Photocatalytic Direct Borylation of Benzothiazole Heterocycles via a Triplet Activation Strategy.

Boron compounds are widely employed in organic chemistry, pharmaceuticals, and materials science. Among them, borylated heterocycles serve as versatile synthons for the construction of new C-C or C-heteroatom bonds via coupling or radical processes. Such methods for direct C-H borylation reactions are of high synthetic value to reduce the number of synthetic steps and the amount of waste and to improve efficiency.

A Photochemical Strategy towards Michael Addition Reactions of Cyclopropenes.

The development of Michael addition reactions to conjugated cyclopropenes is a challenge in organic synthesis due to the fleeting and reactive nature of such strained Michael acceptor systems. Herein, the development of a photochemical approach towards such conjugated cyclopropenes is reported that serves as a strategic entry point to densely functionalized cyclopropanes in a diastereoselective fashion. The process involves the light-mediated generation of transient cyclopropenyl α,β-unsaturated esters from vinyl diazo esters, followed by an organic base catalyzed nucleophilic addition of N-heterocycles to directly access β-N-heterocyclic cyclopropanoic esters.

Oxadiazolone-Based Aromatic Annulations: A Nitrenoid Precursor for Tricyclic Aminoheterocycles.

Nitrogen-containing heterocycles are present in most approved drugs, reflecting the significance of their synthetic strategies. By utilizing oxadiazolone as a nitrenoid (nitrene-like) precursor, we have developed a general strategy for the annulation with nucleophilic heterocycles to access various polycyclic aminoheterocycles. We have discovered that 2-pyrryl-substituted substrates undergo a rearrangement, which indicates a spirocyclization-migration pathway.

Spin States Matter─from Fundamentals toward Synthetic Methodology Development and Drug Discovery.

ConspectusThe potent reactivity of carbenes and nitrenes has been traditionally harnessed by the employment of a transition-metal catalyst in which the reactivity of the metal carbene/nitrene intermediates can be controlled via the judicious tuning of the metal catalyst. In recent years, progress made in this research area has unveiled novel strategies to directly access free carbenes or nitrenes under visible-light-mediated conditions without the necessity of a metal catalyst for stabilization of the carbene/nitrene intermediate. Such photochemical approaches present new opportunities to leverage orthogonal reactions with classic metal-catalyzed transformations.