ZnEt2 as a Precatalyst for the Addition of Alcohols to Carbodiimides

We report here the use of commercially available ZnEt2 as an efficient precatalyst for the addition of alcohols to carbodiimides to obtain a wide range of isoureas under mild conditions. In an initial screening using methanol and commercial carbodiimides as substrates, the bulky isourea (OMe)(NHDipp)-C(NDipp) (Dipp = 2,6-iPr2C6H3) was prepared for the first time using a catalytic method, and its structure confirmed by an X-ray diffraction analysis. Then, the efficiency of the precatalyst was tested with two carbodiimides, C(NiPr)2 and C(Np-tol)2, toward a series of alkylic and arylic alcohols and diols, with different steric and electronic properties, including the presence of other functional groups, usually with excellent conversions, especially for the more reactive aromatic carbodiimide. Some of the new isoureas thus prepared have also been isolated and characterized. Kinetic and stoichiometric experiments allowed us to propose a plausible mechanism for these transformations.

Automated summary

In this study, commercially available ZnEt2 was used as an efficient precatalyst for the addition of alcohols to carbodiimides, resulting in the synthesis of a wide range of isoureas under mild conditions. The bulky isourea (OMe)(NHDipp)-C(NDipp) was prepared for the first time using this catalytic method, and its structure was confirmed. The precatalyst showed high efficiency with various alcohols and diols, including those with different steric and electronic properties, and the obtained isoureas were isolated and characterized.