the isolated oligomers ranged from 48 % in the first cycle to 29% in the fourth cycle. Having employed a pentenyl-substituted hydroxymethylketoside acceptor in the first cycle, all the derived oligomers contained the pentenyl group at their reducing end. This group was exploited to transform the linear oligomers into cyclic products through intramolecular glycosidation. The major product derived from
phosphonate and a hydroxymethyl (ketosyl derivatives) or carboxymethyl group (ulosonyl derivatives) at the anomeric carbon have been prepared. The synthetic route involves the trimethylsilyltriflate promoted Arbuzov-type coupling between thiazolylketol acetates and triethylphosphite to give thiazolylglycosyl phosphonates in good yields (78–93%). This glycosidation reaction was highly stereoselective giving