Carbazole/cyanobenzene photocatalysts promote the direct isotopic carboxylate exchange of C(sp 3 )-acids with labelled CO2. Substrates that are not compatible with transition metal catalyzed degradation-reconstruction approaches or prone to thermally induced reversible decarboxylation undergo isotopic incorporation at room temperature in short reaction times. The radiolabelling of drug molecules and precursors with [ 11 C]CO2 is demonstrated.The synthesis of isotopically labelled molecules is essential to drug development and nuclear medicine. As drug candidates move towards clinical research and human trials, absorption, distribution, metabolism, and excretion (ADME) studies require compounds enriched with long-lived radioisotopes like 3 H and 14 C. 1 Positron emission tomography (PET) techniques that probe the advance of disease states and can determine the efficacy of drug treatment require molecular targets radiolabelled with short-lived positron-emitting isotopes such as 11 C or 18 F. 2 The limited availability and high cost of isotopically enriched precursors make the preparation of complex targets challenging. For PET studies, compounds must be synthesized and purified within a few half-lives of the radiolabel ( 11 C t1/2 = 20.3 minutes). Approaches that selectively introduce isotopic labels from feedstock sources with compatibility towards common structural motifs found in clinical candidates will have a positive impact on both drug discovery efforts and medical imaging.Metal-catalyzed 1 H/ 3 H exchange is widely used in drug development to introduce long-lived radiolabels into target molecules. [3][4][5][6][7][8][9] The loss of 3 H labels through (bio)chemical reactions and metabolic shifting due to primary kinetic isotope effects are liabilities of 3 H-labelling approachs. 10-11 ADME tracer compounds with greater stability can be obtained by using 14 C radiolabels. 12 Similarly, 11 C-isotopologues of native bioactive molecules enable PET probe generation without changes to their biological or pharmacological properties. 13 The incorporation of 14 C, 13 C or 11 C (*C) units into drug molecules or precursors by the formation of a *C-C bond is challenging and often requires revised synthetic pathways to introduce the label from *CO, 14-18 *CH3I, [19][20] or other small molecules derived by reduction of *CO2. [21][22][23][24][25] The direct exchange of carboxylate groups with CO2 offers the potential for simple and cost-effective syntheses of C-labelled small molecules, particularly as CO2 (or BaCO3) is the feedstock for all radiolabelled carbon-based precursors. 26 The easy conversion of carboxylic acids into other common functionalities (esters, amides, ketones, alcohols) makes this an attractive tactic for isotope incorporation.The use of redox active hydroxyphthalimide ester substrates in combination with Ni-based mediators and stoichiometric metal reductants enables carboxylate groups to undergo net exchange with CO2 (Fig 1A ). [27][28] These reactions are limited to primary alkyl or cyclic secondary a...

2‐(2’‐Hydroxyphenyl)benzazole (HBX) fluorophores are well‐known excited‐state intramolecular proton transfer (ESIPT) emitters largely studied for their synthetic versatility, photostability, strong solid‐state fluorescence and ability to engineer dual emission, thus paving the way to applications as white emitters, ratiometric sensors, and cryptographic dyes. However, they are heavily quenched in solution, due to efficient non‐radiative pathways taking place as a consequence of the proton transfer in the excited‐state. In this contribution, the nature of the heteroring constitutive of these rigidified HBX dyes was modified and we demonstrate that this simple structural modification triggers major optical changes in terms of emission color, dual emission engineering, and importantly, fluorescent quantum yield. Investigation of the photophysical properties in solution and in the solid state of a series of ethynyl‐TIPS extended HBX fluorophores, along with ab initio calculations demonstrate the very promising abilities of these dyes to act as bright dual‐state emitters, in both solution (even in protic environments) and solid state.

A first series of polyanils were synthesized by a simple condensation between either isomers of phenylenediamine derivatives or 1,3,5-benzenetriamine and 4-(diethylamino)salicylaldehyde, while a second series resulted from the condensation between 4,6-dihydroxyisophthalaldehyde or 2,5-dihydroxyterephthalaldehyde and differently substituted anilines. All these polyanils showed good chelating abilities toward trivalent boron fragments such as BF or BPh to yield the corresponding boranils. The optical properties of these novel fluorophores have been studied both in solution and in the solid-state and show emission wavelengths covering the entire visible spectrum and near-infrared (NIR), depending on molecular structure, substitution, and environment. While faintly fluorescent in solution in their molecular state, some polyanils show typical aggregation-induced emission (AIE) behavior upon addition of increasing amounts of water in THF solution, leading to a sizable enhancement of fluorescence intensity.

