. . "(b) condensing the imine thus prepared with an anion produced by abstraction of the bromine or iodine atom from a compound of formula (XIX): wherein R5 is a bromine or iodine atom, R6 is an N-protecting group, B??? and D??? are independently selected from H, OR7 and N(R8)2, and R7 and R8 are O- and N-protecting groups respectively to produce a 1-C-(pyrrolo[3,2-d]pyrimidin-7-yl)-1,4-dideoxy-1,4-imi" . .