| Abstract: | Many different approaches for synthesis of branched chain sugars have beenestablished,1 because they are very useful intermediates for synthesis of other non-sugar chiralmolecules, and usually occur in nature. Branched chain glycosidulose can be used for construction offive- and six-membered carbocyclic rings to which two chiral carbons of sugar are incorporated byintramolecular aldol condensation and Robinson annulation,2 Therefore they are useful in thesynthesis of natural products which consist of annulated carbohydrates or where a highlyfunctionalised enantiomerically pure cyclopentane or cyclohexane is required. Also, this type ofbranched chain sugar can be considered as the synthons of monoterpenoid natural products of theiridoid class which have the cyclopentan-(c)-pyran structure. In view of the importance of branchedchain glycosiduloses, it is desirable to have a general, convenient methodology to their synthesis.However, none of the literature methods was reported on their synthesis by a nuclephilic addition toa partially protected glycosidulose, due to the fact that these glycosiduloses are very difficult tosynthesize selectively and unstable;3 and what is more, one-step synthesis branched chainglycosidulose using this method is almost impossible.In this paper, we report on a general, convenient method for stereoselective syntheses of2,2-bis(C-branched-chain)glucopyranosid-3-uloses by the new reaction of 1 with various activemethylene compounds. The generality of this method was examined in detail. The optimumtemperature was 18-25℃. The solvent DMF was better than the others. In all cases he yields werehigher than 60%.All the 2,2-bis(C-branched-chain)glucopyranosid-3-uloses were characterized by X-raycrystallographic analyses. In addition, the important iintermediate in this reaction was isolated,which is the product of autoxidation of 1 at C-3 position. Thus the reaction mechanism for thesynthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-uloses can be rationalized by autoxidationof 1 followed by 1,4-Michael addition of various carbanions as the main steps. |
