Rhodium-catalyzed [2+2+2] cycloaddition of 1,6-diynes with isothiocyanates and carbon disulfide

[STRUCTURE: SEE TEXT] A neutral rhodium(I)/BINAP complex effectively catalyzed a [2+2+2] cycloaddition of 1,6-diynes with isothiocyanates to give bicyclic thiopyranimines in 59-98% isolated yield. The reaction with carbon disulfide also proceeded to give bicyclic dithiopyrones in 74-85% isolated yield.     

Ruthenium(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes with tricarbonyl compounds

In the presence of catalytic amounts of Cp*Ru(cod)Cl, unsymmetrical 1,6-diynes possessing a variety of functional groups reacted with electron-deficient tricarbonyl compounds at the ketone C=O double bonds to selectively afford dienones via electrocyclic ring opening of the expected alpha-pyrans. The intramolecular Michael addition of the cycloadducts having an acetyl and an alkylidenemalonate moiety gave bicyclo[3.3.0]octenone derivatives.     

Regioselective intramolecular [3+2] annulation of allene-nitrones

The regioselective intramolecular 1,3-dipolar cycloaddition of the phenylsulfonylallene-nitrone derivatives has been developed. This reaction showed that the distal double bond of the allene exclusively reacted with the nitrone group to produce the bicyclic isoxazolidine derivatives regardless of the substitution pattern on the allenyl moiety.     

Palladium catalysed [2 + 2 + 1] intramolecular cycloaddition for the preparation of bicyclo[3.3.0]octa-1.5-dien-3-ones from 1,6-diynes

Palladium catalysed [2 + 2 + 1] cycloaddition of 1,6-heptadiynes with CO (1 atm) furnishes bicyclo[3.3.0]octa-1,5-dien-3-ones in 30-74% yield.     

Rhodium-catalyzed selective [2+2+2] cyclizations of 1,6-diynes with monoynes leading to isoindolines and isobenzofurans

<正>A highly efficient and selective[2+2+2]cyclization of diynes and monoalkynes was catalyzed by rhodium under room temperature in water/THF mixed solvent,affording isoindolines and isobenzofurans in good to excellent yields.The center atoms (N,O) in the diynes showed a significant effect for the cyclization.     

A [3+2] annulation procedure for methylenecyclopentanes

A two step sequence converts certain cyclic enones to fused methylenecyclopentanes using the annulation reagent 2-chloromethyl-3-trimethylsilylpropene.     

Enantioselective synthesis of axially chiral anilides through rhodium-catalyzed [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides

We have developed a rhodium-catalyzed enantioselective intermolecular [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides for the synthesis of axially chiral anilides. The axial chirality is constructed at the formation of benzene rings with high enantioselectivity (up to 98% ee). It should be noted that the present reaction employs the readily prepared trimethylsilylynamides starting from commercially available bis(trimethysilyl)acetylene and the trimethylsilyl group of the product anilides is expected to be utilized for further functionalization.     

Novel intramolecular [4 + 1] and [4 + 2] annulation reactions employing cascade radical cyclizations

Tributyltin hydride and tris(trimethylsilyl)silane promote sequential/cascade free radical cyclization reactions of dienoate tethered vinyliodides or alkynes. These processes produce [4 + 1] and [4 + 2] annulated products. In contrast, the electrochemical reductions of the vinyliodides afford monocyclic compounds. Both the regiochemical and stereochemical courses of the sequential radical cyclizations strongly depend on substrate structure. Especially important is the balance between steric and stereoelectronic (Baldwin's rules) factors that serve to control cyclization regiochemistry.     

Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates

The efficient phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles with allenoates has been successfully developed, providing a facile access to cyclopenta[b]indolines with good to excellent yields and high diastereoselectivities. This strategy features mild reaction conditions, high functional group tolerance, and scalability. Additionally, the 2-nitrobenzofuran and 2-nitrobenzothiophene were good dearomative [3+2] annulation partners.     

[3+2] Cyclopentane annulation reactions using organoiron reagents. Hydroazulene synthesis.

A one step synthesis of 4-ketohydroazuleneiron complexes 6,7 and 8 from troponeiron tricarbonyl is described.     

An aerobic [2 + 2 + 2] cyclization via chloropalladation: from 1,6-diynes and acrylates to substituted aromatic carbocycles

A Pd-catalyzed aerobic [2 + 2 + 2] cyclization of 1,6-diynes and acrylates proceeding through a chloropalladation process has been developed. Polysubstituted five-membered aromatic carbocycles/heterocycles were obtained in good to excellent yields. The results of the mechanistic study are consistent with the proposed reaction mechanism.     

Catalytic enantiospecific [3+2] annulation of aminocyclopropanes with ketones

An almost familiar ring: The first enantiospecific [3+2] annulation of donor-acceptor aminocyclopropanes with ketones is reported (see scheme; Phth=phthaloyl). The reaction is catalysed by tin(IV) chloride (5?mol?%) at -78?°C and gives aminotetrahydrofurans bearing a quaternary C5 atom in high yield, diastereoselectivity and enantiospecificity (see scheme).     

