PREPARATION AND TRANSMETALATION OF A TRIPHENYLSTANNYL BETA-D-GLUCOPYRANOSIDE - A HIGHLY STEREOSELECTIVE ROUTE TO BETA-D-C-GLYCOSIDES VIA GLYCOSYL DIANIONS

The triphenylstannyl beta-D-glucopyranoside 4 was synthesized in one step from the 1,2-anhydro-alpha-D-glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD3OD gave (1S)-1,5-anhydro-3,4,6-tri-O-benzyl-[1-H-2]-D-glucitol (8) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected beta-D-configurated products 11, 12, and 13 in good yields. Preparation of C-acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14. Treatment of 7 with MeI led to 15 (30%) along with 40% of 18, C-alkylation being accompanied by halogen-metal exchange. Prior addition of lithium 2-thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15. No alpha-D-anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17.