A new approach to the synthesis of oligosaccharides

Unexpected formation of complex bridged tetrazoles via intramolecular 1,3-dipolar cycloaddition of 1,2-O-cyanoalkylidene derivatives of 3-azido-3-deoxy-d-allose

“…Formation of exo-cyanoethylidene 5 is expected to be kinetically favored due to an attack from the sterically less hindered convex side of bicyclic 8. Formation of exo-cyanoethylidenes has been described earlier by others to be favored over the formation of endo-cyanoethylidenes [22][23][24]29 and also corresponds to the preferred formation of exo-isomeric forms of ortho esters. 30 Under the reaction conditions, however, cyanide attack is reversible giving also access to endocyanoethylidene 9.…”

“…[19][20][21] Kochetkov and coworkers utilized cyanoethylidene compounds in Oglycosylation reactions and showed that the C-C bond between the dioxolane carbon and the carbon of the cyano group is relatively weak and can be cleaved with catalytic amounts of Lewis acids such as trityl perchlorate. [22][23][24] Myers et al showed that cyanoethylidene compounds of mannose, glucose, and galactose can be converted to anomeric cyanides under acid promotion without an exogenous cyanide source. 19 Intra-or intermolecular cycloaddition reactions of cyanoethylidene compounds have not been reported before.…”

Glycosylation of a Newly Functionalized Orthoester Derivative

“…The organic extracts were dried (Na 2 SO 4 ), and concentrated in vacuo. (8). To a solution of 7 (54 mg, 0.068 mmol) in pyridine (1 mL) was added Et 3 N (19 µL, 0.14 mmol) at room temperature, and the mixture was stirred overnight.…”

“…In particular, construction of a cyclic carboxonium ion between the C1 and C2 positions is an effective method to obtain the corresponding β-glycosidic linkage of D-sugars, although orthoesters are produced as side products when sterically hindered functional groups are used in glycosyl donors and acceptors [3][4][5][6]. Orthoesters were known to be converted to the corresponding glycosides under acidic conditions, and relatively stable derivatives were employed as glycoside precursors by Kochetkov [7][8][9][10][11] and Kunz [12,13]. We reported the synthesis and reaction of the orthoester 1 (Figure 1), which could be purified by silica gel column chromatography and kept for one month at room temperature [14].…”

General Aspects of the Glycosidic Bond Formation

“…During the 1970s to early 1980s, a few new classes of glycosyl donors were developed. The following compounds are only the most representative examples of the first wave of the leaving-group development: thioglycosides by Ferrier et al [17], Nicolaou et al [18], Garegg et al [19] and others [20]; cyanoethylidene and orthoester derivatives by Kochetkov and coworkers [21,22]; O-imidates by Sinay and coworkers [23] and Schmidt and Michel [24]; thioimidates including S-benzothiazolyl derivatives by Mukaiyama et al [25]; thiopyridyl derivatives by Hanessian et al [26] and Woodward et al [27] and glycosyl fluorides by Mukaiyama et al [28] (Figure 1.2). Many glycosyl donors introduced during that period gave rise to excellent complimentary glycosylation methodologies.…”