Synthesis of Carbon‐Bridged C‐Lactose and Derivatives

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Abstract
4‐C‐Formylglucopyranoside 9 was readily obtained from 4‐O‐unprotected glucose derivative 4 in four steps, each step giving a high product yield. Reaction with 1‐C‐lithiated 2‐phenylsulfinyl‐D‐galactal 10 as nucleophile furnished C‐disaccharide intermediates 11a and 11b as diastereoisomers. Ensuing removal of the phenylsulfinyl group with Raney nickel and regio‐ and diastereospecific 2b‐hydrogen and 3b‐hydroxy transfer afforded β(1–4)‐connected C‐lactosides 13a and 13b, respectively; their structures were deduced from derivatives 14a, b and 16a, b on the basis of 1H‐NMR data. Hydrogenolytic O‐debenzylation of 13a and 13b afforded hydroxymethylene‐bridged C‐lactose 2a and 2b, respectively. Regioselective O‐benzylation of 13a gave preferentially 1b‐O‐unprotected derivative 17aa which furnished upon oxidation carbonyl‐bridged C‐lactose derivative 19. Deoxygenation at C‐1b of 17aa and subsequent hydrogenolytic O‐debenzylation furnished methylene‐bridged C‐lactose 1.