Tetrabutylammonium decatungstate (TBADT), a compelling and trailblazing catalyst for visible-light-induced organic photocatalysis.

Tetrabutylammonium decatungstate (TBADT) has recently emerged as an intriguing photocatalyst under visible-light or near-visible-light irradiation in a wide range of organic reactions that were previously not conceivable. Given its ability to absorb visible light and excellent effectiveness in activating unactivated chemical bonds, it is a promising addition to traditional photocatalysts. This review covers some of the contemporary developments in visible-light or near-visible-light photocatalysis reactions enabled by the TBADT catalyst to 2023, with the contents organized by reaction type.

From citronellal to iridoids: asymmetric synthesis of iridoids and their analogues via organocatalytic intramolecular Michael reactions.

A series of iridoids, including iridomyrmecin A, B, C', D', (-)-isoiridomyrmecin, (+)-7-epi-boschnialactone, and the inside-yohimbine analogues have been synthesized from readily available, naturally occurring (-)-citronellal via the key step reaction of metathesis, organocatalysis, and subsequent transformations, such as reduction, lactonization, alkylation, Pictet-Spengler reaction and lactamization. Notably, the use of DBU as an additive in the organocatalytic intramolecular Michael reaction of an aldehyde ester with Jørgensen-Hayashi catalysts resulted in better stereoselectivity than the conditions using acetic acid as an additive. The structures of three products have been unequivocally established with single-crystal X-ray crystallographic analyses.

The hamburger-shape photocatalyst: thioxanthone-based chiral [2.2]paracyclophane for enantioselective visible-light photocatalysis of 3-methylquinoxalin-2(1H)-one and styrenes.

A new thioxanthone-based photocatalyst with a [2.2]paracyclophane skeleton and planar chirality has been developed. The catalyst has been successfully applied in the visible light-mediated enantioselective aza Paternò-Büchi reactions of quinoxalinone and styrenes to produce azetidines. The structures of the catalyst derivatives were unequivocally determined by their single crystal X-ray crystallography analysis.

A mild one-pot transformation of nitroalkanes to ketones or aldehydes via a visible-light photocatalysis-hydrolysis sequence.

Using a visible-light photoredox catalysis strategy with household decorative blue LEDs and the additives Et3N and DIPEA, as well as the subsequent hydrolysis sequence, a mild one-pot process for the direct transformation of nitroalkanes to the corresponding ketones and aldehydes, constituting a Nef-like reaction, has been developed. It is worth noting that by using an appropriate photocatalyst (e.g., [Ir(dtbbpy)(ppy)2]PF6) and the extra additive Et3N with the combination of DIPEA and Mg(ClO4)2 in i-PrOH (instead of CH3CN), the transformation of nitroalkanes to the corresponding oximes, rather than nitrones, can be markedly more effective. The oximes can then be hydrolyzed to ketones by reaction with CuCl2·2H2O in a pH 7 buffer solution. This process is appealing because of the benefits of efficient conversion, mild conditions, high yields, and general applicability to compounds with a wide range of labile functional groups.

Enantioselective synthesis enabled by visible light photocatalysis.

Enantioselective photoreaction has been a synthetic challenge for decades. With the continuous development of modern visible light photocatalysis and asymmetric catalysis, remarkable advances have been achieved through the synergistic action of these catalytic reactions, allowing the construction of various enantiomerically enriched molecules that were once inaccessible using photocatalytic reactions. This review presents some of the contemporary developments in enantioselective visible-light photocatalysis reactions, covering the period from 2008 to March 2020, with the contents classified by catalysis type.

Oxidative trimerization of indoles via water-assisted visible-light photoredox catalysis and the study of their anti-cancer activities.

Incorporation of water has been revealed to successfully facilitate visible-light photoredox catalysis of indole leading to increased production of C2-quaternary indolinone. The water-promoted photoreaction of indole under catalyst-free conditions by a household compact fluorescence light was also demonstrated. The antiproliferative activity of the synthesized indolinones was evaluated against three human cancer cell lines.

Enantioselective Synthesis of Yohimbine Analogues by an Organocatalytic and Pot-Economic Strategy.

An efficient and one-pot method has been developed for the enantioselective synthesis of pentacyclic indole derivatives with the yohimbane skeleton via a sequence of asymmetric Michael-Michael-Mannich-reduction-amidation-Bischler-Napieralski-reduction reactions with a high diastereoselectivity and high enantioselectivities (up to >99% ee). The seven-step reaction sequence, which generates five bonds and five stereocenters, can be conducted with a pot-economic synthetic strategy and one-pot operation in good yields. The structure and absolute stereochemistry of two products were confirmed by X-ray crystallography analysis.

