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
Abstract
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.