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The synthesis of spiro compounds featuring seven- and six-membered rings in the spirobicyclic motif is successfully achieved through a cascade process encompassing a rhodium(I)-catalyzed cycloisomerization followed by a highly selective Diels-Alder homodimerization. The scope of the reaction is analyzed based on a series of synthetic substrates, and control experiments and DFT calculations led us to justify the exquisite degree of selectivity observed We are grateful for financial support from the Ministerio de Ciencia e Innovación (PID2020-113711GB-I00 MCIN/AEI/ 10.13039/501100011033), the Generalitat de Catalunya (Project 2017-SGR-39), and the UdG for an IF predoctoral grant to J.V. Open Access funding provided thanks to the CRUE-CSIC agreement with ACS

The mechanism for the functionalizaton of 2-alkylpyridine and 2-alkylquinoline derivatives by nitrogen transfer from N2O is unveiled. The reaction is predicted to be feasible for other derivatives featuring N−, O−, and S− heterocycles.

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.

A synthetic methodology is reported that functionalizes C60 and C70 fullerenes with dihydroazepine rings by a cascade reaction encompassing a rhodium-catalyzed cycloisomerization of 1,5-bisallenes and a [4+2] cycloaddition. This transition metal-catalyzed cascade reaction provides a versatile and step-economical approach to the synthesis of 6,7-membered polyheterocyclic fullerene adducts. Electrochemical characterization of the products obtained ventures their application in organic and perovskite photovoltaic devices We are grateful for the financial support by the Spanish Ministry of Economy and Competitivity (MINECO) (Projects CTQ2017-85341-P and CTQ2017-83587-P, FPI predoctoral grant to A.A. and C.C.) and the Generalitat de Catalunya (Project 2017-SGR-3 Open Access funding provided thanks to the CRUE-CSIC agreement with Wiley

The development of catalytic methodologies involving the formation of C−C bonds to enable the generation of cyclic systems constitutes a field of great relevance in synthetic organic chemistry. One paradigmatic process to accomplish this goal efficiently is the transition-metal-catalyzed [2 + 2 + 2] cycloaddition reaction, since it permits the formation of a wide range of highly functionalized 6-membered carbo- and heterocyclic molecules in a single step with high efficiency and perfect atom economy. A key feature of these transformations is the mechanistic pathway that they follow, since a deep knowledge of this mechanism may enable us to understand and improve the efficiency of the reaction. This review covers the mechanistic aspects, studied both from theoretical and experimental points of view, of the transition-metal-catalyzed [2 + 2 + 2] cycloaddition reaction involving all kinds of unsaturated substrates with metals such as Co, Ni, Ru, Rh, Ir, Pd, Zr, Ti, Ta, and Nb. A thorough overview is undertaken, from the seminal studies until the present day, of the key mechanistic aspects that influence the reactivity and selectivity of the reaction, comparing the involvement of different unsaturated substrates as well as the different transition metals used We gratefully acknowledge the financial support of our own research in this area by the Spanish Ministry of Economy and Competitivity (MINECO) (project CTQ2017-85341-P) and the Generalitat de Catalunya (project 2017-SGR-39, Xarxa de referencia en Química Teórica i Computacional, and ICREA Academia 2014 Award to M.S.)

[2+2+2] Cycloaddition reaction is a captivating process that assembles six-membered rings from three unsaturations with complete atom economy. Of the multiple transition metals that can be used to catalyze this reaction, rhodium offers many advantages. These include high activity and versatility, but especially the ability to easily tune the reactivity and selectivity by the modification of the ligands around the metal. In this personal account, we summarize our endeavours in the development of efficient and sustainable [2+2+2] cycloaddition reactions to prepare products of interest, develop conditions in which the catalyst can be recovered and reused, and understand the mechanistic details that govern the selectivity of the processes This research was funded by the Ministerio de Ciencia e Innovación (projects CTQ2017-85341-P, PID2020-113711GB-I00 MCIN/AEI/10.13039/501100011033) and the Generalitat de Catalunya (Project 2017-SGR-39)

Density functional theory calculations were used to systematically explore the effects of axial ligation by solvent molecules on the reactivity and selectivity of dirhodium tetracarboxylates with diazo compounds in the context of C–H insertion into propane. Insertions on three types of diazo compounds—acceptor/acceptor, donor/acceptor, and donor/donor—promoted by dirhodium tetraformate were tested with and without axial solvent ligation for no surrounding solvent, dichloromethane, isopropanol, and acetonitrile. Magnitudes, origins, and consequences of structural and electronic changes arising from axial ligation were characterized. The results suggest that axial ligation affects barriers for N2 extrusion and C–H insertion, the former to a larger extent.

Density functional theory calculations were used to systematically explore the effects of axial ligation by solvent molecules on the reactivity and selectivity of dirhodium tetracarboxylates with diazo compounds in the context of C–H insertion into propane. Insertions on three types of diazo compounds—acceptor/acceptor, donor/acceptor, and donor/donor—promoted by dirhodium tetraformate were tested with and without axial solvent ligation for no surrounding solvent, dichloromethane, isopropanol, and acetonitrile. Magnitudes, origins, and consequences of structural and electronic changes arising from axial ligation were characterized. The results suggest that axial ligation affects barriers for N2 extrusion and C–H insertion, the former to a larger extent.