S-O acetyl rearrangement in 6-thio-D-glucose derivatives

Abstract

The solvolytic reaction of 1,2-O-isopropylidene-3,6-di-O-(p-toluenesulphonyl)- ?-D-glucofuranose (2), as well as that of 6-chloro-6-deoxy-1,2-O-isopropylidene-3-O-(p-toluenesulphonyl)-?-D-glucofuranose (3), in the presence of potassium thioacetate unexpectedly gave the 6-S-acetyl-5-O-acetyl derivative 5 as the main reaction product. A possible mechanism of these transformations was postulated whereby the main role was ascribed to a neighbouring group participation process, involving hydrogen thio-orthoester formation as an intermediate. The regiospecific monosubstitution of the 6-tosyloxy group in compound 2 was successfully achieved with potassium thioacetate, in presence of 2,3-benzo-15-crown-5 as a catalyst. The corresponding 6-S-acetyl derivative 7 was obtained representing a possible intermediate in the mentioned solvolytic reactions. Compound 7 was shown to be very reactive, since it fully transformed into the corresponding mercaptan 8 in the presence of silica gel. This transformation occurred via the same thio-orthoester 7a as in the mentioned solvolytic reactions of furanoses 2 and 3. The synthesized compounds are key intermediates in the planned synthesis of selected natural products and their analogues.