Environmentally Benign Synthesis of Sugar Orthoesters Promoted by Anhydrous Sodium Acetate and Ultrasound

Abstract

A convenient and alternative procedure for the synthesis of sugar orthoesters from glycosyl bromides with anhydrous sodium acetate as base under ultrasound irradiation is described. Various sugar and sugar-sugar orthoesters were prepared in 70%-91% isolated yields.

Applications of alkyl orthoesters as valuable substrates in organic transformations, focusing on reaction media

“…The results conrmed that an ultrasound-assisted reaction proceeded much better than the traditional method (70-91% yields, 3-6 h) (Scheme 10). 91 The reaction of dilactone (46) with ethylene glycol (47) by ptoluenesulfonic acid (p-TSA) in the presence of magnesium sulfate in reuxing benzene obtained the crystalline ethylene orthoester (48) in 66% yield within 4.5 h, which underwent a reduction reaction with diisobutylaluminum hydride as a reducing agent in combined dimethoxyethane/toluene (1 : 2) media at À76 C to room temperature to afford the hydroxy aldehyde (49) in 94% yield (Scheme 11). 92 Hexachlorobuta-1,3-diene (50) was reuxed with sodium methoxide in methanol for 12 h to obtain a mixture of 4,4dimethoxy-2-oxobut-3-enoic acid (51) and (Z)-2,4,4-trichloro-1,1,1,3-tetramethoxybut-2-ene (52) in 39% and 54% yields, respectively in which for easy identication, compound (51) was reacted with diazomethane (CH 2 N 2 ) in methanol at room temperature to produce methyl (Z)-4,4-dimethoxy-2-oxobut-3enoate (53) in moderate yield (56%), while orthoester Z-52 was converted into methyl (Z)-2,4,4-trichloro-3-methoxybut-2-enoate (Z-54) in good yield (70%) via acid hydrolysis in THF at 50 C for 2 h (Scheme 12).…”

“…The results confirmed that an ultrasound-assisted reaction proceeded much better than the traditional method (70–91% yields, 3–6 h) ( Scheme 10 ). 91 …”