Phosphine-catalyzed cascade [3 + 2] cyclization-allylic alkylation, [2 + 2 + 1] annulation, and [3 + 2] cyclization reactions between allylic carbonates and enones

The phosphine-catalyzed annulations between Morita-Baylis-Hillman adduct carbonates and enones are reported. Under the catalysis of PBu(3) (20 mol %), cascade [3 + 2] cyclization-allylic alkylation, [2 + 2 + 1] annulation, and [3 + 2] cyclization reactions chemoselectively occur depending on the substituent variation of both the carbonate and enone. These reactions provide efficient syntheses of highly functionalized cyclopentenes and cyclopentanes.     

An unexpected phosphine-catalyzed [3 + 2] annulation. Synthesis of highly functionalized cyclopentenes

An unexpected phosphine-catalyzed [3 + 2] annulation from electron-deficient allenes and substituted alkylidenemalononitriles was realized in which the allylic moiety of the substituted alkylidenemalononitriles served as the three carbon unit of the cyclopentenes instead of the electron-deficient allenes.     

Formal and standard ruthenium-catalyzed [2 + 2 + 2] cycloaddition reaction of 1,6-diynes to alkenes: a mechanistic density functional study

"Formal" and standard Ru(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes 1 to alkenes gave bicyclic 1,3-cyclohexadienes in relatively good yields. The neutral Ru(II) catalyst was formed in situ by mixing equimolecular amounts of [Cp*Ru(CH3CN)3]PF6 and Et4NCl. Two isomeric bicyclic 1,3-cyclohexadienes 3 and 8 were obtained depending on the cyclic or acyclic nature of the alkene partner. Mechanistic studies on the Ru catalytic cycle revealed a clue for this difference: (a) when acyclic alkenes were used, linear coupling of 1,6-diynes with alkenes was observed giving 1,3,5-trienes 6 as the only initial reaction products, which after a thermal disrotatory 6e-pi electrocyclization led to the final 1,3-cyclohexadienes 3 as probed by NMR studies. This cascade process behaved as a formal Ru-catalyzed [2 + 2 + 2] cycloaddition. (b) With cyclic alkenes, the standard Ru-catalyzed [2 + 2 + 2] cycloaddition occurred, giving the bicyclic 1,3-cyclohexadienes 8 as reaction products. A complete catalytic cycle for the formal and standard Ru-catalyzed [2 + 2 + 2] cycloaddition of acetylene and cyclic and acyclic alkenes with the Cp*RuCl fragment has been proposed and discussed based on DFT/B3LYP calculations. The most likely mechanism for these processes would involve the formation of ruthenacycloheptadiene intermediates XXIII or XXVII depending on the alkene nature. From these complexes, two alternatives could be envisioned: (a) a reductive elimination in the case of cyclic alkenes 7 and (b) a beta-elimination followed by reductive elimination to give 1,3,5-hexatrienes 6 in the case of acyclic alkenes. Final 6e-pi electrocyclization of 6 gave 1,3-cyclohexadienes 3.     

Electrocatalytic redox neutral [3 + 2] annulation of N-cyclopropylanilines and alkenes

Although synthetic organic electrochemistry (EC) has advanced significantly, net redox neutral electrosynthesis is quite rare. Two approaches have been employed to achieve this type of electrosynthesis. One relies on turnover of the product by the reactant in a chain mechanism. The other involves both oxidation on the anode and reduction on the cathode in which the radical cation or the radical anion of the product has to migrate between two electrodes. Herein, a home-built electrochemistry/mass spectrometry (EC/MS) platform was used to generate an N-cyclopropylaniline radical cation electrochemically and to monitor its reactivity toward alkenes by mass spectrometry (MS), which led to the discovery of a new redox neutral reaction of intermolecular [3 + 2] annulation of N-cyclopropylanilines and alkenes to provide an aniline-substituted 5-membered carbocycle via direct electrolysis (yield up to 81%). A chain mechanism, involving the regeneration of the substrate radical cation and the formation of the neutral product, is shown to be responsible for promoting such a redox neutral annulation reaction, as supported by experimental evidence of EC/MS.

We report the use of an online electrochemistry/mass spectrometry platform to develop a redox neutral electrosynthesis of 5-membered rings via [3 + 2] annulation of N-cyclopropylanilines and alkenes, without additional oxidant, reductant or catalyst.     

A new strategy for construction of eight-membered carbocycles by Brook rearrangement mediated [6 + 2] annulation

[reaction: see text] A newly developed strategy for construction of eight-membered carbocycles via [6 + 2] annulation that involves the combination of beta-alkenoyl acylsilanes and a vinyllithium derivative is described. A unique feature of this annulative approach is that it enables in one operation and a stereoselective manner construction of eight-membered ring systems containing useful functionalities for further synthetic elaboration from readily available six- and two-carbon components.     

Density functional theory study of ruthenium (II)-catalyzed [2+2+2] cycloaddition of 1,6-diynes with tricarbonyl compounds

Density functional theory has been employed to study the mechanism of the [2+2+2] ruthenium(II)-catalyzed cycloaddition between 1,6-diynes and tricarbonyl compounds, proposing a viable multistep-pathway according with that was previously suggested, but clarifying some aspects. This process is compared with the one-step reaction in absence of catalyst.