Light-Driven Single-Electron Transfer Processes as an Enabling Principle in Sulfur and Selenium Multicatalysis.

Cooperativity has become a mainstay in the context of multicatalytic reaction design. The combination of two or more catalysts that possess mechanistically distinct activation principles within a single chemical setting can enable bond constructions that would be impossible for any of the catalysts alone. An emerging subdomain within the field of multicatalysis is characterized by single-electron transfer processes that are sustained by the synergistic merger of sulfur or selenium organocatalysis with photoredox catalysis. From a synthetic viewpoint, such processes have tremendous value, as they can offer new and economic pathways for the concise assembly of complex molecular architectures. Thus, the aim of this Review is to highlight recent methodological progress made in this area and to contextualize representative transformations with the mechanistic underpinnings that enable these reactions.

Photocatalytic Aerobic Phosphatation of Alkenes.

A catalytic regime for the direct phosphatation of simple, non-polarized alkenes has been devised that is based on using ordinary, non-activated phosphoric acid diesters as the phosphate source and O2 as the terminal oxidant. The title method enables the direct and highly economic construction of a diverse range of allylic phosphate esters. From a conceptual viewpoint, the aerobic phosphatation is entirely complementary to traditional methods for phosphate ester formation, which predominantly rely on the use of prefunctionalized or preactivated reactants, such as alcohols and phosphoryl halides. The title transformation is enabled by the interplay of a photoredox and a selenium π-acid catalyst and involves a sequence of single-electron-transfer processes.

Synthesis of (+)-Greek Tobacco Lactone via a Diastereoablative Epoxidation and a Selenium-Catalyzed Oxidative Cyclization.

An asymmetric synthesis of the C11-homoterpenoid (+)-Greek tobacco lactone is developed starting from readily available (R)-linalool. The synthesis is comprised of four operations and features a diastereoablative epoxidation and an oxidative tetrahydropyran formation using vanadium-, palladium-, and selenium-catalyzed cyclizations.

Oxidative Allylic Esterification of Alkenes by Cooperative Selenium-Catalysis Using Air as the Sole Oxidant.

A new metal-free catalysis protocol for the oxidative coupling of nonactivated alkenes with simple carboxylic acids has been established. This method is predicated on the cooperative interaction of a diselane and a photoredox catalyst, which allows for the use of ambient air or pure O2 as the terminal oxidant. Under the title conditions, a range of both functionalized and nonfunctionalized alkenes can be readily converted into the corresponding allylic ester products with good yields (up to 89%) and excellent regioselectivity as well as good functional group tolerance.