Variable strategy toward carbasugars and relatives. 2. Diversity-based synthesis of beta-D-xylo, beta-D-ribo, beta-L-arabino, and beta-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 cycloaldolizat ion protocol and by adjusting a couple of minor transformations, the effici ency of this synthetic sequence was greatly improved. Through a series of l actone/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 (carbafurano syl)thiols [(4a-carba-beta -D-xylofuranosyl)thiol, (4a-carba-beta -D-ribofu ranosyl)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 instance s, they are suitable for scaling-up.