The reactivity of furanoid and pyranoid glycals towards aromatic Grignard reagents and a nickel catalyst

By reaction with aromatic Grignard reagents in the presence of low valent n ickel species at low temperature, the 1,2-unsaturated furanoid glycal (1) u ndergoes coupling reaction to produce 2,3-unsaturated products (1a,b) as pu re stereoisomers. When these reaction conditions are applied to protected 1 ,2-unsaturated pyranoid glycals (2, 3, 4), both cross-coupling and eliminat ion reactions occur to give conjugated diene-alcohol derivatives (2a; 3a,b; 4a,b, respectively), in moderate yield. (C) 1999 Elsevier Science Ltd. All rights reserved.