N,N′-Transphthaloylation in a Monoprotected Diamine

A convenient and simple method is described for formally transferring a phthaloyl protecting group from one amino group to another in an unsymmetrical diamine. The NMR spectra of some of the amido intermediates reveal that, at room temperature, there is restricted rotation around N-C=O and, in some cases, C-C=O bonds in these molecules.