Novel synthetic route to octasubstituted naphthalenes from four alkynes and one olefin unit via zirconacyclopentadienes and 1,2-diiodo-3,4,5,6-tetraalkylbenzene

1,2,3,4-Tetrasubstituted benzene derivatives were prepared by the reaction of zirconacyclopentadienes with vinyl bromide in the presence of NiCl(2)(PPh(3))(2). 1,2-Diiodo-3,4,5,6-tetraalkylbenzenes were formed by treatment of 1,2,3,4-tetraalkylbenzenes with iodine and periodic acid in the presence of a catalytic amount of sulfuric acid. Reaction of the 1,2-diiodo-3,4,5,6-tetraalkylbenzenes with zirconacyclopentadienes in the presence of a stoichiometric amount of CuCl gave sterically crowded octasubstituted naphthalenes in moderate yields.     

Cycloaddition of Zirconacyclopentadiene with 2-Bromoacrylate, 2-Bromoacrylaldehyde,and 3-Bromofuran-2,5-dione in the Presence of CuCl: A New Pathway for the Formation of Benzene Derivatives and Isobenzofuran-1,3-dione

Reaction of zirconacyclopentadienes with 2-bromoalkenes in the presence of CuCl afforded multisubstituted benzene derivatives. The reactions of 2-bromoacrylate and 2-bromo-3-phenylacrylaldehyde afforded penta- and hexasubstituted benzenes in good yields. The reaction of 3-bromofuran-2,5-dione with zirconacyclopentadienes gave isobenzofuran-1,3-diones in good yields.     

Remarkable effect of copper chloride on diiodination of zirconacyclopentadienes

Treatment of zirconacyclopentadienes with two equiv of iodine in THF in the presence of 1.0 equiv of CuCl gave diiododienes in good to high yields without formation of monoiododienes. This is in sharp contrast to the case without CuCl which afforded monoiododienes as major products. For zirconacyclopentenes, CuCl was also effective but the use of ICI was more practical. When zirconacyclopentenes were treated with 2 equiv of ICI, only diiodination products were formed. Preparation of silacyclopentadienes or spiro compounds using the diidodienes was demonstrated.     

Cu(I)-mediated reductive amination of boronic acids with nitroso aromatics

[reaction: see text] A mild method for the reductive amination of aryl boronic acids with nitroso aromatic compounds is reported. This C-N bond formation is mediated by a stoichiometric amount of CuCl as both a catalyst and a reducing agent. Alternatively, 10% Cu(I)-3-methylsalicylate (CuMeSal) catalyzes the same reaction in the presence of either ascorbic acid or hydroquinone as the terminal reducing agent. Diarylamines bearing a variety of functional groups can be obtained in good yields.     

1,1-Cycloaddition of oxalyl dichloride with dialkenylmetal compounds: formation of cyclopentadienone derivatives by the reaction of 1,4,-dilithio-1,3-dienes or zirconacyclopentadienes with oxalyl chloride in the presence of CuCl

1,4-Dilithio-1,3-dienes or zirconacyclopentadienes reacted with oxalyl chloride in the presence of CuCl in a 1,1-cycloaddition manner to give cyclopentadienone derivatives in high yields along with the elimination of CO.     

Reactions of zirconacyclopentadienes with C [double bond] ), C [double bond] N, and N [double bond] N moieties with electron-withdrawing groups: formation of six-membered heterocycles

Reactions of zirconacyclopentadienes with diethyl ketomalonate gave alpha-pyrans in excellent yields in the presence of BiCl3. In the absence of BiCl3, zirconacyclopentadienes did not react with diethyl ketomalonate. Tetraphenylzirconacyclopentadiene reacted with diethyl ketomalonate in the presence of BiCl3 to give a ring-opening product, dienolic ether, in 53% yield. The structures of the alpha-pyran prepared from diethyldiphenylzirconacyclopentadiene and the ring-opening product were determined by X-ray analysis. When oximinosulfonate was added to tetraethylzirconacyclopentadiene in THF at -78 degrees C, 3,4,5,6-tetraethylpyridine-2-carbonitrile was obtained in 95% yield within 10 min. The structure of the product was confirmed by X-ray analysis. When tetraethylzirconacyclopentadiene was treated with azodicarboxylate in the presence of 2 equiv of CuCl at -78 degrees C, 1,2-dialkoxycarbonyl-3,4,5,6-tetraethyl-1,2-dihydropyridazine derivatives were obtained. The structure of one of dihydropyridazine was also confirmed by X-ray analysis.     

