Variable strategy toward carbasugars and relatives.: 2.: Diversity-based synthesis of β-D-xylo, β-D-ribo, β-L-arabino, and β-L-lyxo 4a-carbafuranoses and (4a-carbafuranosyl)thiols

The silyloxy diene-based construction of carbasugars, previously exploited for the synthesis of four carbocyclic furanose and pyranose analogues, has been investigated further. By introducing a novel silylative cycloaldolization protocol and by adjusting a couple of minor transformations, the efficiency of this synthetic sequence was greatly improved. Through a series of lactone/thiolactone aldehyde cyclization precursors, four carbafuranoses (4a-carba-beta -D-xylofuranose, 4a-carba-beta -D-ribofuranose, 4a-carba-beta -L-arabinofuranose, and 4a-carba-beta -L-lyxofuranose) and four (carbafuranosyl)thiols [(4a-carba-beta -D-xylofuranosyl)thiol, (4a-carba-beta -D-ribofuranosyl)thiol, (4a-carba-beta -L-arabinofuranosyl)thiol, and (4a-carba-beta -L-lyxofuranosyl)thiol] were assembled. From this study, it was shown that these constructions tolerate a variety of precursors, and in many instances, they are suitable for scaling-up.