A Palladium-Catalyzed Multicomponent Synthesis of Imidazolinium Salts and Imidazolines from Imines, Acid Chlorides, and Carbon Monoxide

A palladium-catalyzed multicomponent synthesis of imidazolinium carboxylates and imidazolines is described. The palladium catalyst [Pd(CH(R-1)N(R-2)COR3)Cl](2), or [Pd(allyl)Cl](2), with P(t-Bu)(2)(2-biphenyl) can mediate the simultaneous coupling of two imines, acid chloride, and carbon monoxide into substituted imidazolinium carboxylates within hours under mild conditions (45 degrees C, 4 atm of CO). The reaction proceeds in good yield with aryl-, heteroaryl-, and alkyl-substituted acid chlorides, as well as variously functionalized imines. Imidazolines are formed via the initial generation of Munchnone intermediates, followed by their cycloaddition with an in situ generated protonated imine. The addition of an amine base can intercept catalysis at Munchnone formation, which allows the subsequent cycloaddition of a second imine. The latter provides a route for the assembly of complex, polysubstituted imidazolinium carboxylates with independent control of all five substituents. The subsequent removal of the nitrogen substituent(s) provides an overall synthesis of imidazolines.