Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitization of allenamides. The visible-light-promoted process gives complex [2.2.2]-(hetero)-bicyclooctadienes at room temperature, likely through the stabilization of transient (bi)radicals by naphthalene. The reaction tolerates several valuable functionalities, offering a convenient handle for a myriad of applications, including original isoindoles and metal complexes.

Aromatic triangular tri-palladium cations 1-3, abbreviated as [Pd-3](+), have shown interesting photoelectric properties, Lewis basic character, and excellent activities in catalytic hydrogenation. Herein, we report the highly efficient and C-I selective Sonogashira and Heck coupling reactions catalyzed by these tri-palladium complexes. Benefiting from the moderate C-I bond association energy, these tri-palladiums presented exclusive reactivities to aryl iodides over the brominated aromatics in coupling reactions. In the Sonogashira pathway, good to excellent isolated yields (71-95%) were achieved. Gram-scale reaction reached 93% of yield with palladium loading as few as 0.06 mol%. We also explored the electronic and steric effects for phenyl alkynes and aryl iodides including heteroaromatics like thiophene, pyridine, pyrazole, and pyrazine. Similarly, yields of 71-96% were obtained for palladium loading of 1.5 mol% through catalyzed Heck coupling of aryl iodides and alkenes. The HRMS monitoring revealed that [Pd-3](+) maintained as whole entity during the catalytic process due to its robusness.

The visible-light-promoted activation of conjugated C-C double bonds is well developed, while that of cumulated systems is underexplored. We present the feasibility of this challenging approach. The localization of a triplet on an allenamide arm can be favored over that on a conjugated alkene. Allenamides with an arylacryloyl arm dimerize at room temperature in the presence of visible light and an iridium(iii) photocatalyst. Two orthogonal polycyclizations took place and their outcome is entirely dictated by the substitution of the alkene partner. Both cascades afford complex molecular architectures with high selectivity. Products form through the ordered rearrangement of twelve π electrons, providing a [3.2.0] bicyclic unit tethered to a fused tricycle, whose formation included an aryl C-H functionalization step, using disubstituted alkenes. The outcome was reverted with trisubstituted ones, which gave rise to taxane-like bridged tricycles that had two six-membered lactams flanking a cyclooctane ring, which was established through the creation of four alternate C-C bonds.

This manuscript describes an overview on the literature detailing the observation of trinuclear complexes that present delocalized metal-metal bonds similar to those of regular aromatics, which are formed combining main group elements. A particular emphasis is given to the structural and electronic features of aromatic clusters that are sufficiently stable to allow their isolation. In parallel to the description of their key bonding properties, the work presents reported catalytic applications of these complexes, which already span from elaborated C-C-forming cascades to highly efficient cross-coupling methods. These examples present peculiar aspects of the unique reactivity exerted by all-metal aromatic complexes, which can often be superior to their established, popular mononuclear peers in terms of chemoselectivity and chemical robustness.

The work details a mechanistic study based on density functional theory modeling on the cycloisomerization of polyunsaturated substrates catalyzed by all-metal aromatic tripalladium complexes and carboxylic acids. These clusters are an emerging class of catalysts for a variety of relevant transformations, including C-C forming processes that occur under mild conditions and display synthetic features complementary to those of established mononuclear complexes. This study is the first computational one devoted to the comprehension of the series of elementary steps involved in a synthetic transformation catalyzed by an all-metal aromatic complex. Present results confirm previous experimental hints on the striking mechanistic differences exerted by these clusters with respect to the usual cyclization pathways of related substrates. Moreover, the catalytic cycle involving present all-metal aromatic clusters closely parallels the mechanism of the aromatic substitution of regular arenes.

Enallenes can be readily converted into two families of 3.2.0 (hetero)bicycles with high diastereoselectivities through the combination of visible light with a suitable Ir(III) complex (1 mol %). Two complementary pathways, namely, a photocycloaddition versus a radical chain, can then take place. Both manifolds grant complete regiocontrol of the allene difunctionalization. This is accompanied by an original 1,3-group shift using sulfonyl allenamides that deliver a congested tetrasubstituted headbridging carbon in the corresponding product.

Très utiles pour une synthèse orientée vers la diversité moléculaire, les réactions multicomposants offrent un accès rapide à une grande variété de molécules complexes, d’intérêt biologique notamment.Cet ouvrage analyse ces réactions, qu’elles soient réalisées en catalyse organométallique, par voie ionique ou en condition radicalaire. Il met en exergue le grand intérêt des méthodes basées sur les réactions monotopes (cascades, tandems ou domino), dont l’efficacité est illustrée aussi bien dans le domaine académique qu’industriel. Il présente également la préparation efficace de molécules complexes d’utilité biologique.Les réactions multicomposants sont donc en phase avec le concept d’économie d’atomes et celui d’économie d’étapes, désormais clés dans tout processus, allant de l’échelle du laboratoire à celle du pilote. Les critères essentiels de la Green Chemistry sont ainsi remplis.

