Photoinduced Site-Selective Aryl C-H Borylation with Electron-Donor-Acceptor Complex Derived from B2Pin2 and Isoquinoline.

Due to boron's metalloid properties, aromatic boron reagents are prevalent synthetic intermediates. The direct borylation of aryl C-H bonds for producing aromatic boron compounds offers an appealing, one-step solution. Despite significant advances in this field, achieving regioselective aryl C-H bond borylation using simple and readily available starting materials still remains a challenge. In this work, we attempted to enhance the reactivity of the electron-donor-acceptor (EDA) complex by selecting different bases to replace the organic base (NEt3) used in our previous research. To our delight, when using NH4HCO3 as the base, we have achieved a mild visible-light-mediated aromatic C-H bond borylation reaction with exceptional regioselectivity (rr > 40:1 to single isomers). Compared with our previous borylation methodologies, this protocol provides a more efficient and broader scope for aryl C-H bond borylation through the use of N-Bromosuccinimide. The protocol's good functional-group tolerance and excellent regioselectivity enable the functionalization of a variety of biologically relevant compounds and novel cascade transformations. Mechanistic experiments and theoretical calculations conducted in this study have indicated that, for certain arenes, the aryl C-H bond borylation might proceed through a new reaction mechanism, which involves the formation of a novel transient EDA complex.

Rational design of super reductive EDA photocatalyst for challenging reactions: a theoretical and experimental study.

We reported a novel electron-donor-acceptor (EDA) photocatalyst formed in situ from isoquinoline, a diboron reagent, and a weak base. To further optimize the efficiency of this photocatalyst, Density Functional Theory (DFT) calculations were conducted to investigate the substituent effects on the properties of vertical excitation energy and redox potential. Subsequently, we experimentally validated these effects using a broader range of substituents and varying substitution positions. Notably, the 4-NH2 EDA complex derived from 4-NH2-isoquinoline exhibits the highest photocatalytic efficiency, enabling feasible metal free borylation of aromatic C-H bond and detosylaion of Ts-anilines under green and super mild conditions. These experimental results demonstrate the effectiveness of our strategy for photocatalyst optimization.

Photoinduced Reduction of Nitroarenes and Tandem C-N Cross-Coupling with Haloarenes.

An efficient photocatalytic C-N cross-coupling of nitroarenes with haloarenes has been developed using simple and cheap Ni(acac)2 as a cocatalyst. The reaction is confirmed as a stepwise process: (1) metal free photoinduced reduction of nitroarenes into aniline derivatives and (2) photo- and Ni-catalyzed C-N cross-coupling of anilines with haloarenes. The reaction conditions are simple and mild, giving high-value diarylamines with good to excellent yields and good functional group tolerance.

Photoinduced metal-free borylation of aryl halides catalysed by an in situ formed donor-acceptor complex.

Organoboron compounds are very important building blocks which can be applied in medicinal, biological and industrial fields. However, direct borylation in a metal free manner has been very rarely reported. Herein, we described the successful direct borylation of haloarenes under mild, operationally simple, catalyst-free conditions, promoted by irradiation with visible light. Mechanistic experiments and computational investigations indicate the formation of an excited donor-acceptor complex with a -3.12 V reduction potential, which is a highly active reductant and can facilitate single-electron-transfer (SET) with aryl halides to produce aryl radical intermediates. A two-step one-pot method was developed for site selective aromatic C-H bond borylation. The protocol's good functional group tolerance enables the functionalization of a variety of biologically relevant compounds, representing a new application of aryl radicals merged with photochemistry.

Direct Synthesis of Bicyclic Acetals via Visible Light Catalysis.

Polysubstituted bicyclic acetals are a class of privileged pharmacophores with a unique 3D structure and an adjacent pair of hydrogen bond acceptors. The key, fused acetal functionality is often assembled, via intramolecular cyclization, from linear substrates that are not readily available. Herein, we report a formal cycloaddition between cinnamyl alcohols and cyclic enol ethers under ambient photoredox catalysis conditions. Polysubstituted bicyclic acetals can be prepared in one step from readily available building blocks. Employment of sugar-derived enol ethers allows easy access to a library of scaffolds with intriguing conformation and medicinal chemistry potential.

Discovery and characterization of an acridine radical photoreductant.

