Reaction of ene-bis(phosphinylallenes): [2+2] versus [4+2] cycloaddition

Reaction of ene-bis(phosphinylallenes), derived from ene-bis(propargyl alcohols) and chlorodiphenylphosphine, was investigated. Benzene-bridged bis(phosphinylallenes) exclusively gave intramolecular [2+2] cycloadducts in the presence of dimethyl fumarate in sharp contrast to the reaction of benzene-bridged bis(sulfinylallenes), which gave the corresponding [4+2] cycloadducts. On the other hand, substituted ethylene- or five-membered heterocycle-bridged bis(phosphinylallenes) provided [4+2] cycloadducts. Reaction of benzene-bridged diallene bearing both a sulfinyl group and a phosphinyl group on the two allenyl groups was also described.     

Intermolecular dearomative [4 + 2] cycloaddition of naphthalenes via visible-light energy-transfer-catalysis

The dearomative cycloaddition reaction serves as a blueprint for creating sp³-rich three-dimensional molecular topology from flat-aromatic compounds. However, severe reactivity and selectivity issues make this process arduous. Herein, we describe visible-light energy-transfer catalysis for the intermolecular dearomative [4 + 2] cycloaddition reaction of feedstock naphthalene molecules with vinyl benzenes. Tolerating a wide range of functional groups, structurally diverse 2-acyl naphthalenes and styrenes could easily be converted to a diverse range of bicyclo[2.2.2]octa-2,5-diene scaffolds in high yields and moderate endo-selectivities. The late-stage modification of the derivatives of pharmaceutical agents further demonstrated the broad potentiality of this methodology. The efficacy of the introduced methods was further highlighted by the post-synthetic diversification of the products. Furthermore, photoluminescence, electrochemical, kinetic, control experiments, and density-functional theory calculations support energy-transfer catalysis.

Constructing 3D molecular scaffolds from aromatic hydrocarbons is challenging. Herein, we report dearomative [4 + 2] cycloaddition reaction of naphthalenes via visible-light EnT catalysis which overcomes issues of unfavorable thermodynamics, low yields, and selectivity.     

Catalytic [2+2+2] and thermal [4+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes

We have determined that a cationic rhodium(I)/Segphos complex catalyzes an enantio- and diastereoselective intermolecular [2+2+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes with various monoalkynes at room temperature to give axially chiral 1,4-teraryls possessing an anthraquinone structure in good yields with good enantio- and diastereoselectivities. We have also determined that a thermal intramolecular [4+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes proceeds at 60 degrees C to give aryl-substituted naphthacenediones in moderate to good yields.     

[4+2]cycloaddition reactions of triarylphosphaalkene

Cycloaddition reactions of mesityl(diphenyliiifithylene)phosphine ($\text{1}$) were Investigated. With several dienes, no Diels-Alder reactions were oEserved. With azides, diphenyidiazomethane and 2,4,6-trimethylbenzonitrile oxide, the corresponding cycloadducts ($\text{4}$$\text{12}$$\text{17}$$\text{12}$were obtained. In the case of phenyl azide, a competing Staudinger reaction occurred leading to $\text{3}$.     

Rhodium N-heterocyclic carbene-catalyzed [4 + 2] and [5 + 2] cycloaddition reactions

[reactions: see text] A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels-Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions, all the dienynes studied were converted to their corresponding cycloadducts in 91-99% yields within 10 min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at 15-20 degrees C. For the intermolecular [4 + 2] cycloadditions, high yields (71-99%) of the corresponding cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes studied were converted to their corresponding cycloadducts in 91-98% yields within 10 min. However, the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.     

Catalytic enantioselective [2 + 4] and [2 + 2] cycloaddition reactions with propiolamides

We report here the catalytic and highly enantioselective [2 + 4] and [2 + 2] cycloaddition reactions of electron-rich dienes or silyl enol ethers with electron-deficient propiolamide derivatives induced by copper(II).3-(2-naphthyl)-L-alanine amide complex.     

