Conversion of glucosamine to galactosamine and allosamine derivatives: Control of inversions of stereochemistry at C-3 and C-4

The reactions of sodium benzoate with a series of trimesylates derived from glucosamine have been examined in an attempt to gain facile access to gala ctosamine analogues. Trimesylate 17, in which the amino group was protected as a phthalimide, underwent double displacement at positions 4 and 6 to gi ve the dibenzoate 18 with the desired galactosamine configuration. In contr ast, trimesylates 21 and 27, in which the amino groups were protected as ac etamides, unexpectedly underwent double displacement at positions 3 and 6, giving products 22 and 28, respectively, with allosamine configurations.