An unprecedented phototandem catalysis based on a single iridium photocatalyst has been successfully developed. This powerful strategy consists of two mechanistically distinct catalytic cycles, namely, photocatalytic energy transfer (ET) and single electron transfer (SET). The novel protocol allows a rapid and efficient construction of biologically and synthetically important 3-ester-3-hydroxy-2-oxindole derivatives from readily available diazoamides through a cyclization/aerobic oxidation sequence under very mild conditions.

A novel and efficient CP bond formation reaction of diarylphosphine oxides with aryl iodides was achieved by combining nickel catalysis and visible-light-induced photoredox catalysis. This dual-catalytic reaction showed a broad substrate scope, excellent functional group tolerance, and afforded the corresponding products in good to excellent yields. Compared with the previously reported use of photoredox/nickel dual catalysis in the construction of CC bonds, the methodology described herein was observed to be the first to allow for C-heteroatom bond formation.

An unprecedented α-allylation of amines was achieved by combining palladium catalysis and visible-light photoredox catalysis. In this dual catalysis process, the catalytic generation of allyl radical from the corresponding π-allylpalladium intermediate was achieved without additional metal reducing reagents (redox-neutral). Various allylation products of amines were obtained in high yields through radical cross-coupling under mild reaction conditions. Moreover, the transformation was applied to the formal synthesis of 8-oxoprotoberberine derivatives which show potential anticancer properties.

A sequential one-pot Cu-catalyzed asymmetric Henry reaction and iodocyclization is disclosed. The transformation provides efficient access to biologically and synthetically useful 2,2,5-trisubstituted tetrahydrofuran derivatives. The combination of Cu(OAc)₂·H₂O with a novel chiral sulfoxide–Schiff base hybrid ligand under mild reaction conditions tolerates a wide range of 4-substituted γ,δ-unsaturated aldehydes, and the subsequent iodocyclization furnishes the corresponding products in generally high yields with excellent enantioselectivities. The products can be easily converted into amines with excellent diastereo- and enantioselectivities.

An efficient halocyclization of β,γ-unsaturated hydrazones with N-bromosuccinimide was developed without the addition of any additives under mild reaction conditions to provide facile access to biologically important 4,5-dihydropyrazoles. Under the optimized conditions, a variety of highly substituted 4,5-dihydropyrazole derivatives were obtained in generally good yields. Moreover, this reaction can be further applied to the synthesis of pyrazoles in a one-pot fashion.

A photocatalytic formal [3+2] cycloaddition of 2H-azirines with alkynes has been achieved under irradiation by visible light in the presence of organic dye photocatalysts. This transformation provides efficient access to highly functionalized pyrroles in good yields and has been applied to the synthesis of drug analogues. A primary trial of photocascade catalysis merging energy transfer and redox neutral reactions was shown to be successful.

A novel method for the synthesis of 1,4-diketones from β-ketosulfones was developed by means of a visible light-induced CS bond activation process. Symmetrical and unsymmetrical 1,4-diketones can be easily prepared in moderate to good yields.

An unprecedented Zn(OTf)₂-catalyzed asymmetric Michael addition/cyclization cascade of 3-nitro-2H-chromenes with 3-isothiocyanato oxindoles has been disclosed. This transformation provides an efficient access to various synthetically important polycyclic spirooxindoles in a highly stereoselective manner under mild conditions (72–99 % yields, up to >95:5 d.r. and >99 % ee). The reaction leads to the formation of three consecutive stereocenters, including 1,3-nonadjacent tetrasubstituted carbon stereocenters, in a single operation. A bifunctional activation model of the chiral Zn(OTf)₂/bis(oxazoline) complex was proposed based on control experiments, wherein the Zn^II moiety serves as a Lewis acid and the N atom of the free NH group acts as a Lewis base by a hydrogen-bonding interaction.

A visible-light photocatalytic generation of N-centered hydrazonyl radicals has been accomplished for the first time. This approach allows efficient intramolecular addition of hydrazonyl radical to terminal alkenes, thus providing hydroamination and oxyamination products in good yields. Importantly, the protocol involves deprotonation of an NH bond and photocatalytic oxidation to an N-centered radical, thus obviating the need to prepare photolabile amine precursors or the stoichiometric use of oxidizing reagents.

A visible light-induced, aerobic oxyamidation reaction of indoles, using air as the sole oxidant, has been developed. This process serves as a photocatalytic strategy to generate efficiently tetrahydro-5H-indolo[2,3-b]quinolinols, which may have interesting biological and pharmacological activities owing to their privileged indoline structure.

