Cascade cyclization of alkene-tethered acylsilanes and allylic sulfones enabled by unproductive energy transfer photocatalysis

Photoinduced Asymmetric Formal Siloxycarbene Insertion into sp3 C-H Bonds Enabled by Chiral Phosphoric Acid

We disclosed herein an enantioselective formal siloxycarbene insertion reaction enabled by chiral phosphoric acid and blue LED irradiation. This is the first time the asymmetric siloxycarbene insertion into an sp3 C-H bond under transition-metal free conditions has been realized. The reaction features good isolated yields (up to 92%), high enantioselectivity (up to 99:1 er), mild reaction conditions, and good compatibility. Moreover, this method also provides a green and efficient method to construct a chiral quaternary carbon center.

Photocatalytic Synthesis of Indanone, Pyrone, and Pyridinone Derivatives with Diazo Compounds as Radical Precursors

We disclose herein a photocatalytic radical cascade cyclization of diazoalkanes for the divergent synthesis of important carbocycles and heterocycles. Under the optimal reaction conditions, various indanone, pyrone, and pyridinone derivatives can be obtained in moderate to good yields. Mechanistic experiments support the formation of carbon-centered radicals from diazoalkanes through the proton-coupled electron transfer process. Scale-up reaction using continuous flow technology and useful downstream application of the formed heterocycles further render the strategy attractive and valuable.

Chemoselective Synthesis of Unsymmetrical Dithioacetals through Sequential Carbene Insertion and Acetal Exchange of Acylsilanes and Thiols under Visible Light Irradiation

Dithioacetals are a frequently used motif in synthetic organic chemistry, and most existing reports discuss only symmetrical dithioacetals. Examples of unsymmetrical dithioacetals are scarce, and few general methods for the selective synthesis of these compounds exists. An intriguing visible-light-induced strategy has been established in this work for sequential reactions of S-H insertion and acetal exchange between acylsilanes and two different thiols that deliver a wide variety of unsymmetrical dithioacetals in moderate yields. The unsymmetrical dithioacetals were obtained with high selectivity, and a great variety of functional groups were tolerated.

Rejuvenation of dearomative cycloaddition reactions via visible light energy transfer catalysis

Dearomative cycloaddition is a powerful technique to access sp3-rich three-dimensional structural motifs from simple flat, aromatic feedstock. The building-up of unprecedentedly diverse polycyclic scaffolds with increased saturation and stereochemical information having various applications ranging from pharmaceutical to material sciences, is an essential goal in organic chemistry. However, the requirement of large energy inputs to disrupt the aromaticity of an arene moiety necessitates harsh reaction conditions for ground state dearomative cycloaddition. The photochemical requirement encompasses use of ultraviolet (UV) light to enable the reaction on an excited potential energy surface. The microscopic reversibility under thermal conditions and the use of high energy harmful UV irradiation in photochemical manoeuvres, however, constrain their widespread use from a synthetic point of view. In this context, the recent renaissance of visible light energy transfer (EnT) catalysis has become a powerful tool to initiate dearomative cycloaddition as a greener and more sustainable approach. The excited triplet state population is achieved by triplet energy transfer from the appropriate photosensitizer to the substrate. While employing mild visible light energy as fuel, the process leverages an enormous potential of excited state reactivity. The discovery of an impressive portfolio of organic and inorganic photosensitizers with a range of triplet energies facilitates visible light photosensitized dearomative cycloaddition of various substrates to form sp3-rich fused polycyclic architectures with diverse applications. The tutorial review comprehensively surveys the reawakening of dearomative cycloadditions via visible light-mediated energy transfer catalysis in the past five years. The progress ranges from intra- and intermolecular [2π + 2π] to [4π + 2π], and ends at intermolecular [2π + 2σ] cycloadditions. Furthermore, the review provides potential possibilities for future growth in the growing field of visible light energy transfer catalysis.

Copper-Catalyzed 1,4-Trifluoromethylthio-Arylsulfonylation of 1,3-Enynes via the Insertion of Sulfur Dioxide

A copper-catalyzed trifluoromethylthio-arylsulfonylation between 1,3-enynes, AgSCF3, aryldiazonium tetrafluoroborates, and SO2 (from SOgen) is presented, which could introduce sulfone, SCF3, and allene moieties into one molecule simultaneously. This strategy features mild reaction conditions, good substrate compatibility, and excellent regioselectivity. The products obtained have the potential for further conversion into other valuable compounds. Initial investigations into the reaction mechanism suggest that it may proceed via a radical pathway. Notably, SOgen was proven as a uniquely effective SO2 surrogate in this transformation.