Enantioselective Aminocatalytic [2 + 2] Cycloaddition through Visible Light Excitation

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: https://pubs.acs.org/doi/full/10.1021/acscatal.0c01413An asymmetric aminocatalytic activation strategy to obtain enantioenriched cyclobutanes through [2 + 2] photocycloaddition under visible light irradiation is presented. This metal-free process does not require the use of any external photocatalyst, as it is catalyzed by a simple diamine which, upon condensation with an enone substrate, forms an iminium ion intermediate that absorbs in the visible light region. The direct excitation of such an intermediate leads to a charge transfer (CT) excited state that unlocks a stereocontrolled intermolecular photocycloaddition with good enantiomeric and diastereoisomeric ratios and high yields. Finally, DFT calculations and experiments were performed to support the charge transfer behavior and the mechanistic proposalFinancial support was provided by the European Research Council (ERC-CoG, Contract No. 647550), the Spanish Government (RTI2018-095038–B-I00), “Comunidad de Madrid”, and European Structural Funds (S2018/NMT-4367

Predesigned covalent organic frameworks as effective platforms for Pd(II) coordination enabling cross-coupling reactions under sustainable conditions

The phenanthroline unit in an imine-based covalent organic framework (Phen-COF) offers a robust coordination site for Pd(OAc)2 centers. Coordination of palladium centers is demonstrated by a variety of techniques, including X-ray photoelectron spectroscopy and total X-ray fluorescence. The stable phenanthroline-Pd(II) coordination avoids leaching of metal centers to the reaction medium, where deactivation processes through nanoparticle formation limits the catalytic activities observed for homogeneous systems. Thus, because of isolation and immobilization of catalytic sites in the Pd@Phen-COF the performance of material, the catalytic outputs are dramatically increased with respect to the performance observed for analogous molecular catalysts. This concept is applied in this work to C-C cross-coupling reactions under mild and environmentally benign conditions. The activities found for Suzuki-Miyaura and Mizoroki-Heck reactions allow thousands of turnover numbers in the transformation of a wide scope of precursors with a high degree of recyclability. The results reported in this work contribute to the design of greener protocols for transformations that have a crucial role in the industrial synthesis of high-added value fine chemical

Visible light mediated photocatalytic [2 + 2] cycloaddition/ring-opening rearomatization cascade of electron-deficient azaarenes and vinylarenes

The broad presence of azaarene moieties in natural products has promoted the development of new functionalization reactions, giving access to larger libraries of bioactive compounds. The light promoted [2+ 2] photocycloaddition reaction to generate cyclobutanes has been extensively studied in photochemistry. In particular, De Mayo reported the [2 + 2] cycloaddition followed by retroaldol condensation between enols of 1,3-dicarbonyls and double bonds to synthesize 1,5-dicarbonyls. Herein, we describe the [2 + 2] photocycloaddition followed by a ring-opening rearomatization reaction between electron-deficient 2-methylene-azaarenes and double bonds, taking advantage of the ability of these heterocyclic derivatives to form the corresponding pseudo-enamine intermediate. The procedure shows a high functional group tolerance either on the double bond or the heteroarene side and allows the presence of different electron-withdrawing groups. In addition, the wide applicability of this reaction has been demonstrated through the late-stage derivatization of several natural products. Photochemical studies, together with theoretical calculations, support a mechanism involving the photosensitization of the pseudo-enamine intermediateWe acknowledge the financial support from the Spanish Government (RTI2018–095038-B-I00), CAM_UAM (SI1/PJI/2019-00237), CCC-UAM (computing time), and ERC (ERC-CG, 647550). The authors also wish to thank the ‘Comunidad de Madrid’ and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367

Stabilized Chiral Organic Material Containing BINAP Oxide Units as a Heterogeneous Asymmetric Organocatalyst for Allylation of Aldehydes

Condensation of BINAPO-(PhCHO)2 and 1,3,5- tris(4-aminophenyl)benzene (TAPB) results in a new imine-based chiral organic material (COM) that can be further postfunctionalized through reductive transformation of imine linkers to amines. While the imine-based material does not show the necessary stability to be used as a heterogeneous catalyst, the reduced amine-linked framework can be efficiently employed in asymmetric allylation of different aromatic aldehydes. Yields and enantiomeric excesses found are comparable to those observed for the molecular BINAP oxide catalyst, but importantly, the aminebased material also permits its recyclabilityFinancial support was provided by the Spanish Government (PID2019-110637RB-I00). A.L.-M. thanks UAM for a FPIUAM predoctoral fellowship. M.S.-F. thanks Ministerio de Ciencia e Innovación for a FPI contract (PRE2020-092295). A.M. acknowledges the Spanish Government and the European Union through the Funds Next Generation through grant Maria Zambrano-UAM (CA3/RSUE/2021-00648

