Glycoside Synthesis from 1‐Oxygen Substituted Glycosyl Donors: Sections 3.1 and 3.2

A high-yielding synthesis of allyl glycosides from peracetylated glycosyl donors

“…Easily accessible glycosyl donors suitable for this purpose are the peracetylated -configured glucose and galactose derivatives ( 7 and 8 ), which can be activated with inexpensive Lewis acids such as boron trifluoride etherate or trimethylsilyltriflouromethane sulfonate (TMSOTf), but other Lewis acid promoters, e.g., zinc chloride, tin tetrachloride and tin tetrachloride/silver acetate mixtures have also been used. [7] Depending on the reaction conditions certain Lewis acids can also produce predominantly -glycosides via acid catalyzed anomerization. [7c,d] While there are reports of high glycosylation yields and good stereocontrol achievable with peracetylated donors, in particular for the synthesis of O-aryl glycosides, [7d] often reaction efficiencies are disappointingly low.…”

“…[7] Depending on the reaction conditions certain Lewis acids can also produce predominantly -glycosides via acid catalyzed anomerization. [7c,d] While there are reports of high glycosylation yields and good stereocontrol achievable with peracetylated donors, in particular for the synthesis of O-aryl glycosides, [7d] often reaction efficiencies are disappointingly low. [7b] Therefore, despite the fact that classical peracetylated donors can be easily prepared and stored, their use has been largely replaced with more modern glycosyl donors such as trichloroacetimidates and thioglycosides.…”

Superarmed and Superdisarmed Building Blocks in Expeditious Oligosaccharide Synthesis

“…When the arsenal of glycosylation techniques was limited to the Fischer (LG = OH) [11] and Koenigs–Knorr (LG = Cl, Br) [12, 13] approaches (or their variations) [14, 15], oligosaccharide assembly was limited to inefficient stepwise linear techniques. However, as more stable glycosyl donors, such as fluorides [16], thioglycosides [17], and O -alkenyl glycosides were developed [18], the possibility of selective and/or chemoselective activation of one leaving group over another emerged.…”

Expeditious oligosaccharide synthesis via selective, semi-orthogonal, and orthogonal activation

“…52 In 1976, Leroux and Perlin developed the direct dehydrative glycosylation using triflic anhydride in the presence of a sterically hindered base, γ-collidine, and Bu 4 NBr 53,54 The reaction proceeded via a stepwise activation of glycosyl donor 34 via the formation of the anomeric triflate and bromide intermediates. Resultantly, glycosylation of glycosyl acceptor 35 bearing an anomeric acetate group afforded disaccharide 36 in 60% yield (Scheme 11a).…”

“…52 Mukaiyama et al utilized a preactivation-based glycosidation of glycosyl acetate 40 using iodotrimethylsilane followed by the addition of thioglycoside glycosyl acceptor 41 and phosphine oxide (Scheme 12a). 58 Another example involves selective activation of anomeric carbonate 43 over thioglycoside 44 in the presence of TrB(C 6 F 5 ) 4 (Scheme 12b).…”