Palladium-catalyzed synthesis of 1,2,3,4-tetraalkyl-1,4-diarylbutadienes by cross-coupling of zirconacyclopentadienes with aryl iodides

A novelmethod for the synthesis of 1, 2, 3, 4-tetraalkyl-1, 4-diarylbutadienes was developed via palladiumcatalyzed cross-coupling of zirconacyclopentadienes with aryl iodides. Equivalent of CuCl was introduced to promote the reaction. The desired products were obtained in good to excellent yields and several of them were reported for the first time.     

Effect of lithium chloride on allylation of zirconacyclopentadienes

The effects of lithium chloride on the allylation of zirconacyclopentadienes with allylic halides in the presence of CuCl have been studied. It is found that mono-allylation products are formed predominantly in the absence of lithium chloride, while the presence of lithium chloride leads to the formation of di-allylation products.     

Lewis acid-controlled reactions of zirconacyclopentadienes with isocyanates and isothiocyanates. One-pot three- or four-component synthesis of multiply substituted iminocyclopentadienes and butadiene-tethered 1,6-bisamides and electrophilic cyclization

Multiply substituted zirconacyclopentadienes including bicyclic zirconacyclopentadienes and zirconaindenes reacted with isocyanates and isothiocyanates in the presence of Lewis acids to afford iminocyclopentadienes and conjugated 1,6-bisamides, depending on the nature of Lewis acids, isocyanates, and isothiocyanates used. Only in the presence of BF₃ could iminocyclopentadienes be obtained in high isolated yields when zirconacyclopentadienes were treated with isocyanates. On the contrary, BF₃ could not mediate the reaction of zirconacyclopentadienes with isothiocyanates. For the reactions of zirconacyclopentadienes with isothiocyanates, EtAlCl₂ was found effective to generate iminocyclopentadienes as the products. Interestingly, however, for the reactions of zirconacyclopentadienes with isocyanates, EtAlCl₂ was found to work very differently from BF₃. Instead of iminocyclopentadienes, conjugated 1,6-bisamides and conjugated mono-amides were obtained as products in high isolated yields from the reactions of zirconacyclopentadienes with isocyanates, depending on the substituents of isocyanates. The reaction path and products could be controlled by Lewis acids. As a demonstration of the usefulness of thus obtained unsaturated bisamides, electrophilic cyclization using acids, NBS, and I₂ was carried out. Electrophilic cyclization of multisubstituted conjugated 1,6-bisamide derivatives afforded cyclic iminoethers in excellent yields with perfect selectivity. Only one of the amide groups took part in the electrophilic cyclization.     

Oxidative transformations of phenylacetylene in a Ph3MF2 (M=Bi, Sb)−CuCl system

The composition of products of the reaction of phenylacetylene with Ph₃BiF₂ and Ph₃SbF₂ in the presence of CuCl is considerably affected by the amount of the promoter. When the molar ratio phenylacetylene: CuCl is 1:1, the major product is diphenylacetylene; a decrease in amount of CuCl to 10 mol. % results in an increase in the yield of tolan to 60%.     

ZnCl2 and CuCl promoted aldol reactions of isocyanoacetate with α,β-unsaturated carbonyl compounds

Reaction of ethyl isocyanoacetate with α,β-unsaturated carbonyl compounds was promoted by a stoichiometric amount of ZnCl₂ or a catalytic amount of CuCl/Et₃N (1:1) to give 5-alkenyl-4-carboethoxyoxazolines (3) in moderate yields. The oxazolines (3) were converted by palladium catalyst to 2-formamino-2,4-alkadienoic acid ethyl esters (5).     

