Rate versus selectivity determining: The measurement of a kinetic isotope effect (KIE) can provide valuable information about the mechanism of a reaction, but care must be taken in the design and interpretation of KIE experiments. Depending on the experiment that is conducted, the observation of a primary KIE resulting from H/D substitution does not necessarily imply that CH bond cleavage occurs during the rate‐determining step of a reaction. FG=functional group.

New synthetic methods for the catalytic functionalization of C-H bonds have the potential to revolutionize the synthesis of complex molecules. However, the realization of this synthetic potential requires the ability to functionalize selectively one C-H bond in a compound containing many such bonds and an array of functional groups. The site-selective functionalization of aliphatic C-H bonds is one of the greatest challenges that must be met for C-H bond functionalization to be used widely in complex-molecule synthesis, and processes catalysed by transition-metals provide the opportunity to control selectivity. Current methods for catalytic, aliphatic C-H bond functionalization typically rely on the presence of one inherently reactive C-H bond, or on installation and subsequent removal of directing groups that are not components of the desired molecule. To overcome these limitations, we sought catalysts and reagents that would facilitate aliphatic C-H bond functionalization at a single site, with chemoselectivity derived from the properties of the catalyst and site-selectivity directed by common functional groups contained in both the reactant and the desired product. Here we show that the combination of an iridium-phenanthroline catalyst and a dihydridosilane reagent leads to the site-selective γ-functionalization of primary C-H bonds controlled by a hydroxyl group, the most common functional group in natural products. The scope of the reaction encompasses alcohols and ketones bearing many substitution patterns and auxiliary functional groups; this broad scope suggests that this methodology will be suitable for the site-selective and diastereoselective functionalization of complex natural products.

As companies grow ever more mindful of the sustainability aspects of their products and supply chains, an increasing focus on the environmental impact of pharmaceutical manufacture spurs innovation from chemists who support this industry. Metal catalysis has the potential to greatly enhance the sustainability of pharmaceutical products, leading to shorter and more efficient synthetic routes and more direct access to single stereoisomeric products. This perspective article seeks to highlight a number of important considerations for the design of new and improved sustainable metal-catalyzed transformations in order to facilitate rapid adoption by the pharmaceutical industry.

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