Photoinduced electron transfer (PET) is a phenomenon whereby the absorption of light by a chemical species provides an energetic driving force for an electron-transfer reaction1-4. This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics and photosensitive materials. In recent years, research in the area of photoredox catalysis has enabled the use of PET for the catalytic generation of both neutral and charged organic free-radical species. These technologies have enabled previously inaccessible chemical transformations and have been widely used in both academic and industrial settings. Such reactions are often catalysed by visible-light-absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium or copper5,6. Although various closed-shell organic molecules have been shown to behave as competent electron-transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as excited-state donors or acceptors. This is unsurprising because the lifetimes of doublet excited states of neutral organic radicals are typically several orders of magnitude shorter than the singlet lifetimes of known transition-metal photoredox catalysts7-11. Here we document the discovery, characterization and reactivity of a neutral acridine radical with a maximum excited-state oxidation potential of -3.36 volts versus a saturated calomel electrode, which is similarly reducing to elemental lithium, making this radical one of the most potent chemical reductants reported12. Spectroscopic, computational and chemical studies indicate that the formation of a twisted intramolecular charge-transfer species enables the population of higher-energy doublet excited states, leading to the observed potent photoreducing behaviour. We demonstrate that this catalytically generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and can be used in other organic transformations that require dissolving metal reductants.

Synthesis and Characterization of Acridinium Dyes for Photoredox Catalysis.

Photoredox catalysis is a rapidly evolving platform for synthetic methods development. The prominent use of acridinium salts as a sustainable option for photoredox catalysts has driven the development of more robust and synthetically useful versions based on this scaffold. However, more complicated syntheses, increased cost, and limited commercial availability have hindered the adoption of these catalysts by the greater synthetic community. By utilizing the direct conversion of a xanthylium salt into the corresponding acridinium as the key transformation, we present an efficient and scalable preparation of the most synthetically useful acridinium reported to date. This divergent strategy also enabled the preparation of a suite of novel acridinium dyes, allowing for a systematic investigation of substitution effects on their photophysical properties.

Direct Synthesis of Polysubstituted Aldehydes via Visible-Light Catalysis.

Aldehydes are among the most versatile functional groups for synthetic chemistry. However, access to polysubstituted alkyl aldehydes is very limited and requires lengthy synthetic routes that involve multiple-step functional-group conversion. This paper reports a one-step synthesis of polysubstituted aldehydes from readily available olefin substrates using visible-light photoredox catalysis. Despite a number of competing reaction pathways, commercial styrenes react with vinyl ethers selectively in the presence of an acridinium salt photooxidant and a disulfide hydrogen-atom-transfer catalyst under blue LED irradiation. Alkyl aldehydes with different substitution patterns are prepared in good yields. This strategy can be applied to structurally sophisticated substrates.

Visible-Light-Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives.

We report a formal [4+2] cycloaddition reaction of styrenes under visible-light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo- and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates.

The Intelligent Control System and Experiments for an Unmanned Wave Glider.

The control system designing of Unmanned Wave Glider (UWG) is challenging since the control system is weak maneuvering, large time-lag and large disturbance, which is difficult to establish accurate mathematical model. Meanwhile, to complete marine environment monitoring in long time scale and large spatial scale autonomously, UWG asks high requirements of intelligence and reliability. This paper focuses on the "Ocean Rambler" UWG. First, the intelligent control system architecture is designed based on the cerebrum basic function combination zone theory and hierarchic control method. The hardware and software designing of the embedded motion control system are mainly discussed. A motion control system based on rational behavior model of four layers is proposed. Then, combining with the line-of sight method(LOS), a self-adapting PID guidance law is proposed to compensate the steady state error in path following of UWG caused by marine environment disturbance especially current. Based on S-surface control method, an improved S-surface heading controller is proposed to solve the heading control problem of the weak maneuvering carrier under large disturbance. Finally, the simulation experiments were carried out and the UWG completed autonomous path following and marine environment monitoring in sea trials. The simulation experiments and sea trial results prove that the proposed intelligent control system, guidance law, controller have favorable control performance, and the feasibility and reliability of the designed intelligent control system of UWG are verified.

Ortho-dearomatization of phenols creating all-carbon spiro-bicycles.

A range of alkene-linked phenols are generally and reliably dearomatized specifically at their ortho-positions to create all-carbon quaternary stereogenic centers at the corresponding spiro-ring junctions, thus establishing a viable solution to the long-standing synthetic challenge.