Nucleophilic additions of arylzinc compounds to aldehydes mediated by CrCl(3): efficient and facile synthesis of functionalized benzhydrols, 1(3H)-isobenzofuranones, benzyl alcohols, or diaryl ketones

In the presence of a stoichiometric amount of CrCl(3) and trimethylchlorosilane (TMSCl), nucleophilic addition of arylzinc compounds 1c-h to arylaldehydes 2a,b,g smoothly proceeded at room temperature to yield corresponding benzhydrols 4a-f in good yields. From arylzinc compounds 1a,b, 3-aryl-1(3H)-isobenzofuranones 3a-f were given by the CrCl(3)-mediated reaction with arylaldehydes 2a-f. Diaryl ketones 5a-e were obtained in good yields by the addition of excess amount of benzaldehyde as an oxidant to the resulting solution after the CrCl(3)-mediated reaction between arylzinc compounds 1c-g and arylaldehydes 2b,g was completed. In the nucleophilic additions of arylzinc compounds 1a,d,f to alkyladehydes 6b-f, the treatment of arylzinc compounds with CrCl(3) was required prior to the addition of the aldehydes in order to prevent the fast protodezincation of arylzinc compounds by the enolizable aldehydes. In these CrCl(3)-mediated nucleophilic additions of arylzinc compounds to aldehydes, arylchromium(III) species are probably reactive intermediates.     

Palladium-catalyzed intramolecular hydroalkylation of alkenyl-beta-keto esters, alpha-aryl ketones, and alkyl ketones in the presence of Me3SiCl or HCl

Reaction of 3-butenyl beta-keto esters or 3-butenyl alpha-aryl ketones with a catalytic amount of [PdCl2(CH3CN)2] (2) and a stoichiometric amount of Me3SiCl or Me3SiCl/CuCl2 in dioxane at 25-70 degrees C formed 2-substituted cyclohexanones in good yield with high regioselectivity. This protocol tolerated a number of ester and aryl groups and tolerated substitution at the allylic, enolic, and cis and trans terminal olefinic positions. In situ NMR experiments indicated that the chlorosilane was not directly involved in palladium-catalyzed hydroalkylation, but rather served as a source of HCl, which presumably catalyzes enolization of the ketone. Identification of HCl as the active promoter of palladium-catalyzed hydroalkylation led to the development of an effective protocol for the hydroalkylation of alkyl 3-butenyl ketones that employed sub-stoichiometric amounts of 2, HCl, and CuCl2 in a sealed tube at 70 degrees C.     

Cu-facilitated C-O bond formation using N-hydroxyphthalimide: efficient and selective functionalization of benzyl and allylic C-H bonds

A highly efficient protocol for the benzyl or allylic C-H functionalization of simple hydrocarbons has been developed using stoichiometric amounts of N-hydroxyphthalimide and PhI(OAc)2 in the presence of CuCl catalyst. The reaction was revealed to proceed via a radical pathway, in which phthalimide N-oxyl (PINO) radical plays a dual role, serving as a catalytic hydrogen abstractor from hydrocarbons as well as a stoichiometric reagent to couple with the resultant alkyl radicals.     

Coupling reaction of zirconacyclopentadienes with dihalonaphthalenes and dihalopyridines: a new procedure for the preparation of substituted anthracenes, quinolines, and isoquinolines.

Reactions of tetraiodobenzene with zirconacyclopentadienes, which were conveniently prepared from two alkynes (or diynes) and zirconocene complexes, afforded 1,2,3,4-tetrasubstituted diiodonaphthalene derivatives in good isolated yields. These 1,2,3,4-tetrasubstituted diiodonaphthalene derivatives could be converted to 1,2,3,4,5,6,7,8-octasubstituted anthracene derivatives by reaction with a second zirconacyclopentadiene. When the two zirconacyclopentadienes were different, unsymmetrical anthracenes such as 1,2,3,4-tetraethyl-5,6,7,8-tetraphenylanthracene (68% isolated yield) were obtained. On the other hand, treatment of a 2,3-dihalopyridine such as 2-bromo-3-iodopyridine with zirconacyclopentadienes gave 5,6,7,8-tetrasubstituted quinoline derivatives in good to high yields. 3,4-dihalopyridines such as 4-chloro-3-iodopyridine reacted with zirconacyclopentadienes to afford 5,6,7,8-tetrasubstituted isoquinoline derivatives in good to high yields.     

Conjugate reduction of alpha,beta-unsaturated carbonyl compounds catalyzed by a copper carbene complex

[reaction: see text] An N-heterocyclic carbene copper chloride (NHC-CuCl) complex (2) has been prepared and used to catalyze the conjugate reduction of alpha,beta-unsaturated carbonyl compounds. The combination of catalytic amounts of 2 and NaOt-Bu with poly(methylhydrosiloxane) (PMHS) as the stoichiometric reductant generates an active catalyst for the 1,4-reduction of tri- and tetrasubstituted alpha,beta-unsaturated esters and cyclic enones. The active catalytic species can also be generated in situ from 1,3-bis(2,6-di-isopropylphenyl)-imidazolium chloride (1) CuCl(2).2H(2)O in the presence of NaOt-Bu and PMHS.     

