Iridium-catalyzed [2+2+2] cycloaddition of α,ω-diynes with isocyanates

[Ir(cod)Cl](2)/BINAP was found to be an efficient catalyst for the [2+2+2] cycloaddition of α,ω-diynes with isocyanates to give 2-pyridones. A wide range of isocyanates can be used for this reaction. Both aliphatic and aromatic isocyanates smoothly reacted with α,ω-diynes to give 2-pyridones in high yields. Aliphatic isocyanates were more reactive than aromatic isocyanates. For aromatic isocyanates, the electronic properties of the substituents affected the reactivity: electron-donating substituents enhanced the reaction. The reaction of unsymmetrical α,ω-diynes possessing two different internal alkyne moieties with isocyanates was regiospecific and gave a single product. This regioselectivity could be explained by the reaction of iridacyclopentadiene with a nitrogen-carbon double bond. The regioselectivity of the reaction of malonate-derived diyne was controlled by a steric effect, while that of the reaction of ester-tethered diyne was controlled by an electronic effect. [Ir(cod)Cl](2)/chiral diphosphine catalyst could be used for the enantioselective synthesis of C-N axially chiral 2-pyridone. The reaction of diyne 1a with o-methoxyphenyl isocyanate (7a) gave C-N axially chiral 2-pyridone (R)-8aa in 78% yield with 94% ee.     

Iridium-catalyzed [2+2+2] cycloaddition of α,ω-diynes with alkynyl ketones and alkynyl esters

We found that the combination of [Ir(cod)Cl]₂ and rac-BINAP served as an efficient catalyst for the [2+2+2] cycloaddition of 2,7-nonadiyne derivatives and related compounds with alkynyl ketones and alkynyl esters. The corresponding products were obtained in high yields under mild reaction conditions.     

Rhodium(I)/cationic 2,2′-bipyridyl-catalyzed [2+2+2] cycloaddition of α,ω-diynes with alkynes in water under air

A simply performed procedure for the [Rh(cod)Cl]₂/cationic 2,2′-bipyridyl system-catalyzed [2+2+2] cycloaddition of α,ω-diynes with terminal and internal alkynes was achieved in water under air at 60 °C. The reaction proceeded smoothly with 1 equiv α,ω-diynes and 3 equiv alkynes in the presence of 20 mol % KOH for 1 h or 9 h, resulting in the formation of tri- and tetra-substituted benzene derivatives in moderate to high yields. After separation of the organic products by extraction, the residual aqueous solution could be reused for further reactions until complete degradation of its catalytic activity.     

Enantioselective synthesis of α,α-disubstituted α-amino acids by Rh-catalyzed [2+2+2] cycloaddition of 1,6-diynes with protected dehydroamino acid

We have determined that a cationic rhodium(I)/BINAP complex catalyzes a [2+2+2] cycloaddition of 1,6-diynes with a protected dehydroamino acid, leading to protected α-amino acids bearing a quaternary carbon center in high yield with high enantioselectivity.     

Brønsted acid TfOH-mediated [3 + 2] cycloaddition reactions of diarylvinylidenecyclopropanes with nitriles

Diarylvinylidenecyclopropanes undergo a [3 + 2] cycloaddition reaction with MeCN in the presence of Br?nsted acid TfOH to give the corresponding 3,4-dihydro-2 H-pyrrole derivatives 2 in moderate to excellent yields under reflux within a short time. As for the diarylvinylidenecyclopropane substrate containing a strongly electron-donating methoxy group on the benzene ring, the reaction leads to the formation of a different type of 3,4-dihydro-2 H-pyrrole derivatives 4 under the same conditions.     

Cu-catalyzed asymmetric [3+2] cycloaddition of α-iminoamides with activated olefins

A variety of 2-amido pyrrolidines, including Weinreb-type amides, have been prepared with very high exo diastereoselectivity and enantioselectivitiy in the reaction of α-iminoamides with activated alkenes catalyzed by Cu(I)-Segphos ligands.     

Ruthenium-catalyzed transfer oxygenative cyclization of α,ω-diynes: unprecedented [2 + 2 + 1] route to bicyclic furans via ruthenacyclopentatriene

A novel oxygen-atom-transfer process enables the catalytic [2 + 2 + 1] synthesis of bicyclic furans from α,ω-diynes with DMSO. [CpRu(AN)(3)]PF(6) catalyzed the transfer oxygenative cyclization of diynes with aryl terminal groups, while those of diynes with alkyl terminal groups were effectively promoted by the corresponding Cp* complex. A mechanism for bicyclic furan formation via a ruthenacyclopentatriene was proposed on the basis of both experimental and theoretical studies.     

Cobalt(I)-catalyzed [4π+2π] cycloaddition reactions of 1,3-diynes with 1,3,5-cyclooctatriene

The cycloaddition reaction between conjugated diynes and 1,3,5-cyclooctatriene in the presence of the catalyst Co(acac)₂/dppe/Zn/ZnI₂, led to the selective formation of tricyclo[4.2.2.0^2,5]deca-7,9-diene derivatives in 72–85% yield.     

