Direct C-H Radiocyanation of Arenes via Organic Photoredox Catalysis.

Innovative labeling methods to incorporate the short-lived positron emitter carbon-11(11C) into bioactive molecules are attractive for positron emission tomography (PET) tracer discovery. Herein, we report a direct C-H radiocyanation method that incorporates [11C]cyanide (11CN-) to a series of functional electron-rich arenes via photoredox catalysis. This photoredox-mediated radiocyanation can proceed in an aerobic environment and is not moisture sensitive, which allows for ease of reaction setup and for scalable synthesis of 11C-aryl nitriles from readily available precursors.

Homobenzylic Oxygenation Enabled by Dual Organic Photoredox and Cobalt Catalysis.

Activation of aliphatic C(sp3)-H bonds in the presence of more activated benzylic C(sp3)-H bonds is often a nontrivial, if not impossible task. Herein we show that leveraging the reactivity of benzylic C(sp3)-H bonds to achieve reactivity at the homobenzylic position can be accomplished using dual organic photoredox/cobalt catalysis. Through a two-part catalytic system, alkyl arenes undergo dehydrogenation followed by an anti-Markovnikov Wacker-type oxidation to grant benzyl ketone products. This formal homobenzylic oxidation is accomplished with high atom economy without the use of directing groups, achieving valuable reactivity that traditionally would require multiple chemical transformations.

Site-Selective C-H Alkylation of Piperazine Substrates via Organic Photoredox Catalysis.

Piperazine-containing compounds serve as one of the most important classes of compounds throughout all fields of chemistry. Alas, current synthetic methods have fallen short of providing a general method for the synthesis of highly decorated piperazine fragments. Herein, we present a site-selective approach to the C-H functionalization of existing piperazine compounds using photoredox catalysis. This manifold relies on the predictable differentiation of electronically distinct nitrogen centers within the piperazine framework, granting access to novel C-alkylated variants of the starting piperazines.

Generation and Alkylation of α-Carbamyl Radicals via Organic Photoredox Catalysis.

Strategies for the direct C-H functionalization of amines are valuable as these compounds comprise a number of pharmaceuticals, agrochemicals and natural products. This work describes a novel method for the C-H functionalization of carbamate-protected secondary amines via α-carbamyl radicals generated using photoredox catalysis. The use of the highly oxidizing, organic acridinium photoredox catalyst allows for direct oxidation of carbamate-protected amines with high redox potentials to give the corresponding carbamyl cation radical. Following deprotonation, the resultant open-shell species can be intercepted by a variety of Michael acceptors to give elaborate α-functionalized secondary amines. The reaction proceeds under mild conditions without the requirement of exogenous redox mediators or substrate prefunctionalization. Additionally, we were able to showcase the utility of this methodology through the enantioselective synthesis of the indolizidine alkaloid, (+)-monomorine I.

Predictive Model for Site-Selective Aryl and Heteroaryl C-H Functionalization via Organic Photoredox Catalysis.

Direct C-H functionalization of aromatic compounds is a useful synthetic strategy that has garnered much attention because of its application to pharmaceuticals, agrochemicals, and late-stage functionalization reactions on complex molecules. On the basis of previous methods disclosed by our lab, we sought to develop a predictive model for site selectivity and extend this aryl functionalization chemistry to a selected set of heteroaromatic systems commonly used in the pharmaceutical industry. Using electron density calculations, we were able to predict the site selectivity of direct C-H functionalization in a number of heterocycles and identify general trends observed across heterocycle classes.

Direct C-H Cyanation of Arenes via Organic Photoredox Catalysis.

Methods for the direct C-H functionalization of aromatic compounds are in demand for a variety of applications, including the synthesis of agrochemicals, pharmaceuticals, and materials. Herein, we disclose the construction of aromatic nitriles via direct C-H functionalization using an acridinium photoredox catalyst and trimethylsilyl cyanide under an aerobic atmosphere. The reaction proceeds at room temperature under mild conditions and has proven to be compatible with a variety of electron-donating and -withdrawing groups, halogens, and nitrogen- and oxygen-containing heterocycles, as well as aromatic-containing pharmaceutical agents.