In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

Asymmetric enamine catalysis.

Reactions that convert carbon–hydrogen (C–H) bonds into carbon–carbon (C–C) or carbon–heteroatom (C–Y) bonds are attractive tools for organic chemists, potentially expediting the synthesis of target molecules through new disconnections in retrosynthetic analysis. Despite extensive inorganic and organometallic study of the insertion of homogeneous metal species into unactivated C–H bonds, practical applications of this technology in organic chemistry are still rare. Only in the past decade have metal-catalyzed C–H functionalization reactions become more widely utilized in organic synthesis.Research in the area of homogeneous transition metal–catalyzed C–H functionalization can be broadly grouped into two subfields. They reflect different approaches and goals and thus have different challenges and opportunities. One approach involves reactions of completely unfunctionalized aromatic and aliphatic hydrocarbons, which we refer to as “first functionalization”. Here the substrates are nonpolar and hydrophobic a...

Weak coordination as a powerful means for developing broadly useful C-H functionalization reactions.

Small-molecule H-bond donors in asymmetric catalysis.

The stereoselective route to the title insect hormones (JH-1 & JH-2) depends crucially on the epoxidation of allylic alcohols with t-butyl hydroperoxide in the presence of oxobis(2,4-pentanedionato-O,O′)vanadium(IV). The oxidation of 2-methyl-1-hepten-3-ol exclusively produces the (2R*,3S*) isomerofthe diastereomeric epoxy alcohols. This is converted into (Z)-6-methyl-5-undecene by the sequence involving oxirane reaction with lithium dibutylcuprate(I) and the removal of both hydroxyl groups of the resulting 1,2-diol. Extension of the series of reactions to the mono- and bisoxirane derived from (E,E)-farnesol gives JH-2 and JH-1, respectively.

Syntheses of cecropia juvenile hormones by selective side-chain methylation of (E,E)-farnesol.

Direct asymmetric synthesis of N-chiral amine oxides was accomplished (up to 91:9 e.r.) by means of a bimetallic titanium catalyst. A hydroxy group situated at the γ-position of the N stereocenter enables the desired N-oxidation through dynamic kinetic resolution of the trivalent amine substrates. The method was further extended to the kinetic resolution of racemic γ-amino alcohols with a preexisting stereocenter, giving an important class of enantioenriched (up to 99.9:0.1 e.r.) building blocks that are otherwise difficult to synthesize.

Hisashi Yamamoto

Papers

Syntheses of cecropia juvenile hormones by selective side-chain methylation of (E,E)-farnesol.

Catalytic Asymmetric Synthesis of N-Chiral Amine Oxides.

First enantioselective protonation of prochiral allyltrimethyltins using lewis acid assisted chiral bronsted acids

A simple synthesis of α-haloketones via β-oxido carbenoids

Stereospecific annulation of hydroxy vinyl ethers. Synthetic application to polyfunctionalized cyclic compounds