Divergent Reactivity of Homologue ortho‐Allenylbenzaldehydes Controlled by the Tether Length: Chromone versus Chromene Formation

The divergent behavior of two homologue allenals, namely, 2‐(buta‐2,3‐dienyloxy)‐ and 2‐(propa‐1,2‐dienyloxy)benzaldehydes, as cyclization substrates is described. 2‐(Buta‐2,3‐dienyloxy)benzaldehydes suffers a formal allenic carbocyclization reaction to afford chromenes, whereas 2‐(propa‐1,2‐dienyloxy)benzaldehydes react to yield chromones. The formation of chromenes is strictly a formal hydroarylation process divided into two parts, namely, allenic Claisen‐type rearrangement and oxycyclization. An unknown N‐heterocyclic carbene (NHC)‐catalyzed allenic hydroacylation reaction must be invoked to account for the preparation of chromones. ortho‐Allenylbenzaldehydes bearing either electron‐donating substituents or electron‐withdrawing substituents worked well to afford both the hydroarylation and hydroacylation products. This unexpected difference in reactivity can be rationalized by means of density functional theory calculations.     

Trifluoroacetic acid-mediated hydroarylation: synthesis of dihydrocoumarins and dihydroquinolones

[reaction: see text] Trifluoroacetic acid mediates the hydroarylation of alkenes to afford dihydrocoumarins and dihydroquinolones in good yield. Intermolecular hydroarylation of cinnamic acids by phenols is particularly facile, which leads to the conclusion that previous reports of palladium-catalyzed hydroarylation of cinnamic acids in trifluoroacetic acid are erroneous.     

Nickel(0)‐Catalyzed Hydroarylation of Styrenes and 1,3‐Dienes with Organoboron Compounds

A Ni‐catalyzed hydroarylation of styrenes and 1,3‐dienes with organoboron compounds has been developed. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox‐neutral conditions. In this hydroarylation reaction, a new strategy that uses the proton of methanol to generate the active catalyst species Ni?H was developed. The Ni‐catalyzed hydroarylation, combined with a Ir‐catalyzed C?H borylation, affords a very efficient and straightforward access to a retinoic acid receptor agonist.     

Chemical libraries via sequential C-H functionalization of phenols

Phenols provide a useful template for diversification via sequential hydroarylation reactions. Specifically, a protocol has been developed that begins with the hydroarylation of cinnamic acids by 3,5-dimethoxyphenol to produce dihydrocoumarins. This activated ester undergoes facile ring-opening with amines to form a C-N bond and regenerate a phenol. The resulting phenol can be further functionalized via a second hydroarylation reaction. Thus, in 3-4 steps, a phenol is coupled with a cinnamic acid, an amine, and a cinnamic or propiolic acid.     

Pt(II)-catalyzed hydroarylation reaction of alkynes with pyrroles and furans

A Pt(II) catalyst showed a drastic effect on hydroarylation of alkynes with pyrroles and furans compared with Pd(OAc)₂ catalyst. The hydroarylation reactions proceeded smoothly under mild conditions to give double-hydroarylation products in good yields. Mono-adducts were formed only when the second hydroarylation was inhibited by steric hindrance of substrates or low reactivity of the mono-adducts.     

Palladium-catalyzed hydroarylation of alkynes with arenediazonium salts

The palladium-catalyzed hydroarylation of arenediazonium tetrafluoroborates with alkynes in the presence of triphenylsilane affords stereoselectively hydroarylation products in moderate to high yields. The reaction tolerates a variety of substituents including keto, ester, cyano, and nitro groups and can be performed as a one-pot procedure generating the arenediazonium salt in situ. With ethyl phenylpropynoate as the starting alkyne, the hydroarylation affords ethyl (Z)-2-arylcinnamates stereo- and regioselectively.     

Highly efficient iodine-catalyzed hydroarylation of arenes with styrenes

Iodine mediates the hydroarylation of styrenes with arenes and heteroarenes to afford 1,1-diarylalkanes in good to high yields. Details regarding the substrate scope and selectivity of this hydroarylation reaction are discussed.     

联二烯丁基硫醚衍生物合成呋喃的反应

本文报道以联二烯丁基硫醚为起始物的呋喃衍生物的合成方法.实验结果表明,β-联二烯丁基硫醚醇在氢化钠的作用下以很高的收率环化生成一个苯硫基离去的呋喃产物,β-联二烯丁基硫醚醛与外加亲核试剂作用后能得到多一个取代的类似呋喃产物,而β-联二烯丁基硫醚酮在P2O5的促进下也能环化生成呋喃衍生物.     