Scope and mechanism of the Pd(II)-catalyzed arylation/carboalkoxylation of unactivated olefins with indoles

Treatment of 1-methyl-2-(4-pentenyl)indole (5) with a catalytic amount of [PdCl2(MeCN)2] (2; 5 mol %) and a stoichiometric amount of CuCl2 (3 equiv) in methanol under CO (1 atm) at room temperature for 30 min gives methyl (9-methyl-2,3,4,9-tetrahydro-4-carbazolyl)acetate (6), which was isolated in 83% yield. A number of 2- and 3-alkenyl indoles undergo a similar palladium-catalyzed cyclization/carboalkoxylation to give the corresponding polycyclic indole derivatives in moderate to excellent yields with excellent regio- and diastereoselectivity. Under similar conditions, vinyl arenes undergo intermolecular arylation/carboalkoxylation with indoles to give 3-(1-aryl-2-carbomethoxyethyl) indoles in moderate yield with high regioselectivity. Stereochemical analyses of the palladium-catalyzed cyclization/carboalkoxylation of both 2- and 3-alkenyl indoles are in agreement with mechanisms involving outer-sphere attack of the indole on a palladium-olefin complex followed by alpha-migratory insertion of CO and methanolysis of the resulting acyl palladium intermediate. CuCl2 functions as the terminal oxidant in this palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles and also significantly increases the rate of reaction of 2 with the alkenyl indole to form the corresponding acyl palladium complex. Spectroscopic studies are in agreement with the intermediacy of a heterobimetallic Pd/Cu complex as the active catalyst in this reaction.     

Selective synthesis of fused cyclooctatetraenes by [4 + 4] coupling between two different diene units

In the presence of CuCl and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, the [4 + 4] coupling between zirconacyclopentadienes and 1,3-diiodobutadienes fused through an oxygen or nitrogen five-membered ring proceeded at ambient temperature to afford fully substituted polycyclic cyclo-octatetraenes in good yields. The fused ring moiety of the diiodides plays a critical role. The corresponding acyclic diiodide and a cyclohexane-fused analogue gave no coupling product, and a cyclopentane derivative showed only moderate reactivity. Correlation of the structures of the diiodides and their reactivity was established by an X-ray and density functional study.     

Palladium-catalyzed intramolecular oxidative alkylation of 4-pentenyl beta-dicarbonyl compounds

Reaction of 8-nonene-2,4-dione with a catalytic amount of [PdCl2(CH3CN)2] (2; 5 mol %) and a stoichiometric amount of CuCl2 (2.5 equiv) at room temperature for 3 h led to oxidative alkylation and formation of 2-acetyl-3-methyl-2-cyclohexenone in 80 % isolated yield. The oxidative alkylation of 4-pentenyl beta-diketones tolerated a number of terminal acyl groups and substitution at the C1 and C3 carbon atoms of the 4-pentenyl chain. Likewise, 4-pentenyl beta-keto esters that possessed geminal disubstitution at the C1, C2, or C3 carbon atom of the 4-pentenyl chain cyclized to form 2-carboalkoxy-2-cyclohexenones in moderate to good yield as the exclusive cyclized product. Deuterium-labeling experiments provided information regarding the mechanism of the palladium-catalyzed oxidative alkylation of 4-pentenyl beta-dicarbonyl compounds.     

Palladium-catalyzed oxidative alkoxylation of alpha-alkenyl beta-diketones to form functionalized furans

Treatment of 4-allyl-2,6-dimethyl-3,5-heptanedione with a catalytic amount of PdCl(2)(CH(3)CN)(2) (5 mol %) and a stoichiometric amount of CuCl(2) (2.2 equiv) in dioxane at 60 degrees C for 12 h formed 3-isobutyryl-2-isopropyl-5-methylfuran in 77% isolated yield. A number of alpha-alkenyl beta-diketones underwent oxidative alkoxylation under these conditions to form 2,3,5-trisubsituted furans in moderate to good yield.