Ferrier glycal allylic rearrangement

Abstract

In the presence of Lewis acid catalysts O-substituted glycal derivatives can react with O-, S-, C- and, less frequently, N-, P- and halide nucleophiles to give 2,3unsaturated glycosyl products.1,2This allylic transformation has been termed the “Ferrier Reaction” or, to avoid complications, the “Ferrier I Reaction” or the “Ferrier Rearrangement”. However, the reaction was first noted by Emil Fischer when he heated tri-O-acetyl-D-glucal in water.3When carbon nucleophiles are involved, the term “Carbon Ferrier Reaction” has been used,4 although the only contribution the Ferrier group made in this area was to find that tri-O-acetyl-D-glucal dimerizes under acid catalysis to give a C-glycosidic product.5 The general reaction is illustrated by the separate conversions of tri-O-acetyl-D-glucal with O-, S- and C-nucleophiles to the corresponding 2,3-unsaturated glycosyl derivatives. Normally, Lewis acids are used as catalysts, boron trifluoride etherate being the most common. Allyloxycarbenium ions are involved as intermediates, high yields of products are obtained, and glycosidic compounds with quasi-axial bonds (as illustrated) predominate (commonly in the α,β-ratio of about 7:1). The examples illustrated4,6,7 are typical of a very large number of literature reports.1