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 thiocyan ato group attached to different positions (anomeric, secondary, primary) we re converted into the corresponding trifluoromethylthio derivatives. Under these conditions, highly selective, albeit partial transformations of prima ry and secondary thiocyanate groups were achieved while a decreased selecti vity was observed when the reaction involved a more reactive anomeric thioc yanate 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 derivat ives were removed by standard methods to afford the corresponding free trif luoromethylthio derivatives, generally in high yield and as crystalline sol ids. Hence, this method opens a practical access to new trifluoromethylthio sugars obtained under smooth conditions as protected or unprotected derivat ives. (C) 1998 Elsevier Science Ltd. All rights reserved.