An unprecedented access to trifluoromethylthiosugar derivatives from thiocyanate precursors upon treatment with trifluoromethyltrimethylsilane

Upon treatment with trifluoromethyltrimethylsilane (2 equiv) in oxolane at 0 degrees C in the presence of a catalytic amount of tetra-n-butylammonium fluoride (0.2 equiv), various protected sugar derivatives having a thiocyanato group attached to different positions (anomeric, secondary, primary) were converted into the corresponding trifluoromethylthio derivatives. Under these conditions, highly selective, albeit partial transformations of primary and secondary thiocyanate groups were achieved while a decreased selectivity was observed when the reaction involved a more reactive anomeric thiocyanate group. However, in this case, lowering the reaction temperature led to enhanced selectivity and higher isolated yields. The isopropylidene and benzoyl protecting groups in the resulting trifluoromethylthiosugar derivatives were removed by standard methods to afford the corresponding free trifluoromethylthio derivatives, generally in high yield and as crystalline solids. Hence, this method opens a practical access to new trifluoromethylthiosugars obtained under smooth conditions as protected or unprotected derivatives. (C) 1998 Elsevier Science Ltd. All rights reserved.