Intervention of catalytic amounts of water in the allylic rearrrangements of glycal derivatives

It is confirmed that tri-O-acetyl-D-gluca1 with thiophenol in the presence of BF3. OEt2 as catalyst gives the allylically rearranged S-phenyl 4,6-di-O -acetyl-2,3-dideoxy-1-thio-alpha- and beta-D-erthyrro-hex-2-enopyranosides as the main products, and now demonstrated that the presence of catalytic p roportions of water diverts the reaction in favour of the isomeric S-phenyl 4,6-di-O-acetyl-2-deoxy-3-phenylthio-1-thio-D-arabino- and -D-ribo-hexopyr anosides, It is proposed that these products are formed from an intermediat e enal. (C) 2000 Elsevier Science Ltd. All rights reserved.