A high hydroarylation activity of K2PtCl4/AgOTf catalyst in the reaction of propiolic acid with unactivated and activated arenes

A mixed catalyst K₂PtCl₄/AgOTf showed the highest activity for hydroarylation of propiolic acid, among palladium and platinum catalysts. This catalyst was effective for hydroarylation with less reactive benzene to give cis-cinnamic acid in good yield. The hydroarylation with toluene gave a higher yield of hydroarylation products than that with benzene and resulted in ortho/para orientation with an almost statistical ratio, suggesting that the result is very close to that of the Friedel-Crafts alkylation with methyl bromide or p-nitrobenzyl chloride. Hydroarylation of propiolic acid with other electron-rich arenes proceeded efficiently in the presence of the K₂PtCl₄/AgOTf catalyst in trifluoroacetic acid forming cis-cinnamic acids in good to high yields. This method was also applied to hydroarylation of ethyl propiolate.     

Dearomative spirocyclization via visible-light-induced reductive hydroarylation of non-activated arenes

A visible-light-induced spirocyclizative hydroarylation via reductive dearomatization of a series of non activated arenes including 2-phenyl indoles and naphthalene derivatives under mild conditions is de scribed. An intriguing chemoselective dearomative hydroarylation of 2-phenyl indoles is presented. Th dearomative hydroarylation protocol rapidly delivers valuable spirocycles with carbon-carbon doub bonds from readily accessible aromatic precursors in a single step.     

Unusual

All-carbon 1,3-dipoles derived from allenic esters/ketones, by catalytic interaction with triphenylphosphine, undergo an unusual [8 + 2] annelation with tropone, leading to 8-oxa-9-(ethoxycarbonyl/acylalkylidene)bicyclo[5.3.0]deca-1,3,5-trienes. Dipoles derived from allenic ketones as well as an alpha-methyl-substituted allenic ester display high reactivity and selectivity.     

Ruthenium-Catalyzed Hydroarylation of Methylenecyclopropanes through CH Bond Cleavage: Scope and Mechanism

Intermolecular hydroarylation reactions of highly strained methylenecyclopropanes 2-phenylmethylenecyclopropane (1), 2,2-diphenylmethylenecyclopropane (2), methylenespiropentane (3), bicyclopropylidene (4), (dicyclopropylmethylene)cyclopropane (5), and benzhydrylidenecyclopropane (6) through C?H bond functionalization of 2-phenylpyridine (7?a) and other arenes with directing groups were studied. The reaction was very sensitive to the substitution on the methylenecyclopropanes. Although these transformations involved (cyclopropylcarbinyl)-metal intermediates, substrates 1 and 4 furnished anti-Markovnikov hydroarylation products with complete conservation of all cyclopropane rings in 11-93?% yield, whereas starting materials 3 and 5 were inert toward hydroarylation. Methylenecyclopropane 6 formed the products of formal hydroarylation reactions of the longest distal C?C bond in the methylenecyclopropane moiety in high yield, and hydrocarbon 2 afforded mixtures of hydroarylated products in low yields with a predominance of compounds that retained the cyclopropane unit. As byproducts, Diels-Alder cycloadducts and self-reorganization products were obtained in several cases from substrates 1-3 and 5. The structures of the most important new products have been unambiguously determined by X-ray diffraction analyses. On the basis of the results of hydroarylation experiments with isotopically labeled 7?a-[D(5) ], a plausible mechanistic rationale and a catalytic cycle for these unusual ruthenium-catalyzed hydroarylation reactions have been proposed. Arene-tethered ruthenium-phosphane complex 53, either isolated from the reaction mixture or independently prepared, did not show any catalytic activity.     

Synthesis of furan from allenic sulfide derivatives

In this paper, we report the synthesis of furan derivatives from allenic sulfides. By the reaction with NaH, β-Hydroxyl allenic sulfides were found to generate furan products in excellent yields with the removal of phenylthio group. β-Aldehyde allenic sulfides were found to give similar furan products with one more substituent when treated with additional nucleophilic reagents. β-ketone allenic sulfides can also cyclize to give furan derivatives with the promotion of P₂O₅.     