The azatryptophan-based fluorescent platform for in vitro rapid screening of inhibitors disrupting IKKß-NEMO interaction.

The nuclear factor-κB (NF-κB) plays an important role in inflammatory and immune responses. Aberrant NF-κB signaling is implicated in multiple disorders, including cancer. Targeting the regulatory scaffold subunit IκB kinase γ (IKKγ/NEMO) as therapeutic interventions could be promising due to its specific involvement in canonical NF-κB activation without interfering with non-canonical signaling. In this study, the use of unnatural amino acid substituted IKKß with unique photophysical activity to sense water environment changes upon interaction with NEMO provides a powerful in vitro screening platform that would greatly facilitate the identification of compounds having the potential to disrupt IKKß-NEMO interaction, and thus specifically modulate the canonical NF-κB pathway. We then utilized a competitive binding platform to screen the binding ability of a number of potential molecules being synthesized. Our results suggest that a lead compound (-)-PDC-099 is a potent agent with ascertained potency to disrupt IKKß-NEMO complex for modulating NF-κB canonical pathway.

Organocatalytic Enantioselective Michael-Acetalization-Henry Reaction Cascade of 2-Hydroxynitrostyrene and 5-Oxohexanal for the Entry to the Hexahydro-6H-benzo[c]chromenones with Four Consecutive Stereogenic Centers and an Approach to Aflatoxin Analogues.

A domino reaction with the organocatalytic enantioselective Michael-acetalization-Henry reaction of 2-hydroxynitrostyrene and 5-oxohexanal was developed for the synthesis of hexahydro-6H-benzo[c]chromenones with four consecutive stereogenic centers and high enantioselectivity (up to >99% ee). The transformation of a NaBH4-reduced adduct to the aflatoxin system via the Nef-cyclization process was achieved by the assistant of ZnBr2.

Enantioselective total synthesis of (+)-arborescidine C and related tetracyclic indole alkaloids using organocatalysis.

A concise and enantioselective synthesis of the tetracyclic indoles, including the naturally occurring compounds (+)-arborescidine C and (+)-arborescidine B, was achieved by the key step of Pictet-Spengler cyclization reaction with a Jacobsen-type thiourea organocatalyst. The synthetic process was further demonstrated in a pot-economy strategy and was achieved in a one-pot operation.

Locked ortho- and para-core chromophores of green fluorescent protein; dramatic emission enhancement via structural constraint.

We report the design strategy and synthesis of a structurally locked GFP core chromophore p-LHBDI, its ortho-derivative, o-LHBDI, and H2BDI possessing both para- and ortho-hydroxyl groups such that the inherent rotational motion of the titled compounds has been partially restricted. o-LHBDI possesses a doubly locked configuration, i.e., the seven-membered ring hydrogen bond and five-membered ring C(4-5-10-13-14) cyclization, from which the excited-state intramolecular proton transfer takes place, rendering a record high tautomer emission yield (0.18 in toluene) and the generation of amplified spontaneous emission. Compared with their unlocked counterparts, a substantial increase in the emission yield is also observed for p-LHBDI and H2BDI in anionic forms in water, and accordingly the structure versus luminescence relationship is fully discussed based on their chemistry and spectroscopy aspect. In solid, o-LHBDI exhibits an H-aggregate-like molecular packing, offers narrow-bandwidth emission, and has been successfully applied to fabricate a yellow organic light emitting diodes (λmax = 568 nm, ηext = 1.9%) with an emission full width at half-maximum as narrow as 70 nm.

Visible-Light-Photocatalyzed Self-Cyclopropanation Reactions of Dibenzoylmethanes for the Synthesis of Cyclopropanes.

A new self-cyclopropanation of 1,3-diphenylpropane-1,3-dione, leading to tetrasubstituted cyclopropane containing three contiguous stereogenic centers with high stereoselectivity, has been achieved through violet-light-emitting diode-irradiated photocatalysis, featuring both cycloaddition and a distinctive rearrangement. Diverging from conventional cyclopropanation pathways, this reaction yields a tetrasubstituted cyclopropane through unprecedented rearrangement and cascade reactions.

Stereoselective Cyclization Cascade of Dihydroquinoxalinones by Visible-Light Photocatalysis: Access to the Polycyclic Quinoxalin-2(1H)-ones.

An intriguing stereoselective visible-light photocatalysis of dihydroquinoxalinone derivatives has been realized via cyclization with or without the solvolysis cascade. The reactions provided the polycyclic ring structures with efficient formation of multiple bonds and with high stereoselectivity. X-ray crystallography unequivocally determined the structures of five polycyclic products.

