Light-induced decarboxylation of (o-acylphenyl)acetic acids

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Synthesis of Isoindoles from Intramolecular Condensation of Benzyl Azides with α-Aryldiazoesters

Rh-catalyzed intramolecular condensation of the benzyl azides with α-aryldiazoesters was explored. The reaction proceeded through the nucleophilic attack of the organic azide onto a rhodium carbenoid, while releasing nitrogen gas, affording the α-imino esters as the primary product. Tautomerization of the imino esters efficiently gave 13 desired isoindoles with good to excellent yields.

Integrated continuous flow/batch protocol for the photoreduction of ortho-methyl phenyl ketones using water as the hydrogen source

The direct hydrogenation of ketones (RRCO) with water to secondary alcohols under catalyst-free, minimal risk conditions, through the light-driven transfer hydrogenation platform.

Ti(Oi-Pr)4-promoted photoenolization Diels-Alder reaction to construct polycyclic rings and its synthetic applications

Stereoselective construction of polycyclic rings with all-carbon quaternary centers, and vicinal all-carbon quaternary stereocenters, remains a significant challenge in organic synthesis. These structures can be found in a wide range of polycyclic natural products and drug molecules. Here we report a Ti(Oi-Pr)₄-promoted photoenolization/Diels–Alder (PEDA) reaction to construct hydroanthracenol and related polycyclic rings bearing all-carbon quaternary centers. This photolysis proceeds under mild conditions and generates a variety of photo-cycloaddition products in good reaction efficiency and stereoselectivity (48 examples), and has been successfully used in the construction of core skeleton of oncocalyxones, tetracycline and pleurotin. It also provides a reliable method for the late-stage modification of natural products bearing enone groups, such as steroids. The total synthesis of oncocalyxone B was successfully achieved using this PEDA approach.

Anthracenols with multiple chiral centres are common motifs in natural products. Here, the authors show a highly stereoselective photoenolization/Diels–Alder methodology involving a key Lewis acid reagent enabling the efficient construction of a family of anthracenol derivatives with quaternary centers.

pH Dependent Photodeprotection of Formaldehyde: Homolytic C-C Scission in Acidic Aqueous Solution versus Heterolytic C-C Scission in Basic Aqueous Solution

The photodeprotection of formaldehyde was investigated for 3-(1-hydroxypropan-2-yl)benzophenone (3-HPBP) with ultrafast time-resolved spectroscopy. The femtosecond transient absorption results indicated the singlet excited state of 3-HPBP transformed efficiently into its triplet state by a fast intersystem crossing. In acidic (pH = 0) and basic (pH = 12.5) aqueous solutions, the triplet intermediate was a key precursor for the deprotection of formaldehyde via two different pathways. However, little photodeprotection was observed in neutral (pH = 7) aqueous solution where the triplet intermediate appeared to undergo a proton coupled electron transfer process to form a ketyl radical transient. The important benzylic biradical intermediates seen in the acidic and basic aqueous solutions were identified by time-resolved resonance Raman spectra whose vibrational frequency patterns were consistent with DFT calculation results for the benzylic biradical intermediate. The results here indicate that the β-carbon alcohol group of the triplet state 3-HPBP is deprotonated in basic aqueous solutions and this leads to a heterolytic C-C bond cleavage to deprotect formaldehyde and produce the benzylic carbanion triplet state species, whereas protonation of the carbonyl moiety of the triplet state 3-HPBP leads to direct generation of a benzylic biradical intermediate and the deprotection of formaldehyde in acidic aqueous solutions via a homolytic C-C bond cleavage.

Unique structural micro-adjustments in a new benzothiadiazole-derived Zn(ii) metal organic framework via simple photochemical decarboxylation

Herein, we report the first exploration of structural micro-adjustments via simple photochemical decarboxylation in a new Zn(ii) benzothiadiazole-derived MOF, Zn-BTDC-M1.

Metal-Free Domino One-Pot Decarboxylative Cyclization of Cinnamic Acid Esters: Synthesis of Functionalized Indanes

Trifluoroacetic acid promoted unprecedented domino reaction for the synthesis of diverse indanes starting from simple cinnamic acid esters is described. Their formation can be explained via acid triggered decarboxylation of cinnamic acid esters and subsequent inter/intramolecular cyclization. Overall process involves in the intramolecular cleavage of two σ-bonds (C-O and C-C) and inter/intramolecular construction of two/one C-C σ-bond(s). Significantly, this protocol was successful without the aid of any metal salts.

Water-assisted self-photoredox of 2-(1-hydroxyethyl)-9,10-anthraquinone through a triplet excited state intra-molecular proton transfer pathway

A novel self-photoredox reaction for 2-(1-hydroxyethyl)-9,10-anthraquinone has been theoretically rationalized to take place through two steps of triplet excited state intra-molecular proton transfer aided by water wires.

Plasmon-induced decarboxylation of mercaptobenzoic acid on nanoparticle film monitored by surface-enhanced Raman spectroscopy

Surface plasmon plays an important role in surface catalysis reactions, and thus the tuning of plasmon on metal nanostructures and the extension of plasmon induced surface catalysis reactions have become important issues.

Manganese(III) Porphyrin Covalently Bound to sol-gel Derived Silica (Mn(III) Porphyrinosilica): A Reusable and Green Heterogeneous Photocatalyst for Oxidative Decarboxylation of α-Arylacetic Acids with H2O2

Manganese(III) (5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin)chloride, MnIII(TDCPP)Cl, was chemically (covalently) bound to a silica matrix by a sol-gel method and used as a new reusable heterogeneous photocatalyt for the selective and efficient oxidative decarboxylation of α-arylacetic acids with H2O2 as a mild and clean oxidant at room temperature. The activity of this heterogeneous photocatalytic system is higher than that of a corresponding homogeneous systems and the catalyst can be reused several times without loss of its activity and selectivity.