Catalytic Diastereo- and Enantioselective Synthesis of 2-Imidazolinones.

Chiral cyclic ureas (2-imidazolinones) were prepared by the reaction of nitrones and isocyanoacetate esters using a multicatalytic system that combines a bifunctional Brønsted base-squaramide organocatalyst and Ag+ as a Lewis acid. The reaction could be achieved with a range of nitrones derived from aryl- and cycloalkylaldehydes with moderate diastereo- and good enantioselectivity. A plausible mechanism involving an initial formal [3 + 3] cycloaddition of the nitrone and isocyanoacetate ester, followed by rearrangement to an aminoisocyanate and cyclization to the imidazolinone, is proposed.