Total Synthesis of Ulodione A via a Double-Alkylation and DABCO Promoted Ring-Expansion Rearrangement Sequence.

First total synthesis of ulodione A has been achieved via the key-step reactions of DIPEA-promoted dialkytion of 1,3-cyclopentadione with a bromonitroolefin and DABCO promoted/catalytic semipinacol-like ring-expansion rearrangement, with regioselective transformation of the nitrocyclohexane intermediates to their cyclopentenone counterparts via a sequence of reactions in a one-pot operation. Structures of six products were unequivocally established by X-ray crystallography.

Enantioselective organocatalytic domino Michael-acetalization-Henry reactions of 2-hydroxynitrostyrene and aldehyde for the synthesis of tetrahydro-6H-benzo[c]chromenones.

Asymmetric domino Michael-acetalization reactions of 2-hydroxynitrostyrene and aldehydes "on water" followed by oxidation providing the cis-3,4-disubstituted dihydrocoumarins with excellent enantioselectivities (up to >99% ee). The variant with glutaraldehyde underwent a highly stereoselective domino Michael-acetalization-Henry reaction to afford the tetrahydro-6H-benzo[c]chromen-6-ones after the subsequent oxidation.

Control of the Organocatalytic Enantioselective α-Alkylation of Vinylogous Carbonyl Enolates for the Synthesis of Tetrahydropyran Derivatives and Beyond.

The organocatalytic α-alkylation of vinylogous carbonyl compounds to hydroxynitroolefins for the synthesis of hemiacetals was realized with excellent enantioselectivities and in high yields. High diastereoselectivity (up to >20:1) has been accomplished with the addition of Et3N. The α- and γ-alkylation of vinylogous ketone against nitroolefins displayed high but opposite facial selectivities. Transformation of the hemiacetal products to other polycyclic compounds, including the euroticin B analog, has been demonstrated.

Catalytic 1,2-Rearrangements: Organocatalyzed Michael/Semi-Pinacol-like Rearrangement Cascade of 1,3-Diones and Nitroolefins.

New types of organocatalytic 1,2-rearrangements, which resemble the Smiles-like or semi-pinacol-like rearrangement, of Michael adducts of 1,3-dicarbonyl-2-alkyl compounds and nitroalkenes have been realized. Unlike the well-known conjugate addition, the reaction affords the 1-phenyl-1-nitroalkanes via unprecedented rearrangement and cascade reactions. Structures of the appropriate products were unambiguously characterized by X-ray crystallography.

Asymmetric Synthesis of Spirocyclopentane Oxindoles Containing Four Consecutive Stereocenters and Quaternary α-Nitro Esters via Organocatalytic Enantioselective Michael-Michael Cascade Reactions.

An enantioselective domino Michael-Michael reaction of nitroolefins and 2-nitro-3-arylacrylates has been established, which provided a series of spirocyclopentane oxindoles with four consecutive stereocenters including quaternary α-nitro esters with good yields (up to 73%) and excellent enantioselectivities (up to 97% ee). The reaction was realized and optimized with the aid of a chiral squaramide-amine catalyst. The structures of 11 products were confirmed by single-crystal X-ray diffraction analysis.

Direct Transformation of Nitroalkanes to Nitriles Enabled by Visible-Light Photoredox Catalysis and a Domino Reaction Process.

A mild and convenient process for direct transformation of nitroalkanes to the corresponding nitriles was developed using a visible-light photoredox catalysis strategy with household decorative blue LEDs and the additives of Et3N and DIPIBA (or DIPEA). Application of the process in secondary nitroalkanes bearing a ß-alcohol resulted in a domino process of the retro-Henry reaction and the subsequent acetalization, aldol, cyanohydrin, and ring-contraction reactions with stereoselectivities. The photocatalytic reaction was demonstrated by a continuous flow method.

Organocatalytic enantioselective domino Michael-aldol condensation of 5-oxoalkanal and alpha,beta-unsaturated aldehydes. Efficient assembly of densely functionalized cyclohexenes.

Organocatalytic Michael reaction of glutaraldehyde and 3-arylpropenal followed by the subsequent intramolecular aldol condensation provided 2-arylcyclohex-3-ene-1,3-dicarbaldehydes. Reactions with the 5-oxohexanal variant afforded the highly functionalized cyclohexenedicarbaldehydes in high diastereoselectivity and high enantioselectivity (>99% ee). Structure of the adduct 3j was confirmed unambiguously by X-ray analysis.