Figure 1: Various methods used for the formation of 1,2-cis-glycosides.
From: Automated assembly of oligosaccharides containing multiple cis-glycosidic linkages
(a) A non-participating protecting group at C2 results in a mixture of anomers. (b) Intramolecular aglycon delivery with a C2 2-naphthylmethyl (NAP)-ether produces predominantly the β-anomer. (c) Hydrogen-bond-mediated aglycan delivery using picolinyl and picoloyl protecting groups at the C6 position of glucose provide high selectivity. (d) Chiral auxiliaries ensure complete selectivity. (e) Additive (or solvent)-modulation results in predominant to exclusive formation of 1,2-cis-glycosides. (f) Remote participating groups result in good selectivities. Ac, acetate; Bn, benzyl; DMF, dimethylformamide; LG, leaving group; Nap, naphthyl; [O], oxidation; PG, protecting group; Pico, picoloyl; ROH, acceptor; Ph, phenyl.