Dual solution/solid‐state emissive fluorophores based on a 2‐(2′‐Hydroxyphenyl)benzoxazole (HBO) core bearing one or two ethynyl‐tolyl moieties at different positions were synthesized via an expedite two‐step synthetic procedure. HBO derivatives are known to display intense Excited‐State Intramolecular Proton Transfer (ESIPT) emission in the solid‐state but are mildly emissive in solution due to the detrimental flexibility of the excited‐state opening efficient non‐radiative pathways. The sole introduction of a rigid ethynyl moiety led to a sizeable enhancement of the fluorescence quantum yield in solution, up to a 15‐fold increase in toluene as compared to unsubstituted HBO dyes while keeping the high solid‐state fluorescence efficiency. The position of the substitution on the π‐conjugated core led to subtle fine‐tuning of maximum emission wavelengths and quantum yields. Moreover, we show that the ethynyl tolyl substituent at the para position of the phenol ring is a suitable moiety for an efficient stabilization of the corresponding emissive anionic HBO derivatives in dissociative solvents like DMF THF or EtOH. These observations were confirmed in CH3CN by a basic titration. For all dyes, the nature of the excited‐state involved in the fluorescence emission was rationalized using ab initio calculations.

This article describes the synthesis, spectroscopic studies, and theoretical calculations of nine original fluorophores based on the 2-(2′hydroxyphenyl)benzazole (HBX) scaffold, functionalized at the 4-position of the phenol ring by ethynyl-extended aniline moieties. HBX dyes are wellknown to display an excited-state intramolecular proton transfer (ESIPT) process, owing to a strong six-membered hydrogen bond in their structure that allows for an enol/keto tautomerism after photoexcitation. Appropriate electronic substitution can perturb the ESIPT process, leading to dual fluorescence, both excited tautomers emitting at specific wavelengths. In the examples described herein, it is demonstrated that the proton transfer can be finely frustrated by a modification of the constitutive heteroring, leading to a single emission band from the excited enol or keto tautomer or a dual emission with relative intensities highly dependent on the environment. Moreover, the nature of the functionalization of the N-alkylated aniline moiety also has a significant importance on the relative excited-state stabilities of the two tautomers in solution. To shed more light on these features, quantum chemical calculations by the density functional theory are used to determine the excited-state energies and rationalize the experimental spectroscopic data.

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A synthetic pathway for PET-labeled amides is described using rhodium-catalyzed coupling of organozinc iodide reagents and in situ prepared carbon-11 isocyanates. A scope prepared using carbon-12 isocyanates yielded products from 13-87% using readily prepared sp 3 and sp 2 organozinc iodides. By manipulation of fixation, dehydration, and coupling conditions, the incorporation of [ 11 C]CO2 into 11 C-amide products proceeded in moderate to strong yields, as determined by radioHPLC. Among the compounds prepared are the biologically-relevant tert-butyl protected [ 11 C]N-acetyl glutamic acid ([ 11 C]6d), the agrochemical [ 11 C]propanil ([ 11 C]6f), and a pharmaceutically-relevant [ 11 C]acetanilide ([ 11 C]4m). The synthetic utility of the labeling methodology was demonstrated through the isolation of [ 11 C]N-(4-fluorophenyl)-4-methoxybenzamide ([ 11 C]6g) with a molar activity of 267 GBq•mol -1 and a radioactivity yield of 12%, 21 minutes after beginning of synthesis.

Amine‐functionalized squaramides 1 and 2 were prepared and shown to be suitable polymerization organocatalysts for the controlled ring‐opening polymerization (ROP) of l‐lactide (l‐LA) in the presence of an alcohol source such as BnOH (which acts as an initiator) to afford chain‐length‐controlled and narrow‐dispersion poly(l‐lactide) (PLLA) under mild reaction conditions. The ROP experimental and polymer analysis data are consistent with the action of 1 and 2 as bifunctional hydrogen‐bonding (HB) catalysts that are able to activate both the lactide monomer and initiator BnOH thanks to their dual HB acceptor and donor properties. As a comparison, aminosquaramide 3, a direct analogue of 1 but a weaker HB donor because of the absence of electron‐withdrawing NH substituents, displays little lactide ROP activity, which highlights the key role of monomer activation through HB in the present systems. Unlike aminosquaramides 1 and 2, related monofunctional squaramides 4 and 5 are inactive in l‐LA ROP in the presence of BnOH, but the addition of NEt3, as an external HB acceptor, allows the ROP to proceed with the production of well‐defined PLLA. A cooperative dual activation with an activated monomer/activated chain‐end mechanism is most likely operative in the lactide ROP mediated by 1 and 2 in the presence of BnOH.