**Melissa J. Buskes and Maria-Jesus Blanco \***

Medicinal Chemistry. Sage Therapeutics, Inc. 215 First Street, Cambridge, MA 02142, USA; mjbuskes@gmail.com **\*** Correspondence: maria-jesus.blanco@sagerx.com

Academic Editors: José Pérez Sestelo and Luis A. Sarandeses Received: 30 June 2020; Accepted: 29 July 2020; Published: 31 July 2020

**Abstract:** Cross-coupling reactions have played a critical role enabling the rapid expansion of structure–activity relationships (SAR) during the drug discovery phase to identify a clinical candidate and facilitate subsequent drug development processes. The reliability and flexibility of this methodology have attracted great interest in the pharmaceutical industry, becoming one of the most used approaches from Lead Generation to Lead Optimization. In this mini-review, we present an overview of cross-coupling reaction applications to medicinal chemistry efforts, in particular the Suzuki–Miyaura and Buchwald–Hartwig cross-coupling reactions as a remarkable resource for the generation of carbon–carbon and carbon–heteroatom bonds. To further appreciate the impact of this methodology, the authors discuss some recent examples of clinical candidates that utilize key cross-coupling reactions in their large-scale synthetic process. Looking into future opportunities, the authors highlight the versatility of the cross-coupling reactions towards new chemical modalities like DNA-encoded libraries (DELs), new generation of peptides and cyclopeptides, allosteric modulators, and proteolysis targeting chimera (PROTAC) approaches.

**Keywords:** cross-coupling reactions; C-C bond forming reactions; C-Heteroatom bond forming reactions; palladium; clinical candidate; DNA-encoded libraries; cyclopeptides; allosteric modulators; PROTAC
