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6-Chloropurine and 2,6-dichloropurine were regioselectively glycosylated at position 7 to give the corresponding peracetylated N 7 -nucleosides, which can be suitable for other purine transformations. In this work, we study the distribution of N 7 / N 9 -isomers produced via the Vorbrüggen method under different conditions, using an N -trimethylsilylated purine derivative and SnCl 4 or TiCl 4 as a catalyst. The main effort is devoted to reversing the disadvantageous predominant selectivity of most glycosylation reactions at the N 9 position and thus to determining conditions that maximize the regioselectivity of glycosylation toward the desired N 7 -isomer.