RESUMEN

A remarkable stereodivergent cyclotrimerization of 9,10-didehydrotribenzo[8]annulene (tribenzoCOTyne) to the corresponding (α,α,α)- and (α,α,ß)-benzofused derivatives has been developed by controlling the reaction conditions. While the K+-mediated cyclotrimerization afforded the (α,α,α) stereoisomer, using Pd as a catalyst resulted in the (α,α,ß)-derivative. Both stereoisomers were evidenced by spectroscopic data and crystal X-Ray analysis. The (α,α,α) stereoisomer is a fragment of cubic graphite (CG), an elusive 3D carbon allotrope that contains carbon cages, since all of its sixty carbons are part of the structure of CG, and 36 constitute a part of the C48 molecular cage of CG. Experimental and computational mechanistic studies revealed that the potassium ion would play a key role as a template to favor the formation of the (α,α,α) stereoisomer.

RESUMEN

The first Pd-catalyzed [5 + 2] rollover annulation of 1-benzylpyrazoles with alkynes to assemble 10H-benzo[e]pyrazolo[1,5-a]azepines (tricyclic 2-benzazepines) has been developed. The rollover annulation implies a twofold C-H activation of aryl and heteroaryl Csp2-H bonds (C-H/C-H) of 1-benzylpyrazoles (five-atom partners) and alkynes to give the [5 + 2] annulated compounds.

RESUMEN

The Ru-catalyzed intramolecular oxidative amidation (lactamization) of aromatic alkynylamines with 4-picoline N-oxide as an external oxidant has been developed. This chemoselective process is very efficient to achieve medium-sized ε- and ζ-lactams (seven- and eight-membered rings) but not for the formation of common δ-lactams (six-membered rings). DFT studies unveiled the capital role of the chain length between the amine and the alkyne functionalities: the longer the connector, the more favored the lactamization process vs hydroamination.

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RESUMEN

Functionalized alicyclic amines are important building blocks for the synthesis of bioactive natural compounds and drugs. Existing methods of functionalization are typically limited to the synthesis of protected amines or the use of highly basic organometallic reagents that can compromise functional group tolerance. Here, we report a novel approach that enables the transformation of O-benzoyl hydroxylamines into α-functionalized cyclic secondary amines by means of a copper-catalyzed regio-, stereo-, and chemoselective coupling with allenes and bis(pinacolato)diboron. A key feature of the present transformation is the use of a catalytic Lewis base additive which inhibits the competing C-N bond forming reaction between the catalytically generated boron-substituted allylcopper intermediate with the O-benzoyl hydroxylamine, thus enabling in situ transformation of the latter into an alicyclic imine which undergoes selective C-C bond formation with the allylcopper species.

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RESUMEN

Pd-catalyzed allylic C-H activation of simple olefins allows an easy entry to seven-membered N,O-heterocycles such as 1,4-benzoxazepines (1,4-BZOs), 1,4-benzodiazepinones (1,4-BZDs) and 1,4-oxazepanes in good to excellent yields. Straightforward derivatization of the olefinated 1,4-BZO shows the synthetic utility of this methodology.

RESUMEN

Benzofused seven-membered heterocycles such as 1,4-benzo[e]diazepines (1,4-BZDs) and 1,4-benzo[e]oxazepines (1,4-BZOs) were efficiently synthesized by Rh-catalyzed hydrofunctionalization of internal alkynes and allenes in good to excellent yields. The asymmetric hydroamination of (aminomethyl)anilines gave rise to 3-vinyl-1,4-BZDs with excellent enantioselectivities. Orthogonal N-deprotection of 1,4-BZDs allowed an easy entry to an advanced pyrrolobenzodiazepine metabolite of the V2-receptor antagonist Lixivaptan.

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RESUMEN

A novel tandem Ru-catalyzed [2+2+2] cycloaddition of arylenynes to dihydrobiphenylenes followed by halogen-radical ring opening has been developed for the construction of tub-shaped halogenated benzocyclooctatetraenes (bCOT's). Cross-couplings and Diels-Alder reactions of the brominated bCOT's allow the formation of the corresponding eight-membered ring-fused PAH's. The halogen-radical ring opening probably occurs via a selective formation of a bis-allyl radical at the 1,3-cyclohexadiene moiety, halogenation at the bridgehead carbon, and finally electrocyclic ring opening.

RESUMEN

Phenethyltriflamides react with 1,3-dienes upon treatment with a catalytic amount of Pd(OAc)2 and Cu(OAc)2/O2 as oxidant to afford chemo-, regio- and diastereoselectively 2,3,4,5-tetrahydro-1H-benzo[d]azepines (3-benzazepine derivatives) in good to excellent yields. A DFT study of the [5 + 2] heteroannulation suggests a mechanistic pathway starting with formation of the six-membered palladacycle cis-PdX2L2 via a CMD process followed by η2 coordination and insertion of the 1,3-diene unit in a diastereoselective manner.

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RESUMEN

Ruthenium vinyl carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-vinyl dihydrooxazines are preferentially obtained with the former, Z-vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3 -coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.

