N-Protected hydroxyprolines (Hyp) were transformed chemoselectively into alkoxyproline derivatives by direct O-alkylation. The starting Hyp was transformed into the corresponding dianion in a mixture of dimethyl sulfoxide and tetrahydrofuran (1:16 v/v) as solvent. Under these conditions, the carboxy-anion showed reduced nucleophilicity because it was specifically solvated, and the more reactive oxy-anion