Ru(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,2-bis(propiolyl)benzenes with monoalkynes leading to substituted anthraquinones

[2 + 2 + 2] cycloadditions of 1,2-bis(propiolyl)benzenes with monoalkynes were effectively catalysed by Cp*RuCl(cod) under mild conditions to give substituted anthraquinones in moderate to high yields.     

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.     

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.     

Lewis acid-catalyzed benzannulation via unprecedented [4+2] cycloaddition of o-alkynyl(oxo)benzenes and enynals with alkynes

The reaction of o-alkynyl(oxo)benzenes 1 with alkynes 2 in the presence of a catalytic amount of AuCl(3) in (CH(2)Cl)(2) at 80 degrees C gave the [4+2] benzannulation products, naphthyl ketone derivatives 3 and 4, in high yields. When the reaction was carried out using AuBr(3) instead of AuCl(3), the reaction speed was enhanced and the chemical yield was increased. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(OTf)(2) and 1 equiv of a Br?nsted acid, such as CF(2)HCO(2)H, in (CH(2)Cl)(2) at 100 degrees C, the decarbonylated naphthalene products 5 were obtained in high yields. Similarly, the Cu(OTf)(2)-H(2)O-promoted reaction of the enynals 7 with an alkyne 2 afforded the corresponding [4+2] benzannulation products, decarbonylated benzene derivatives 8, in good yields. Both AuX(3)- and Cu(OTf)(2)-catalyzed benzannulations proceed most probably through the formation of the benzo[c]pyrylium ate complex 10, the Diels-Alder addition of alkynes 2 to the ate complex, and the resulting bicyclic pyrylium ion intermediate 12. The mechanistic difference between the AuX(3) and Cu(OTf)(2)-HA system is discussed.     

Bay-area selective thermal [4+2] and [4+4] cycloaddition reactions of triply linked ZnII diporphyrin with o-xylylene

A triply linked ZnII diporphyrin underwent site-selective cycloaddition reactions with thermally generated o-xylylene to provide a triply linked porphyrin-chlorin hybrid and a triply linked chlorin dimer in moderate yields. The former product is a symmetry-allowed [4+2] cycloadduct, while the latter is a symmetry-forbidden [4+4] cycloadduct. Oxidation of the latter product with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) provided a triply linked diporphyrin fused with a benzocyclooctatriene segment. This oxidized product and above [4+2] cycloadduct were structurally characterized by single crystal X-ray diffraction analysis. The observed site-selectivity is considered to arise from the large MO coefficients at the bay-area in the LUMO of the triply linked diporphyrin. The anomalous thermal [4+4] cycloaddition may be ascribed to the highly conjugated and quite perturbed electronic properties of triply linked ZnII diporphyrin.     

Synthesis of naphtho[b]cyclobutenes from 1,2-bis(3-propynol)benzenes

We have demonstrated that the reaction of benzene-bridged bis(propargyl alcohol)s with chlorodialkylphosphines exclusively afforded 3,8-bis(dialkylphosphinyl)naphtho[b]cyclobutenes via the [2+2] cycloaddition of 1,2-bis(α-phosphinylallenyl)benzenes. Dephosphinylation of the product has also been achieved.     

Catalytic [2+2] and [3+2] cycloaddition reactions of allenoates with cyclic ketimines

Cyclic ketimines as electrophiles for [2+2] and [3+2] cycloaddition reactions of allenoates have been developed, affording functionalized sultam-fused azetidines and dihydropyrroles, respectively, in good yields with high regioselectivities.     

New synthesis of 1,2-bismethylenecyclobutanes by [2+2] cycloaddition reaction of 1,1-diphenyl-4,4-bis(trifluoromethyl)-butatriene with electron-rich alkenes

The title compound 1 undergoes thermal [_π2_S+_π2_S] cycloaddition reactions with 1,1-dimethoxyethylene or enamines to produce 1,2-bismethylenecyclobutanes of type 3.     

(1+1) or (2+2) Coupling for bis(tosyloxyethoxy)benzenes with calix[4]arene and thiacalix[4]arene

As bifunctional reagents, bis(tosyloxyethoxy)benzenes can react with p-tert-butylcalix[4]arene or p-tert-butylthiacalix[4]arene to afford intramolecularly bridged (1+1) or intermolecularly bridged (2+2) products. It was found that the bridging pattern strongly depended on the structure of bis(tosyloxyethoxy)benzene and the kind of calixarene. For the ortho-isomer of bis(tosyloxyethoxy)benzene, intramolecularly bridged calix[4]arene and thiacalix[4]arene were the main products. For the para-isomer, the bridging reaction was in a (2+2) fashion. As for the meta-isomer, double thiacalix[4]arene and intramolecularly bridged calix[4]crown were synthesized.     