Ruthenium‐Catalyzed Hydroarylation of Methylenecyclopropanes through C?H Bond Cleavage: Scope and Mechanism

Intermolecular hydroarylation reactions of highly strained methylenecyclopropanes 2‐phenylmethylenecyclopropane ( 1 ), 2,2‐diphenylmethylenecyclopropane ( 2 ), methylenespiropentane ( 3 ), bicyclopropylidene ( 4 ), (dicyclopropylmethylene)cyclopropane ( 5 ), and benzhydrylidenecyclopropane ( 6 ) through C? H bond functionalization of 2‐phenylpyridine ( 7 a ) and other arenes with directing groups were studied. The reaction was very sensitive to the substitution on the methylenecyclopropanes. Although these transformations involved (cyclopropylcarbinyl)–metal intermediates, substrates 1 and 4 furnished anti‐Markovnikov hydroarylation products with complete conservation of all cyclopropane rings in 11–93 % yield, whereas starting materials 3 and 5 were inert toward hydroarylation. Methylenecyclopropane 6 formed the products of formal hydroarylation reactions of the longest distal C? C bond in the methylenecyclopropane moiety in high yield, and hydrocarbon 2 afforded mixtures of hydroarylated products in low yields with a predominance of compounds that retained the cyclopropane unit. As byproducts, Diels–Alder cycloadducts and self‐reorganization products were obtained in several cases from substrates 1 – 3 and 5 . The structures of the most important new products have been unambiguously determined by X‐ray diffraction analyses. On the basis of the results of hydroarylation experiments with isotopically labeled 7 a ‐[D₅], a plausible mechanistic rationale and a catalytic cycle for these unusual ruthenium‐catalyzed hydroarylation reactions have been proposed. Arene‐tethered ruthenium–phosphane complex 53 , either isolated from the reaction mixture or independently prepared, did not show any catalytic activity.     

A simple approach to separate a mixture of homopropargylic and allenic alcohols

A simple and practical approach to separate homopropargylic alcohol from allenic alcohol has been developed. It involves the formation of an insoluble silver acetylide species between silver nitrate and homopropargylic alcohol in aqueous acetone which can be separated from the allenic alcohol through a simple filtration. The homopropargylic alcohol can subsequently be recovered by hydrolysis with 1 N HCl. This protocol has been applied to the separation of a mixture of chiral homopropargylic and allenic alcohols in excellent yields with retention of absolute stereochemistry.     

Manganese‐Catalyzed C−H Functionalizations: Hydroarylations and Alkenylations Involving an Unexpected Heteroaryl Shift

A manganese‐catalyzed regio‐ and stereoselective hydroarylation of allenes is reported. The C−H functionalization method provides access to various alkenylated indoles in excellent yields. Moreover, a hydroarylation/cyclization cascade involving an unexpected C−N bond cleavage and aryl shift has been developed, which provides a new synthetic approach to substituted pyrroloindolones.     

Iron(III)-catalyzed hydroarylation of propiolic acid with activated arenes

FeCl₃/AgOTf-catalyzed hydroarylation of propiolic acid with electron-rich arenes such as mesitylene, tetramethylbenzene, and pentamethylbenzene in trifluoroacetic acid proceeded to give 3-arylpropenoic acids in moderate to high yields. The same reactions with anisole and 1,4-dimethoxybenzene afforded double hydroarylation products, 3,3-diarylpropionic acids.     

Proton-catalyzed hydroamination and hydroarylation reactions of anilines and alkenes: a dramatic effect of counteranions on reaction efficiency

The anilinium salt, [PhNH3][B(C6F5)4], has been identified as a catalyst for the hydroamination and hydroarylation of several different types of alkenes with anilines. The weakly coordinating counterion of this acid plays a key role in this transformation. The reaction is facile for styrenes and tolerates norbornene, cyclic alkenes, and cyclohexadiene. Selectivity between hydroamination and hydroarylation products can be tuned using reaction time, temperature, and substrate substitution. Details regarding the substrate scope and selectivity of this hydroamination/hydroarylation reaction are discussed.     

Rhodium(I)-catalyzed allenic carbocyclization reaction affording delta- and epsilon-lactams

This letter extends the scope of the rhodium(I)-catalyzed allenic Alder-ene carbocyclization reaction to the preparation of delta- and epsilon-lactams from amides. A variety of allenic propiolamides were cycloisomerized to give a number of unsaturated delta-lactams. In addition, allenic propargylamides give good yields of the corresponding epsilon-lactams. Formation of lactams possessing these ring sizes has rarely been accomplished via transition-metal-catalyzed carbon-carbon bond forming strategies. Thus, this approach provides an alternative strategy for synthesizing these substructures. [reaction: see text].