RESUMEN

The Cp*RuCl-based catalyst enables expedient access to a variety of benzofused six-membered azaheterocycles from unprotected o-alkynylanilines and trimethylsilyldiazomethane through an unprecedent tandem carbene/alkyne metathesis/N-H insertion reaction. The transformation takes place under mild reaction conditions (room temperature, <15 min) and with excellent functional group tolerance. The synthetic utility of the final products and a mechanistic rationale are also discussed.

RESUMEN

Complex CpRuCl(PPh3)2 catalyzes reactions of terminal alkynes with 4-picoline N-oxide and primary and secondary amines to afford the corresponding amides. The reactions occur in chlorinated solvent and aqueous medium, showing applications in peptide chemistry. Stoichiometric studies reveal that the true catalysts of the processes are the vinylidene cations [CpRu(═C═CHR)(PPh3)2]+ which are oxidized to the Ru(η2-CO)-ketenes by the N-oxide. Finally, nucleophilic additions of primary and secondary amines to the free ketenes yield the corresponding amides.

RESUMEN

A novel and mild Rh(III)-catalyzed [5 + 2] oxidative annulation between cyclic arylguanidines and alkynes efficiently affords 1,3-benzodiazepines (pentacyclic guanidines). The use of O2 as the sole oxidant in place of commonly used metal oxidants such as AgOAc clearly improves the efficiency of the oxidative annulation process. The mechanism of the cycloaddition most likely involves the formation of an eight-membered rhodacycle. DFT calculations support a striking mechanistic proposal for the [5 + 2] oxidative annulation.

RESUMEN

A novel class of N-doped cationic PAHs (polycyclic aromatic hydrocarbons) bearing the benzo[c,d]fluoranthene scaffold has been synthesized by the Rh(III)-catalyzed double-oxidative annulation of 2-arylbenzimidazoles with alkynes. The overall process involves a double C-N bond formation through a double C-H/N-H functionalization.The solid-state structures and electronic properties of the new N-doped PAHs were analyzed. These cationic azapolycycles were readily reduced in the presence of LiAlH4 or by the addition of PhLi to give interesting phenyl and diphenylmethanediamine derivatives.

RESUMEN

Recent developments in catalytic carbonyl-olefin metathesis are summarized in this Highlight. Schindler and co-workers have reported that the environmentally benign FeCl3 catalyst promotes ring-closing carbonyl-olefin metathesis (RCCOM) in high yield under very mild conditions.

RESUMEN

A novel route to 1,3-oxazaheterocycles based on cooperative Ru-H/Brønsted acid catalysis is reported. The use of the commercially available RuH2(CO)(PPh3)3 complex allows for an efficient long distance chain-walking process while the Brønsted acid is responsible for generation of an electrophilic iminium ion which is trapped intramolecularly by an alcohol moiety. The alcohol, besides its nucleophilic function, also plays an important role in the stabilization of the Ru catalyst.

RESUMEN

A novel osmium-catalyzed cyclization of o-alkynyl phenethylamines to give 3-benzazepines is reported. The procedure allows the straightforward preparation of a broad range of dopaminergic 3-benzazepine derivatives. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, which were isolated and characterized by X-ray crystallography.

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RESUMEN

A novel and mild Rh(III)-catalyzed [5+1] oxidative cycloaddition between arylguanidines and alkynes efficiently affords C4-disubstituted 1,4-dihydroquinazolin-2-amines. Members of this family of heterocycles, which contain the relevant cyclic guanidine units, have shown interesting pharmacological properties. The mechanism probably involves the formation of an eight-membered rhodacycle in which the imine unit of guanidine is coordinated to the Rh center. This rhodacycle would evolve to give the C-4 disubstituted 1,4-dihydroquinazolin-2-amine skeleton.

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RESUMEN

A new ruthenium-catalyzed cyclization of ortho-(alkynyloxy)benzylamines to dihydro-1,3-benzoxazines is reported. The cyclization is thought to take place via the vinyl ruthenium carbene intermediates which are easily formed from [Cp*RuCl(cod)] and N2 CHSiMe3 . The mild reaction conditions and the efficiency of the procedure allow the easy preparation of a broad range of new 2-vinyl-2-substituted 1,3-benzoxazine derivatives. Rearrangement of an internal C(sp) in the starting material into a tetrasubstituted C(sp(3) ) atom in the final 1,3-benzoxazine is highly remarkable.

RESUMEN

A novel synthesis of 2-vinyldihydropyrans and dihydro-1,4-oxazines (morpholine derivatives) from alkynals and alkynones has been developed. The cyclizations require a mild generation of catalytic ruthenium carbenes from terminal alkynes and (trimethylsilyl)diazomethane followed by trapping with carbonyl nucleophiles. Mechanistic aspects of the new cyclizations are discussed.

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RESUMEN

A new synthetic route to dihydrobiphenylenes has been developed. The process involves a mild Ru(II) -catalyzed [2+2+2] dimerization of ortho-alkenylarylacetylenes or its more versatile variant, the Ru-catalyzed [2+2+2] cycloaddition of ortho-ethynylstyrenes with alkynes. Mechanistic aspects of this [2+2+2] cycloaddition are discussed.