Pergamon TETRAHEDRON Tetrahedron 54 (1998) 3 159-3 168 Stereoselective Synthesis of Olefinated Sugars’ Albrecht Lieberknecbt*’ , Helmut Griesse~‘, Rodolfo D. Bravo’, Pedro A. Colinas’ and Ra61 J. Grigera’ a: Institut fur Organ&he Chemie und Isotopenforschung der Universititt Stuttgart, Pfaffenwaldring 55, D-70569 stuttgar$ Germany b: Laboratorio de Estudio de Compuestos Orgsmicos, Facultad de Ciencias Exactas Universidad National de La Plata, Calle 47 y 115, 1900 La Plats-Argentina c: Instituto de Fisica de Liquidos y Sistemas Biologicos (IFLYSIB), Facultad de Ciencias Exactas Universidad National de La Plata, CC 505, 1900 La Plats-Argentina Received I December 1997; accepted 19 January 1998 Abuck The stereoselective synthesis of oletinated sugars at the anomeric center via Wittig reaction of a$- giycosyl phosphonium tetrafluoroborates, easily prepared from a& methoxy glycosides, is described. Q 1998 Elsevier Science Ltd. All rights reserved. Until now various types of C-glycosides and qs C-nucleosides showing biological activities have been isolated. Therefore during the last years the chemistry of C-glycosides has attracted much attention and the synthesis of C-glycoside analogues of biologically active molecules became of interest.% During the last years we became interested in the synthesis of C-glycosides, C-glycosylaminoacids3 and especially of sugars which are oleSnated at the anomeric center. This type of C-glycosides shows two specifical features. First Lehmann et al. could demonstrate that these C-glycosides are substrates for P-D-galactosidase’ and a- and B-ghxosidases.’ Next the highly reactive ‘enolether’ function offers numerous possibilities for transformations and can therefore be regarded as a valuable synthon in the synthesis of various new C-glycosides. To date some syntheses especially zc&b for C-methyleneglycosides have been worked out. Recently Chapleur’ reported on the Wittig olefination of sugar lactones with methoxycarbonyl methyltriphenylphosphonium chloride. Numerous glycosylphosphonates were prepared by Vasella et al..’ But as far as we know they have never been used for the construction of C-glycosides. In the formation of Spiro acetals Wittig type reactions using a-alkoxy phosphonium salts have been described.“rO” Herewith we intend to report on the synthesis of C-glycosides olefinated at the anomeric center by the reaction of sugar phosphonium salts with aldehydes (Scheme 1). We apply a method elaborated for the preparation of thioallyl-phosphonium-tetraSuoroborates,’* to synthesize glycosylphosphonium salts starting from a&methoxy sugars which easily can be prepared. For example reaction 00404020/98/$19.00 8 1998 Elsevier Science Ltd. All rights reserved. PII: SOtMO-4020(98)00062-3