Carbocyclic and heterocyclic ring systems are important structural architectures in many bioactive natural products, as well as in a variety of fine chemicals. The utilization of visible-light photocatalytic strategies to construct these ring systems has received considerable attention in the past few years. This microreview presents a brief summary of the use of visible-light photoredox catalytic strategies for the synthesis of carbocyclic and heterocyclic targets.

A formal [3+2] cycloaddition involving the organocatalytic asymmetric Michael addition/cyclization cascade reaction of ylideneoxindoles with isothiocyanato oxindoles was developed. This method allows efficient and rapid synthesis of highly functionalized bispirooxindole products bearing three contiguous stereogenic centers with two quaternary stereocenters in almost quantitative yields with extremely high enantio- and diastereoselectivities.

Organische Umsetzungen, die durch sichtbares Licht ausgelöst werden, finden seit einigen Jahren immer größere Aufmerksamkeit. Insbesondere im Hinblick auf Kosten, Sicherheit, Verfügbarkeit und Umweltfreundlichkeit ist die Entwicklung solcher photokatalytischer Reaktionen zur effizienten Herstellung von Feinchemikalien höchst wünschenswert. In diesem Kurzaufsatz werden die jüngsten Fortschritte auf diesem sich schnell entwickelnden Forschungsgebiet erörtert.

A hydrogen-bond-mediated asymmetric [4+1] annulation/rearrangement cascade of stable sulfur ylides and nitroolefins was developed. This reaction provides a facile route to enantioenriched 4,5-substituted oxazolidinones in moderate to excellent isolated yields (65–96 %) with excellent stereocontrol (up to more than 95:5 d.r. and 97:3 e.r.). This methodology was successfully applied to the concise synthesis of two bioactive molecules. The stereocontrolled modes and mechanism have been proposed to explain the origin of this stereochemistry.

In the last few years, visible-light initiated organic transformations have attracted increasing attention. The development of visible-light-promoted photocatalytic reactions, which enable rapid and efficient synthesis of fine chemicals, is highly desirable from the viewpoint of cost, safety, availability, and environmental friendliness. In this Minireview, recent advances made in this fast developing area of research are discussed.

A novel cascade Friedel–Crafts alkylation/Michael addition/aromatization reaction of 2-vinylindoles with α,β-unsaturated aldehydes has been developed for the construction of functionalized tetrahydrocarbazoles. The products were obtained in up to 97% yield and with excellent stereoselectivities (ee up to>99%, dr up to>99:1).

A highly efficient and enantioselective intramolecular crossed Rauhut–Currier (RC) reaction of nitroolefins with tethered enonates has been developed through cooperative nucleophilic activation and a hydrogen-bonding catalytic strategy (≤98 % ee and 98 % yield). The reaction features simple experimental procedures and is completely chemoselective and atom-economic in character. The potential synthetic applications have been demonstrated by the conversion of the RC reaction products into biologically and pharmaceutically valuable compounds with highly diastereoselectivity. In addition, computational investigations were employed to support the proposed mechanism and to obtain a good understanding of the origin of the stereoselectivity in RC reactions.

An efficient, one-pot, multicomponent reaction of aldehydes 1, p-methoxyaniline (2a), and 2-vinylindoles 3 was developed. This approach provides a practical approach to synthetically and biologically significant tetrahydro-γ-carboline and tetrahydroquinoline derivatives in good yields through a chemo- and regioselectivity switch, which can be tuned by simply changing the substituent on the indole component under identical reaction conditions.

The scope of the novel ruthenium-catalyzed tandem cross-metathesis/intramolecular-hydroarylation sequence is described. This methodology offers a practical and efficient synthesis of structurally diverse and complex tetrahydrocarbazoles in good to excellent yields (up to 98 %). Moreover, preliminary efforts towards the development of an enantioselective version of the current process by sequential catalysis with ruthenium complex and chiral amine are presented, with high yields and enantioselectivities (up to 88 % yield and 91 % ee).

Organocatalytic enantioselective synthesis of α-indolyl phosphonates has been successfully carried out via asymmetric Friedel-Crafts alkylation of substituted indoles with (E)-dialkyl 3-oxoprop-1-enylphosphonates in 48–82% yield and 73–96% ee. Chirality, 2009. © 2008 Wiley-Liss, Inc.