Galactosyl phosphites

Wong and co-workers reported that the galactosylation of trihydroxy sugar 109 with a-galactosyl phosphite donor 108 having an 0-6 acetyl group produced disaccharide 110 (p/a = 15 85) with an excess of the a-anomer, which could be formed by the remote participation of the acetyl group at 0-6 (Scheme 18) [70]. 

Cheng, Y-P, Chen, H-T, Lin, C-C, A convenient and highly stereoselective approach for a-galactosylation performed by galactopyranosyl dibenzyl phosphite with remote participating groups. Tetrahedron Lett, 43, 7721-7723, 2002. 

Full details have appeared on the use of 0-protected glycosyl phosphites for Lewis acid-catalysed glycosidation (cf. Synlett, 1993, 115). Again anomeric mixtures were produced, but reasonable yields resulted - especially when O-benzyl protection was employed with glucosyl, galactosyl and mannosyl donors and with 0-acetylated sialic acid donor. 

The galactosyl amine derivative 122 undergoes stereoselective addition (up to 86% d.e.) of diethyl phosphite to provide, after acidic cleavage of the auxiliary, (S)-o-amino phosphonic acids (Scheme 26). 2... 

Glycosylation using Galactosyl and Fucosyl Phosphites with a Benzyl Group at C-2... 

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