Intramolecular [4+2] cycloaddition of an indolenine

Attempted transformation of readily accessible 18-methylenevincadifformine (I) to indolenine VI in acidic medium afforded unexpectedly the intramolecular [4+2] cycloadduct VIII in almost quantitative yield     

Intermolecular transition metal-catalyzed [4 + 2 + 2] cycloaddition reactions: a new approach to the construction of eight-membered rings

Transition metal-catalyzed cycloaddition reactions represent powerful methods for the construction of complex polycyclic systems. We have developed a new intermolecular metal-catalyzed [4 + 2 + 2] cycloaddition of heteroatom-tethered enyne derivatives with 1,3-butadiene. This study demonstrates that excellent selectivity can be obtained for the heterocycloaddition adducts through the judicious choice of silver salt. The development of the tandem rhodium-catalyzed allylic substitution [4 + 2 + 2] cycloaddition provides a convenient three-component coupling that circumvents the prior formation of the enyne derivative. Finally, the introduction of a stereogenic center at C-2 leads to a diastereoselective cycloaddition, which provides a powerful new method for the construction of bicyclic octanoid ring systems applicable to target directed synthesis.     

[4+2] cycloaddition of intermediates generated from arynes and DMF

The trapping reaction of the transient intermediate ortho-quinone methides, generated by the insertion of arynes into a carbon–oxygen double bond of DMF, with dienophiles was investigated. The [4+2] cycloaddition products were obtained when the diesters of acetylenedicarboxylic acid were employed as dienophiles.     

[2+2]- AND [4+2] cycloaddition reactions of 1,3-diazabutadienes with diphenylketene

1,3-Diazabutadienes react with diphenylketene in [2+2] - and [4+2] cycloaddition reactions, depending on the substitution pattern. Spectroscopic data (IR, ¹H- and ¹³C-NMR) and results of quantummechanical model calculations (ab initio 3-21G) are presented.     

Rhodium-Catalyzed Intermolecular [4+2] Cycloaddition of Unactivated Substrates

No electron-withdrawing or electron-releasing substituents are necessary for the substrates in the rhodium-catalyzed [4+2] cycloaddition reaction between a vinylallene and an ordinary alkyne under mild conditions [Eq. (1)]. The use of the strongly electron-accepting P[OCH(CF₃)₂]₃ ligand affords the optimal rhodium catalyst. cod = 1,5-cyclooctadiene.     

Stereochemistry of the [2+4] cycloaddition of cyclopentyne

The [2+4] cycloaddition of cyclopentyne with a pair of diastereomeric 1,3-dienes is found to occur with high stereoselectivity. The results support the applicability of the principles of orbital symmetry even in the case of this exceedingly reactive dienophile.     

Synthesis of isoindolinones: Intramolecular [4+2] cycloaddition/retro [4+2] of pyridone propiolamides

A new synthesis of isoindolinones was discovered during a screening campaign aimed at the development of novel methods for the synthesis of pyridone-EZH2 inhibitor analogues. The reaction proceeds via an intramolecular [4+2] cycloaddition of a pyridone with a tethered propiolamide moiety followed by extrusion of isocyanic acid. The discovery, optimization, and scope of the methodology are described.     

Nickel-catalyzed [4+2] cycloaddition for highly substituted arenes

Nickel(0) catalyzed [4+2] cycloaddition of electron-deficient dienes to alkynes and subsequent aromatization gave highly substituted arenes. This formal inverse electron-demand Diels-Alder cycloaddition is attributed to the formation of a seven-membered nickelacycle from a diene and an alkyne.     

Au(PPh3)OPOF2-catalyzed intramolecular [4+2] cycloaddition reaction of dienynes

Solvolysis of Au(PPh(3))PF(6) afforded Au(PPh(3))OPOF(2) which is an effective catalyst in the intramolecular [4+2] cycloaddition of unactivated dienynes bearing a terminal alkyne.     

Synthesis of C-arylglycosides via Ru(II)-catalyzed [2 + 2 + 2] cycloaddition

In the presence of catalytic amounts of Cp*RuCl(cod), the cycloaddition of 1,6-diynes with various C-alkynylglycosides proceeded at ambient temperature to afford C-arylglycosides in 46-93% yields.