Chemoselective N-alkylation of di-N,O-protected tyrosine through specific oxy-anion solvation by non-hydrogen bonding donor solvents

N-(2-Nitro-benzenesulfonyl) activated L-tyrosine methyl ester has been directly N-alkylated under solid-liquid phase-transfer catalysis (SL-PTC) conditions and in a coordinating non-hydrogen bonding donor (non-HBD) solvent, which reduces through specific solvation the nucleophilicity of the oxy-anionic center of the N,O-dianion formed by action of an anhydrous inorganic carbonate.