Recent Advances in the Use of Covalent Organic Frameworks as Heterogenous Photocatalysts in Organic Synthesis

Organic photochemistry is intensely developed in the 1980s, in which the nature of excited electronic states and the energy and electron transfer processes are thoroughly studied and finally well-understood. This knowledge from molecular organic photochemistry can be transferred to the design of covalent organic frameworks (COFs) as active visible-light photocatalysts. COFs constitute a new class of crystalline porous materials with substantial application potentials. Featured with outstanding structural tunability, large porosity, high surface area, excellent stability, and unique photoelectronic properties, COFs are studied as potential candidates in various research areas (e.g., photocatalysis). This review aims to provide the state-of-the-art insights into the design of COF photocatalysts (pristine, functionalized, and hybrid COFs) for organic transformations. The catalytic reaction mechanism of COF-based photocatalysts and the influence of dimensionality and crystallinity on heterogenous photocatalysis performance are also discussed, followed by perspectives and prospects on the main challenges and opportunities in future research of COFs and COF-based photocatalyst

Enantioselective inverse-electron demand Aza-Diels-Alder reaction: ipso,α-selectivity of silyl dienol ethers

A highly efficient enantioselective inverse-electron-demand aza-Diels-Alder reaction between aza-sulfonyl-1-aza-1,3-butadienes and silyl (di)enol ethers has been developed. The presented methodology allows the synthesis of benzofuran-fused 2-piperidinol derivatives with three contiguous stereocenters in a highly selective manner, as even the hemiaminal center is completely stereocontrolled. Density functional theory (DFT) calculations support that the hydrogen-bond donor-based bifunctional organocatalyst selectively triggers the reaction through the ipso,α-position of the dienophile, in contrast to the reactivity observed for dienolates in situ generated from β,γ-unsaturated derivatives. Moreover, the calculations have clarified the mechanism of the reaction and the ability of the hydrogen-bond donor core to hydrolyze selectively theEisomer of the dienol ether. Furthermore, to demonstrate the applicability of silyl enol ethers as nucleophiles in the asymmetric synthesis of interesting benzofuran-fused derivatives, the catalytic system has also been implemented for the highly efficient installation of an aromatic ring in the piperidine adductsFinancial support was provided by the European Research Council (ERC-CoG, contract number: 647550), Spanish Government (RTI2018-095038-B-I00), and “Comunidad de Madrid” and European Structural Funds (S2018/NMT-4367

Squaramide-IRMOF-16 analogue for catalysis of solvent-free, epoxide ring-opening tandem and multicomponent reactions

This is the peer reviewed version of the following article: ChemCatChem 10 (2018): 3995-3998, which has been published in final form at http://doi.org/10.1002/cctc.201801127. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsTandem and multicomponent one-pot reactions are highly attractive because they enable synthesis of target molecules in a single reaction vessel. However, they are difficult to control, as they can lead to the formation of many undesired side-products. Herein we report the use of metal-organic framework (MOF) pores decorated with organocatalytic squaramide moieties to confine ring-opening epoxide reactions of diverse substrates. Controlled mono-addition or tandem reactions inside the pores yield 1,2-aminoalcohols or 1,2,2′-aminodialcohols, respectively, in good yields. In addition, this squaramide-functionalised MOF enables catalysis of higher-complexity multicomponent reactions such as the catalytic ring-opening of two different epoxides by a single amine to afford 1,2,2′-aminodialcoholsThis work was supported by the Spanish MINECO (projects PNMAT2015-65354-C2-1-R and CTQ2015-64561-R), the CatalanAGAUR (project 2014 SGR 80), the ERC under the EU FP7 (ERCCo615954 and ERC-CG 647550), and European Union’s Horizon 2020research and innovation programme under grant agreementNo 685727. It was also funded by the CERCA Programme/General-itat de Cataluny

Insulin sensor based on nanoparticle-decorated multiwalled carbon nanotubes modified electrodes

