DBU (1, 8-diazabicyclo [5.4. 0] undecene) was found to cfliciently mediate the transesterification of p-nitrophenyl (PNP) phosphon-ates by various alcohols. The reactions of bis-PNP phosphonates in the presence of DBU, using both primary and secondary alcohols, phenols and amines, proceed rapidly and with high yield to afford the corresponding monoalkyl/aryl mono-PNP phosphonates as sole products (1, Scheme 2). ...