Displacement reactions on 2,3,4,6-tetra-O-benzyl-1,5-di-O-sulfonyl-D-glucitols. Synthesis of (3R,4S)-3,4-dibenzyloxy-2-(2-benzyloxyethylidene)tetrahydrofuran
摘要:
Treatment of the 1,5-dimesylate and 1,5-ditosylate of 2,3,4,6-tetra-O-benzyl-D-glucitol 1 with tetrabutylammonium acetate in acetonitrile leads, through nucleophilic attack by O-2 at C-5 and normal displacement at C-1, to 1-O-acetyl-2,5-anhydro-3,4,6-tri-O-benzyl-L-iditol. In contrast, the corresponding 1,5-ditriflate on similar treatment undergoes displacement at C-1 by attack of O-4 and elimination of triflic acid between C-4 and C-5 to afford (3R,4S)-3,4-dibenzyloxy-2-(2-benzyloxyethylidene)tetrahydrofuran.
We describe herein a convenient strategy for the construction of C,C-glycoside building blocks via the intermediacy of tertiary pseudoanomeric radicals. Application of an iron-mediated hydrogen atom transfer/Michael–Giese coupling enables the anomeric quaternization of readily available exo-glycals with good to complete stereocontrol in the pyranose and furanose series. Carefully optimized conditions
A general synthetic route was developed for the preparation of the first example of a new series of modified C‐nucleoside phosphonate analogues bearing a l‐threose sugar moiety and pyrrolo[2,1‐f][1,2,4]triazin‐4‐amine as nucleobase.
A stereodivergent synthesis of the first examples of 4-membered carbasugars has been achieved from vitamin C by way of an efficient intramolecular SmI2-mediated aldehyde-alkene coupling. In this key step, cylobutanes with four contiguous asymmetric centers are generated with a high level of stereocontrol.