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Visible light photocatalysis has evolved into a promising mild and sustainable strategy to access radicals. This field unlocks formerly challenging or even previously inaccessible organic transformations. In this review, an overview of some lesser-known modes of photochemical activation of organic molecules and several emerging techniques within the versatile field of visible light photocatalysis are discussed. These are illustrated by selected photocatalytic reactions, with particular attention given to the reaction mechanism. 1 Introduction 2 Advanced Photoactivation Modes 2.1 Photoinduced Hydrogen-Atom Transfer 2.2 Proton-Coupled Electron Transfer 2.3 Electron Donor-Acceptor Photoactivation of Organic Substrates 2.4 Excited-State Transition Metal Catalysis 3 Emerging Techniques 3.1 Dual Catalysis 3.2 Excited Radical Ion Photocatalysis 3.3 Upconversion Strategies and Other Two-Photon Mechanisms 3.4 Red and Near-Infrared Photocatalysis 4 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

Visible light photocatalysis has established itself as a promising sustainable and powerful strategy to access reactive intermediates, i.e. radicals and radical ions, under mild reaction conditions using visible light irradiation. This field enables the development of formerly challenging or even previously inaccessible organic transformations. In this tutorial review, an overview of the essential concepts and techniques of visible-light-mediated chemical processes and the most common types of photochemical activation of organic molecules, i.e. photoredox catalysis and photosensitization, are discussed. Selected photocatalytic alkene functionalization reactions are included as examples to illustrate the basic concepts and techniques with particular attention given to the understanding of their reaction mechanisms. 1 Introduction 2 Photocatalysts 3 Photophysical and Electrochemical Properties 3.1 Excited-State Energy 3.2 Ground-State Redox Potentials 3.3 Excited-State Redox Potentials 3.4 Local Absorbance Maximum for Lowest Energy Absorption 3.5 Excited-State Lifetime 3.6 [Ru(bpy)3 ]2+ as a Case Study 3.7 Basic Laws and Equations of Photochemistry and Photocatalysis 3.8 Common Terminology in Photochemistry and Photocatalysis 4 Activation Modes in Photocatalysis 4.1 Photoinduced Electron Transfer 4.2 Photoinduced Energy Transfer 5 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

Calcium carbide was used in a CuI‐catalysed three‐component coupling with ω‐chlorinated ketones and primary amines to generate terminal 2‐alkynyl‐N‐heterocycles. The formation of an imine and the subsequent intramolecular substitution results in an active electrophilic iminium species, which can be alkynylated by in situ formed copper acetylide. A number of aliphatic primary (functionalised) amines and aliphatic or aromatic alkynes together with different alkyl‐ or aryl‐substituted γ‐ or δ‐chloroketones could be used. Simple acid–base workup instead of column chromatography can be applied to obtain the resulting 2‐alkynylpyrrolidines and 2‐alkynylpiperidines. Three strikes: Calcium carbide can be used as an acetylene source through in situ hydrolysis. It was used in a three‐component coupling with ω‐chlorinated ketones and primary amines rendering terminal cyclic propargyl amines (see scheme). [ABSTRACT FROM AUTHOR]

Azidation of indoles using iodine and copper bromide as catalysts under ambient reaction conditions is presented. The regioselectivity is directed by the substituent at the C3-position of indole. A radical stabilizing group such as an ester or ketone moiety at the C3-position of indole leads to azidation at the C2-position, whereas a less radical stabilizing group such as an alkyl or amide group at the C3-position of indole furnishes the 3-azidooxindole product. This protocol is mild and efficient to obtain several 2-azidoindole derivatives and 3-azidooxindole derivatives in moderate to good yields. The reaction conditions hold well for gram-scale synthesis. [ABSTRACT FROM AUTHOR]

A palladium-boronate/borane-system-catalyzed isomerization of olefins has been uncovered. An efficient catalytic combination of [Pd(OAc)2]3-boronate-PCy3-enabled olefin isomerization at 80 °C has been investigated. Addition of water to the reaction showed a remarkable improvement and the isomerization occurred at ambient temperature. These catalytic systems function efficiently for the isomerization of functionalized as well as unfunctionalized olefins. The catalytic conditions demonstrate the involvement of both nonhydride and metal-hydride medium and can be switchable with water as an additive. [ABSTRACT FROM AUTHOR]

Production of hydrogen from renewable sources, particularly from water, is an intensive area of research, which has far-reaching relevance in hydrogen economy. A homogeneous catalytic method is presented for producing clean hydrogen gas from water, in a reaction of water with a diboron compound as the reductant, under ambient reaction conditions. The Pd-catalytic system is stable in water and displays excellent recyclability. Hydroxy analogues such as alcohols are compatible with the Pd/B2Pin2 system and generate hydrogen gas efficiently. The B2Pin2-H2O system, in the presence of palladium, is an excellent catalytic system for selective hydrogenation of olefins. [ABSTRACT FROM AUTHOR]

Sulfenylation of β-diketones is challenging as β-diketones undergo deacylation after sulfenylation in the reaction medium. The sulfenylation of β-diketones without deacylation under metal-free conditions at ambient temperature via a cross dehydrogenative coupling (CDC) strategy is reported. The resultant products can be further manipulated to form a,a-disubstituted β-diketones and pyrazoles. [ABSTRACT FROM AUTHOR]

A mild and convenient method for the synthesis of amides has been explored by using secondary alcohols, Cu(ClO4)2·6H2O as a catalyst, and trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) at ambient temperature. This method has been successfully adapted to the preparation of azides directly from their corresponding alcohols and offers excellent chemoselectivity in the formation of ω-halo azides and the azidation of allylic alcohols in the presence of a benzyl alcohol moiety. In addition, this strategy provides an opportunity to synthesize azides that can serve as precursors to β-amino acids. [ABSTRACT FROM AUTHOR]

A mild and convenient oxidative transformation of secondary alcohols to 1,5-disubstituted tetrazoles is uncovered by employing trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of a catalytic amount of copper(II) perchlorate hexahydrate [Cu(ClO4)2.6 H2O] (5 mol%) and 2,3-dichloro-5,6-dicyano- para-benzoquinone (DDQ) (1.2 equiv.) as an oxidant. This reaction is performed under ambient conditions and proceeds through CC bond cleavage. [ABSTRACT FROM AUTHOR]

A metal-free, convenient one-step strategy is presented proceeding at ambient temperature via a cross-dehydrogenative coupling of benzoxazole-thiones or bis(benzothiazoyl)disulfides. [ABSTRACT FROM AUTHOR]

The scalable, mild, and metal-free sulfenylation of 1,3-dialkyl, 1,3-diaryl, or 1,3-alkylaryl substituted β-diketones with various benzoxazole-2-thiones or benzothiazole-2-thiones proceeds without deacylation. [ABSTRACT FROM AUTHOR]

A one-pot formation of azides from allylic alcohols (I) and (III) followed by Cu(II)-perchlorate and DDQ mediated azide decomposition results in the direct synthesis of diarylamides. [ABSTRACT FROM AUTHOR]

A mild and convenient protocol using TmsN3 as a nitrogen source is developed for the conversion of cinnamyl and benzyl alcohols into disubstituted tetrazoles. [ABSTRACT FROM AUTHOR]