Enantioselective rhodium-catalyzed [4+2] cycloaddition of α,β-unsaturated imines and isocyanates

A [4+2] cycloaddition of α,β-unsaturated imines and isocyanates catalyzed by a phosphoramidite-rhodium complex provides pyrimidinones in good yields and high enantioselectivities.     

[2+2+2] cycloaddition reactions of α,β-unsaturated N-arylaldimines,acetylenedicarboxylates and 2-arylidene-1,3-indanediones

The domino [2+2+2] cycloaddition reaction of α,β-unsaturated N-arylaldimines, dialkyl acetylenedicarboxylates and 2-arylidene-1,3-indanediones in dry methylene dichloride at room temperature afforded isomeric 2′-styryl-1,2′,3,4′-tetrahydro-1′H-spiro[indene-2,3′-pyridines] in good yields. Under similar conditions, the reaction of α,β-unsaturated N-arylaldimines with two molecules of dialkyl acetylenedicarboxylates resulted in 1-aryl-6-styryl-1,6-dihydropyridine-2,3,4,5-tetracarboxylates. Additionally, the three-component reaction of α,β-unsaturated N-arylaldimines, dimethylacetylenedicarboxylate and benzoyl cyanide also gave isomeric 1,3-oxazine-4,5-dicarboxylates.     

Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

Synthesis of optically active dihydropyrans from asymmetric [4 + 2] cycloaddition of β,γ-unsaturated α-ketoesters with allenic esters

β-Isocupreidine (β-ICD) catalyzed asymmetric [4 + 2] cycloaddition of β,γ-unsaturated α-ketoesters with allenic esters afforded ester-substituted functionalized dihydropyran derivatives in high yields along with high enantioselectivities under mild conditions.     

Pd-catalyzed addition-carbocyclization of α,ω-diynes with H-P(O)R2 compounds

Chelating phosphines are much higher performing than mono-dentate phosphines in palladium-catalyzed reaction of α,ω-diynes with HP(O)R¹R² (R¹,R² = Ph, alkoxy) to afford (E)-3-(phosphorylmethylene)-2-methylcyclopentenes.     

Iron-catalyzed intermolecular [2π+2π] cycloaddition

The bis(imino)pyridine iron dinitrogen compounds, ((iPr)PDI)Fe(N(2))(2) and [((Me)PDI)Fe(N(2))](2)(μ(2)-N(2)) ((R)PDI = 2,6-(2,6-R(2)-C(6)H(3)N═CMe)(2)C(5)H(3)N; R = (i)Pr, Me), promote the catalytic intermolecular [2π + 2π] cycloaddition of ethylene and butadiene to form vinylcyclobutane. Stoichiometric experiments resulted in isolation of a catalytically competent iron metallocycle intermediate, which was shown to undergo diene-induced C-C reductive elimination. Deuterium labeling experiments establish competitive cyclometalation of the bis(imino)pyridine aryl substituents during catalytic turnover.     

[6π+2π]-Cycloaddition of α,ω-Diallenes and α,ω-Diacetylenes to 1,3,5-Cycloheptatriene in the Presence of TiCl4-Et2AlCl

[6π+2π]-Cycloaddition of α,ω-diallenes and α,ω-bis(trimethylsilyl)diacetylenes to 1,3,5-cycloheptatriene in the presence of a two-component catalytic system TiCl₄-Et₂AlCl was performed that led to the formation of bis(endo-bicyclo[4.2.1]nona-2,4-dienes) and bis(8-trimethylsilyl-endo-bicyclo[4.2.1]nona-2,4,7-trienes) linked by polymethylene spacer in 69–86% yields.     

Intramolecular [2 + 2] photocycloaddition. 2. Mechanism of intramolecular photocyclization of α,ω-bis(p-vinylphenyl)alkanes

From the photophysical measurements of the title reaction, the formation of cyclophanes is concluded to be facilitated by high microscopic concentration of styrene moieties and depressed by strain loaded at the transition state.     

DMAP-catalyzed [4+2] annulation of α-substituded allenoates with unsaturated pyrazolones

A DMAP-catalyzed [4 + 2] annulation of α-substituted allenoates with unsaturated pyrazolones has been achieved in dichloromethane at 40 °C, providing multisubstituted tetrahydropyrano [2,3-c]pyrazoles in good to excellent yields with moderate to good Z/E ratios. The allenoates worked as two-carbon synthons in the reaction.     

Choline chloride–ZnCl2: Recyclable and efficient deep eutectic solvent for the [2+3] cycloaddition reaction of organic nitriles with sodium azide

Herein we report first time choline chloride–zinc chloride based deep eutectic solvent is a green and efficient reaction medium for the [2+3] cycloaddition reaction of organic nitriles with sodium azide to afford the corresponding 5-substituted 1H-tetrazoles. The present method provides an environment-friendly route, short reaction times with excellent yields, safe process, and simple workup which make this method an attractive and useful contribution to the existing conventional processes for the synthesis of 5-substituted 1H-tetrazoles.