A synthesis of abemaciclib utilizing a Leuckart-Wallach reaction

A concise total synthesis of CDK 4/6 inhibitor abemaciclib is described. The synthesis uses a Suzuki coupling, followed by a Hartwig-Buchwald amination to join three of the four subunits. The final step is a reductive amination utilizing Leuckart-Wallach conditions. Key to the Leuckart-Wallach reaction was the addition of trimethyl orthoformate to remove water formed during the reaction, allowing the reaction to go to completion. (C) 2014 Elsevier Ltd. All rights reserved.