Insulin sensors based on glassy carbon electrodes modified with nafion-multiwalled carbon nanotubes decorated with nickel hydroxide nanoparticles (Ni(OH)<inf>2</inf>NPs/Nafion-MWCNTs/GC), were prepared by electrochemical deposition of Ni(OH)<inf>2</inf>NPs from a dinuclear paddle-wheel Ni monothiocarboxylate complex on the MWCNTs/GC surface. The size and distribution of the Ni(OH)<inf>2</inf>NPs/Nafion-MWCNTs were characterized by transmission electron microscopy (TEM). The results show that Ni(OH)<inf>2</inf> nanoparticles were electrodeposited on the surface of carbon nanotubes. Moreover, the electrochemical behavior of the modified electrodes in aqueous alkaline solutions of insulin was studied by cyclic voltammetry and chronoamperometry. It was found that the as-prepared nanoparticles have excellent electrocatalytic activity towards insulin oxidation due to their special properties, reducing the overpotential and improving the electrochemical behavior, compared to the bare GC electrode. Amperometry was used to evaluate the analytical performance of modified electrode in the determination of insulin. Excellent analytical features, including high sensitivity (5.0 A mol cm<sup>-2</sup> μM<sup>-1</sup>), low detection limit (85 nM) and wide dynamic range (up to 10.00 μM), were achieved under optimum conditions. Moreover, these insulin sensors show good repeatability and a high stability after successive potential cycling. Common substances such as ascorbic acid, uric acid and acetaminophen do not interfere. Finally, the developed sensors have been applied to the determination of insulin in pharmaceuticals and in human plasma. Efficient recoveries for pharmaceuticals and human plasma demonstrate that the proposed methodology can be satisfactorily applied to these types of samplesThe authors acknowledge Ministerio de Economía y Competitividad (project No. CTQ2014-53334-C2-1-R and MAT2013-46753-C2-1-P) and Comunidad de Madrid (NANOAVANSENS Program) for financial support. E.M.P. gratefully acknowledges the FPU-2010 Grant from the Ministerio de Educació

Nanotribology and electrical properties of carbon nanotubes hybridized with covalent organic frameworks

Nanomanipulation of molecular materials such as carbon nanotubes (CNTs) or new covalent organic frameworks (COFs) is key not only for the study of their fundamental physicochemical properties, but also for building and probing nanodevices. Therefore, we have investigated the tribological properties of oxidized MWCNTs (ox-MWCNTs) and their hybridization with COF building blocks (ox-MWCNTs@COF) adsorbed on a mica surface. We used the AFM tip to apply torsional forces on individual nanotubes. Depending on the manipulation parameters, the lateral displacements of the AFM tip slide and/or bend nanotubes enabling the direct quantification of the nanotube-mica adhesion. We found striking changes in the behaviour of the lateral force needed to manipulate each carbon nanotube variant which indicates an increased adhesion of ox-MWCNTs@COF with respect to ox-MWCNTs (∼10x). In addition, the use of the AFM tip as a mobile electrode enabled the measurement of electrical transport through individual nanotubes that revealed a rectifying behaviour of the ox-MWCNTs@COF with high resistivity, which was in contrast with the near ohmic performance of ox-MWCNTsP. J.d.P. acknowledges support by grants from the Ministerio de Ciencia e Innovacion (FIS2017- 89549-R; “Maria de Maeztu” Program for Units of Excellence in R&D MDM2014-0377; and FIS2017-90701- REDT) and the Human Frontiers Science Program (HFSPO RGP0012/ 2018). R. M. ackowledges support by grant PID2019-110637RB-10

Engineering photocatalytic porous organic materials for directing redox versus energy transfer processes

Two organic materials containing phenanthroline and triazine fragments, but connected in different ways, are presented. The imine-based material Phen–Tz–covalent organic framework (COF) preferentially shows photocatalytic activity through an energy transfer pathway as observed for olefin photoisomerization. However, an analogous covalent triazine framework (Phen–CTF) behaves as a powerful photoredox catalyst able to activate C-X (X=Br, Cl) bonds. The analysis of this phenomenon by means of theoretical calculations enables the rationalization of the different photocatalytic behavior observed. Phen–CTF behaves as a donor–acceptor material resulting in efficient charge separation upon excitation, while the imine groups present in Phen–Tz–COF hamper charge separation contributing to the rapid recombination between electrons and holes. This justifies a better activation via electron transfer in Phen–CTF and via energy transfer in Phen–Tz–COFPID2021-122299NB-I0, PID2019-110637RB-I00, ID2020-112715GB-I00, PID2022-141016OB-I00, TED2021-130470B-I0, TED2021-129999B-C32, S2018/NMT-4367, Y2020/NMT64