Dimensioning the term carbenoid

The current use of the term carbenoid is discussed, particularly in the context of carbene transfer reactions from diazo compounds, where intermediates of type LnM=CR1R2, or one of its resonance forms, are tagged which such name. We herein discuss this issue, on the basis of the data evidencing the metal-carbene nature of those intermediates, as well as the existence of carbenoids of type (N2)(M)C R1R2 en route to the formation to LnM=C R1R2’ from diazo reagents. We propose the exclusive use of the carbenoid term to species of type (X)(M)C R1R2 with a tetrasubstituted carbon center that upon loss of X afford an effective carbene transfer process.The authors wish to thank MINECO for financial support (CTQ2014-52769-C03-01) and Junta de Andalucia (P12-FQM-1765)

Alkenylboronates : synthesis and applications

Organoboron compounds have become one of the most versatile building blocks in organic synthesis owing to their accessible and efficient conversion into many different functional groups. In particular, alkenyl boronates have received a great deal of attention as very reactive substrates in Suzuki–Miyaura cross‐coupling reactions. Accordingly, efforts towards the development of efficient methods to prepare this type of compound are ongoing. In this contribution, the progress in the search for synthetic routes for alkenyl boronates and their use in a variety of organic transformations is accounted.The authors wish to thank MINECO for financial support (CTQ2017-82893-C2-1-R and Juan de la Cierva fellow for J.C.) and Junta de Andalucía (P12-FQM-1765)

Make It Green: Copper-Catalyzed Olefin Aziridination in Water with an Iminoiodonane

The copper complex Tp(CF3)2,BrCu(NCMe) efficiently catalyses the aziridination of olefins in water using PhI=NTs as the nitrene source, with identical activity than that observed when using dichloromethane as the solvent, under the same experimental conditions. No specific modification of catalyst or substrates are required, nor the presence of additional phase transfer catalyst. Competition experiments and Hammett plots show that the behaviour of the metal centre is the same in both reaction media. This is the first example of a catalytic system employing PhI=NTs for olefin aziridination in water.We thank financial support from the Ministerio de Ciencia e Innovación (PID2020-113797RB-C21), Junta de Andalucía (P18- RT-1536) and Universidad de Huelva (P.O.Feder UHU-1260216). Funding for open access charges is given by Universidad de Huelva/CBUA

Measuring the Relative Reactivity of the Carbon-Hydrogen Bonds of Alkanes as Nucleophiles

We report quantitative measurements of the relative reactivities of a series of C-H bonds of gaseous or liquid CnH2n+2 alkanes (n = 1-8, 29 different C-H bonds) towards insitu generated electrophiles (copper, silver, and rhodium carbenes), with methane as the reference. This strategy surpasses the drawback of previous model reactions of alkanes with strong electrophiles suffering from C-C cleavage processes, which precluded direct comparison of the relative reactivities of alkane C-H bonds.We thank MINECO for support with Grants CTQ2014-52769-C03-01, CTQ2014-52769-C03-02, CTQ2017-82893-C2-1-R, CTQ2014-62234-EXP, CTQ2015-73693-JIN, CTQ2017-87792-R, Severo Ochoa Excellence Accreditation 2014-2018 (SEV-2013-0319), and Red Intecat (CTQ2016-81923-REDC). Junta de Andalucia is also acknowledged for Grant P12-FQM-1765. R.G. and A.O. thank MINECO for FPI and Juan delaCierva fellowships, respectively. B.N. thanks MEC for a FPU fellowship. The CNRS is thanked for support

Catalytic Functionalization of C-H Bonds of Azulene by Carbene/Nitrene Incorporation

The selective catalytic functionalization of the C-H bond of azulene upon incorporation of carbene or nitrene units with metal-based catalysts is described. Ethyl diazoacetate or ArI=NTs are employed as carbene or nitrene precursors, respectively. The azulene derivatives are subsequently employed as building blocks toward more complex structures with potential use as biodegradable materials.We thank MINECO (CTQ2017-82893-C2-1-R and Juan de la Cierva fellowship for J.C.), Junta de Andalucia for Grant P12-FQM-1765, and CHAOS COST ACTION CA-15106. We also thank Manuel A. Pulido for preliminary experiments and Francisco Molina for X-ray structure determination

A Quantitative Model for Alkane Nucleophilicity Based on C−H Bond Structural/Topological Descriptors