[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 [2+1] cycloaddition of diazo compounds to [60]fullerene

A catalytic method for the efficient synthesis of 5,6-open and 6,6-closed (2π+1π) fullerene adducts by [2+1] cycloaddition of ethyl 2-alkyl(hetaryl)-2-diazoacetates to [60]fullerene in the presence of a three-component catalyst Pd(acac)₂—PPh₃—Et₃Al have been developed.     

Preparation,structure, and unique thermal [2+2], [4+2], and [3+2] cycloaddition reactions of 4-vinylideneoxazolidin-2-one

The terminal allene C(alpha)=C(beta) bonds of 4vinylidene-2-oxazolidinone (2) readily undergo [2+2] cycloaddition with a wide variety of terminal alkynes, alkenes, and 1,3-dienes irrespective of their electronic nature under strictly thermal activation conditions (70-100 degrees C) and provide 3substituted (Z)-methylenecyclobutenes 6, 3substituted methylenecyclobutanes 7 and 8, and 3vinylmethylenecyclobutanes 9, respectively, in good to excellent yields. Alkenes react with 2 with complete retention of configuration. The [2+2] cycloaddition is concluded to proceed via a concerted [(pi(2s)+pi(2s))(allene) + pi(2s)] Hückel transition state on the basis of experimental evidences and quantum mechanical methods. Some highly polarized enones and nitrile oxide, on the other hand, react with 2 selectively at the internal C(4)=C(alpha) double bonds and give spiro compounds 10 and 11, respectively. The bent allene bonds (173-176 degrees) and the unique reactivity associated with 2 are attributed to a low-lying LUMO (C(alpha)=C(beta)) that is substantiated by a through-space sigma*(N-SO(2))-pi*(C(alpha)=C(beta)) orbital interaction.     

Intermolecular [4 + 2] cycloaddition of o-quinodimethanes derived from ene-bis(sulfinylallenes)

Intermolecular [4 + 2] cycloaddition of o-quinodimethanes, prepared in situ from ene-bis(propargyl alcohols) and benzenesulfenyl chloride via ene-bis(sulfinylallene) formation, was investigated. Benzene-bridged bis(propargyl alcohols) reacted with both electron-deficient and electron-rich olefins to give the corresponding [4 + 2] cycloadducts. Ethylene-bridged bis(propargyl alcohols) underwent similar cycloaddition with electron-deficient olefins. Construction of some heterocycles based on the newly developed sequential reaction is also described.     

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     

Catalytic enantioselective intermolecular [2 + 2 + 2] cycloaddition of an alkene and two alkynes

A catalytic enantioselective intermolecular [2 + 2 + 2] cycloaddition of one molecule of alkene (enone) and two molecules of alkyne was developed in the presence of a nickel complex modified by chiral monodentate oxazoline ligands, which have not previously been used as chiral ligands for transition metals in asymmetric catalysts, and an aluminium phenoxide.     

Crystal chemistry of protonated 1,2-bis(di-R-aminomethyl)benzenes. Part V. [1,2-bis(diethylaminomethyl)-3,6-dichlorobenzene:1,2-bis(diethylaminomethyl)-3,4,6-trichlorobenzene]perchlorate mixed crystals

The mixed crystals of 1,2-bis(diethylaminomethyl)-3,6-di- and 3,4,6-trichloro-benzene perchlorate at 0.5:0.5 ratio have been studied using X-ray diffraction and FT-IR spectroscopy. The molecules of di- and tri-chloro derivatives are distributed randomly in the crystal lattice; however, this disorder manifested mainly by a partial occupation of the chlorine atom at C(4) and by relatively big atomic temperature parameters even at 99 K, particularly for the oxygens of the perchlorate anion. The proton in the [NHN]⁺ bond refined close to the equidistant position between the nitrogens. The conformations of the diethylaminomethyl substituents are pseudo-symmetrical relative to the plane and twofold axis passing through the midpoint of the hydrogen bond. The IR spectrum of the crystals shows a broad intense band and an intense continuous absorption indicating relatively high proton polarizability in the intramolecular hydrogen bond. In acetonitrile and in chloroform, the proton in the intramolecular hydrogen bond also shows a very high proton polarizability demonstrated by the continuous absorption in the IR spectrum.