Synthesis of 2,3,4,6-tetra-O-benzyl-D-glucal on the gram scale.A convenient method for its facile synthesis and subsequent stereoselective cyclopropanation

摘要

Due to their utility in a variety of processes,glycals have received considerable attention in the carbohydrate field.Examples include Danishefsky's epoxidation/gly-cosidation methodology,Ferrier-type rearrangements,cyclopropanations,C-glycosylations,and metal-catalyzed transformations.Reports on the use of 2,3,4,6-tetra-O-benzyl-D-glucal (1),however,have been limited,perhaps due to its low yielding and problematical synthesis.The most recently reported synthesis involves the mesylation then Pd(PPh_3)_4-catalyzed elimination of 2 (Eq.I).We have found this strategy to be difficult as the use of pristine methanesulfonic anhydride is required,purification of 1 by radial chromatography is required,and the synthesis of 2 is low yielding (29%).Other reports of the formation of 1 as byproducts in reactions of diazirines have also appeared,but these do not appear to be synthetically useful.