Mechanism and application of a microcapsule enabled multicatalyst reaction

In this paper, we describe the development and application of a multistep one-pot reaction that is made possible by the site isolation of two otherwise incompatible catalysts. We prepared a microencapsulated amine catalyst by interfacial polymerization and used it in conjunction with a nickel-based catalyst for the transformation of an aldehyde to a Michael adduct via a nitroalkene intermediate. The amine-catalyzed conversion of an aldehyde to a nitroalkene was found to proceed through an imine rather than a nitroalcohol. Kinetic studies indicated that the reaction is first order in both the nickel catalyst and the shell of the encapsulated amine catalyst. Furthermore, we provide evidence against interaction between amine and nickel catalysts and present kinetic data that demonstrates that there is a rate enhancement of the Michael addition due to the urea groups on the surface of the microencapsulated catalyst. We applied our one-pot reaction to the development of a new synthetic route for pregabalin that proceeds with an overall yield of 74%.