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

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 CD 3 OD gave (1 S )‐1,5‐anhydro‐3,4,6‐tri‐ O ‐benzyl‐[1‐ 2 H]‐ 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 .