding b-l-rhamnosides 40-43 in high yield with complete b-stereoselectivity (Table 3), which demonstrates that boronic acid catalyzed regioselective glycosylation can be used to produce several b-l-Rhap-(1,4) structures in high yield with complete stereoselectivity.…”

“…Finally,t he synthesis of the trisaccharide a-l-Rhap-(1,2)b-l-Rhap-(1,4)-Glcp,w hich is derived from S. pneumoniae serotypes 7B,7C, and 7D,was examined (Scheme 2). Initially, 44 was prepared by regioselective benzoylation [20] of 40,which was synthesized by the present glycosylation of 6 and 35 using 39 (Table 3). Subsequent a-l-rhamnosylation of 44 with 45 cleanly afforded the desired trisaccharide 46 in high yield as asingle isomer.…”