A first quantitative model for calculating the nucleophilicity of alkanes is described. A statistical treatment was applied to the analysis of the reactivity of 29 different alkane C−H bonds towards in situ generated metal carbene electrophiles. The correlation of the recently reported experimental reactivity with two different sets of descriptors comprising a total of 86 parameters was studied, resulting in the quantitative descriptor‐based alkane nucleophilicity (QDEAN) model. This model consists of an equation with only six structural/topological descriptors, and reproduces the relative reactivity of the alkane C−H bonds. This reactivity can be calculated from parameters emerging from the schematic drawing of the alkane and a simple set of sums.We thank MINECO for support with Grants CTQ2017-82893-C2- 1-R, CTQ2015-73693-JIN, CTQ2017-87792-R and Red Intecat (CTQ2016-81923-REDC). Junta de Andalucía is also acknowledged for Grant P12-FQM-1765. R. G. and A. O. thank MINECO for FPI and Juan de la Cierva fellowships, respectively

Favoring alkane primary carbon-hydrogen bond functionalization in supercritical carbon dioxide as reaction medium

The selectivity of a catalytic alkane functionalization process can be modified just changing the reaction medium from neat alkane to supercritical carbon dioxide (scCO2). A silica supported copper complex bearing an Nheterocyclic carbene ligand promotes the functionalization of carbon-hydrogen bonds of alkanes by transferring the CHCO2Et group from N2=CHCO2Et (ethyl diazoacetate, EDA). In neat hexane only 3% of the primary C-H bonds (ethyl heptanoate being the product) are functionalized in that manner, whereas the same reaction carried out in scCO2 provides a 30% yield in this linear ester. Such effect seems to be induced by an electronic density flux from the NHC ligand to the surrounding carbon dioxide molecules.We thank MINECO (CTQ2017-82893-C2-1-R, CTQ2014- 52769-C3-R-2 and CTQ2014-57761-R) and Junta de Andalucía for Grant P12-FQM-1765. J.T.S. thanks MINECO for a FPI fellowship. We acknowledge the SCSIE (Universidad de Valencia) for access to instrumental facilities. We thank Prof. Jesús de la Rosa (Centro de Investigación en Química Sostenible, Universidad de Huelva, Spain) for ICP-MS data

Copper-Catalyzed Dehydrogenative Amidation of Light Alkanes

The functionalization of C-H bonds in light alkanes, particularly to form C-N bonds, remains a challenge. We report the dehydrogenative coupling of amides with C1–C4 hydrocarbons to form N-alkyl amide products with tBuOOtBu as oxidant, and a copper complex of a phenanthroline-type ligand as catalyst. The reactions occurred in good yields in benzene or supercritical carbon dioxide as solvents. This strategy allowed for the determination of the relative reactivity of these alkane C-H bonds toward this amination process and showed, in contrast to prior work with larger alkanes, that the reactivity correlated with bond dissociation energies.Support for this work was provided by the MINECO (CTQ2017-82893-C2-1-R), Junta de Andalucía (P18-RT-1536) and PO FEDER 2014–2020 (UHU-1260216). Work at UCB was supported by the Director, Office of Science, of the US Department of Energy under contract no. DE-AC02- 05CH11231. M.A.F. thanks MINECO for a Juan de la Cierva Incorporación fellowship. Funding for open access charges is given by Universidad de Huelva/ CBUA

Intramolecular Interception of the Remote Position of Vinylcarbene Silver Complex Intermediates by C(sp3)−H Bond Insertion

The trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp3)−H bond has been achieved for the first time during a silver-catalyzed carbene/alkyne metathesis (CAM) process. A Tpx-containing silver complex first promotes the generation of a donor-acceptor silver carbene which triggers CAM, generating a subsequent donor-donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp3)−H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C−H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step.We are grateful for financial support from the Ministerio de Ciencia e Innovación (PGC2018-097722-B-I00, PID2020113797RB-C21 and PID2020-113711GB-I00 MCIN/AEI/ 10.13039/501100011033 and FPU grants to A.D.-J. and R.M.-C.) and the Generalitat de Catalunya (Project 2017SGR-39). We also thank Junta de Andalucía (P18-1536) and Universidad de Huelva (P.O.Feder UHU202024). A.P.Q. and A.P. are Serra Húnter Fellows and A.P. thanks ICREA Academia Prize 2019. M.A. thanks Junta de Andalucia for a postdoctoral fellowship. E.B. thanks Cátedra Cepsa-Universidad de Huelva for financial support