STEREOSELECTIVE SYNTHESIS OF PSEUDOGLYCAL C-GLYCOSIDES VIA TRICHLOROACETIMIDATE ACTIVATION OF GLYCALS^a

Abstract

Dedicated to Prof. Joachim Thiem on the occasion of his 60th birthday. ABSTRACTA variety of functionalized pseudoglycal C-glycosides (C-pseudoglycals or C-hex-2-enopyranosides) have been obtained in excellent yield and stereoselectivity from the trimethylsilyl triflate (Me 3 SiOTf) catalyzed reaction of trichloroacetimidate derivative 2 with silylated nucleophiles such as allyl and propargyl silanes and silyl enol ethers.

Recent Advances in the Chemical Synthesis of C-Glycosides

“…Reactions of glycals with silylated C -nucleophiles under the influence of various promoters provide 2,3-unsaturated sugars through Ferrier rearrangement with the α-anomers as the predominant products (Table ). − Thus, coupling of peracetylated glucal 143 with silylated nucleophiles such as allylsilane, propargylsilane, and silyl enol ether promoted by ytterbium­(III) triflate [Yb­(OTf) 3 ] produced C -pseudoglycals 151 – 155 in good yields (88–94%) and excellent α-selectivities (from α/β = 5:1 to α only). , In the presence of iodide, glycals 143 and 146 reacted with allylsilane and silyl cyanide to give 2,3-unsaturated glycosides 151 and 156 – 158 in high yields with the α-anomers as the major products. , InCl 3 -catalyzed glycosylation of various glycals ( 143 , 146 , 147 ) with allylsilane and silyl cyanide under microwave conditions afforded α- C -allyl glycosides ( 151 , 157 , 159 ) as the predominant anomers and α- C -cyanides ( 156 , 158 , 160 ) with moderate selectivities. , Use of the bismuth­(III), thulium­(III), and gadolinium­(III) triflates [Bi­(OTf) 3 , Tm­(OTf) 3 , and Gd­(OTf) 3 , respectively] as the promoters for similar reactions provided the corresponding C -glycosides ( 151 , 154 , 156 – 158 , 161 ) in good yields with high α-selectivities. − Likewise, coupling using HClO 4 ·SiO 2 as the catalyst yielded the α- C -glycosides ( 151 , 156 , 162 ) as the major products (62–90%, α/β = 2:1–20:1) …”

“…Similarly, the AuCl 3 -catalyzed Ferrier reactions of glycals 143 , 146 , and 149 with allylsilane led to 2,3-unsaturated C -glycosides 151 , 157 , and 166 with the α-anomers as the major products . Trimethylsilyl triflate- (TMSOTf-) promoted glycosylation of galactal 3- O -trichloroacetimidate 150 with allylsilanes, propargylsilane, and silyl enol ethers furnished α- C -glycosides 167 – 171 in excellent yields . Coupling of glucal 143 with difluoroenoxysilanes under the promotion of BF 3 ·OEt 2 afforded difluoro- C -glycosides 172 – 175 in satisfactory yields with the α-anomers as the major products. − …”

Phthalimidomethylation ofO-Nucleophiles withO-Phthalimidomethyl Trichloroacetimidate:A Powerful Imidomethylating Agent forO-Protection

“…17 The phthalimidomethyl derivatives have been used for the identification [18][19][20][21][22] of amines and alcohols via nucleophilic substitution 23 of a leaving group on the Pim moiety. The biological activities as well as our interest in the reactivity of trichloroacetimidates [24][25][26][27] attracted our attention to develop a method for introducing the phthalimidomethyl group on nucleophiles to form, for instance, CO bonds under acid catalysis. O-Phthalimidomethyl trichloroacetimidate (2) (Scheme 1) was expected to serve as an imidomethylating agent; ensuing removal of the phthaloyl residue in the products will readily provide the corresponding aminomethyl derivatives.…”