Polyhydroxylated furans

Furthermore, investigations into reacting even unprotected carbohydrates with 1,3-dicarbonyl compounds have been published in the literature. Controlled by the reaction conditions, the formation of substituted furans or C-glycosides was observed. By application of acidic reaction conditions, multicondensation processes were obtained. As a consequence of that, the formation of polyhydroxylated furans was noticed [38]. These transformations are connected with the loss of stereogenic centers of the carbohydrates deployed. Under basic conditions, a Knoevenagel... 

Polyhydroxylated indolizidine alkaloids, due to their biological activity, have attracted considerable synthetic interest. The total synthesis of ( —)-l-qp/-swainsonine (250) from the chiral imine 238 (Scheme 58) and the parallel synthesis of (+ )-2,8,8a-tri-qp/-swainsonine (252) from the enantiomeric threose A-benzylimine 251, prepared from natural L-tartaric acid, provide further examples of the utility of tartaric acid in meeting the challenge of complex syntheses. A stereospecific 4 + 4 homologation utilizing 2-(trimethylsiloxy)furan (178) pro-... 

When carbonyl compounds with an active methylene group are condensed with sugars (pentoses, hexoses), furans with a polyhydroxylated side chain are obtained possibly y-hydroxy-a, -unsatu-rated ketones are intermediates (Scheme 14) <82BSF(2)176>. 

In a route to polyhydroxylated quinolizidines, condensation between the silyl enol ether 182 and aldehyde 183 (Scheme 34) gave the aldol product 184 with high diatereoselectivity. Conditions were also found to obtain diastereoselective condensations between the enantiomer of 183 and either 182 or its precursor ketone to give stereoisomers of 184. Both 182 and 183 were obtained from furan. 

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