Translating Planar Heterocycles into Three-Dimensional Analogs by Photoinduced Hydrocarboxylation

The rapid preparation of complex three-dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three-dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high-throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules.

Photosynthetic Fixation of CO2 in Alkenes by Heterogeneous Photoredox Catalysis with Visible Light

Light-driven fixation of CO2 in organics has emerged as an appealing alternative for the synthesis of value-added fine chemicals. Challenges remain in the transformation of CO2 as well as product selectivity due to its thermodynamic stability and kinetic inertness. Here we develop a boron carbonitride (BCN) with the abundant terminal B/N defects around the mesoporous walls, which essentially enhances surface active sites as well as charge transfer kinetics, boosting the overall rate of CO2 adsorption and activation. In this protocol, anti-Markovnikov hydrocarboxylation of alkenes with CO2 to an extended carbon chain is achieved with good functional group tolerance and specific regioselectivity under visible light irradiation. The mechanistic studies demonstrate the formation of CO2 radical anion intermediate on defective boron carbonitride, leading to the anti-Markovnikov carboxylation. Gram-scale reaction, late-stage carboxylation of natural products and synthesis of anti-diabetic GPR40 agonists reveal the utility of this method. This study sheds new insight on the design and application of metal-free semiconductors for the conversion of CO2 in an atom-economic and sustainable manner.