The distinct reactivity of 1,6-enynes in the presence of a trinuclear metal complex activated by a carboxylic acid is presented. The triplatinum catalyst enables the cyclization of the substrate and subsequent incorporation of a nucleophile in the final product. In contrast, sequential cyclization/double bond shift occurs under analogous conditions in the presence of the corresponding tripalladium complex.

Steering the regiochemical outcome with a cationic gold–phosphite catalyst.

Méthodes d’activation en sonochimie traite des améliorations récentes en sonochimie et dans les réactions hyperbare.La sonochimie, une méthode simple à utiliser, permet d’effectuer des réactions chimiques sous ultrasons sans apport extérieur de chaleur, de réactifs, de catalyseurs. Elle conduit à des rendements élevés et à la production d’un minimum de déchets. L’ouvrage fait un tour d’horizon des principales applications de la sonochimie en chimie organique verte, se concentrant tout particulièrement sur les travaux publiés ces dernières années.La chimie sous haute pression, quant à elle, offre des solutions innovantes aux problèmes de synthèse et donne accès à de nouveaux produits ou à l’élucidation des mécanismes réactionnels. L’ouvrage présente les caractéristiques de l’activation hyperbare, qui permettent de l’intégrer à l’arsenal des outils de la chimie verte, telles que la diminution du coût énergétique et des sous-produits, ou la possibilité d’utilisation des substrats stériquement encombrés généralement inertes.

A variety of linear dienynes can deliver complex tetracyclic frameworks in the presence of an IrIII complex and visible light. Product formation involves the generation of four new C-C bonds and six contiguous stereocenters, which decorate two [3.1.0] bicyclic units tethered through their bridging quaternary carbon atoms. The internal alkyne acts as a formal dicarbenoid for the generation of two cyclopropanes in these radical cation cascades. This behavior has not been previously observed for organic reactive intermediates and can be extended to intermolecular reactions and diendiynes.

The combination of a Pd(0) complex with benzoic acid converts propargylic tryptamines to the corresponding tetrahydro-β-carbolines. The method uses unprotected indoles and affords the desired products with ample functional group tolerance. Detailed modeling studies reveal a close synergy between the organic and metal catalysts, which enables sequential alkyne isomerization, indole C-H activation, and eventual C-C reductive elimination to afford the target heterocycles.

An in situ formed palladium hydride catalyst enables the sequential dual isomerization of propargylamide derivatives to 1-amido-1,3-dienes with high chemo- and regioselectivity. The reaction shows ample functional group tolerance, delivering a valuable class of products, including highly deuterated ones, from readily available reagents. The reaction occurs through a complex mechanism studied by DFT modelling.

Highly symmetric all-metal aromatic Pd3+ complexes can catalyze the cycloisomerization of terminal 1,6-enynes and internal dienynes under mild conditions. Modification of substrates dictates the mechanism and steers the reaction toward different polycyclic frameworks, enabling the development of complex cascades. The reactivity of Pd(4/3) complexes is complementary to that of mononuclear Pd(0) and Pd(II) ones.

Arylhydroxylamines were used in the nitroso‐Diels–Alder reaction to generate in situ nitrosoarenes under visible‐light, catalytic and aerobic conditions. Mixing a solution of aryl‐ or heteroarylhydroxylamines with conjuguated dienes in the presence of a catalytic amount of Ru(bpy) 3 Cl 2 afforded 3,6‐dihydro‐1,2‐oxazines in good yields under an oxygen atmosphere.

The cover picture shows the nitroso-Diels–Alder reaction between hydroxylamines and conjugated dienes. This tandem process is achieved by an in situ aerobic oxidation. In fact, the Ru2+ photocatalyst can selectively oxidize hydroxylamines to nitroso intermediates, allowing the one-pot synthesis of the desired 3,6-dihydro-1,2-oxazines. These oxidizing conditions show a broad functional-group tolerance towards both reaction partners, validating the synthetic potential of the method. Details are discussed in the Communication by G. Masson et al. on page 2095 ff (DOI: 10.1002/ejoc.201601492).

Suitably delocalized metal metal bonds can stabilize a particular class of discrete trinuclear complexes that are the transition-metal counterparts of carbon-based aromatics. This chemical stability has pivoted the development of an advantageous catalytic method for the semireduction of internal alkynes under transfer hydrogenation condition. The reaction does not require any additional solvent and a simple workup delivers pure products. This combines with broad functional group tolerance, complete cis-selectivity and catalytic charges down to 100 ppm on multigram scale.

Highly functionalized heterocyclic compounds were synthesized by palladium and norbornene catalysis starting from ortho-substituted aryl iodides, aryl bromides and 3,4-ethylenedioxythiophene. The addition of methyl cinnamate to the reaction mixture was found to be crucial in order to obtain selectively the unsymmetrical product.