Preparation and Transmetallation of a Triphenylstannyl β‐D‐Glucopyranoside: A highly stereoselective route to β‐D‐C‐glycosides via glycosyl dianions

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Abstract
The triphenylstannyl β‐D‐glucopyranoside 4 was synthesized in one step from the 1,2‐anhydro‐α‐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‐[1‐2H]‐D‐ glucitol (8) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β‐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 α‐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.