Understanding sulfone behavior in palladium-catalyzed domino reactions with aryl iodides

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions takes place mainly by means of a four-component domino process, involving one unit of the alkene and three units of the aryl iodide, affording substituted 9-phenylsulfonyl-9,10-dihydrophenanthrenes. We report here the results of a computational study on the mechanism of this domino arylation reaction. Based on these results we can explain why vinyl sulfones, unlike other electron-deficient alkenes such as enones, preferentially follow this domino pathway instead of the usual Heck pathway. The key step is a C-H activation process in which a five-membered palladacycle is formed. The greater ability of vinyl sulfones, relative to enones, to reach the transition state that leads to the formation of the initial palladacycle makes the difference.     

2-Isoxazoline derivatives. Part I. A base-promoted fragmentation of 2-isoxazolines

The action of bases on 3-aryl (or alkyl)-5-acyl-2-isoxazolines has been shown to give rise to the corresponding aromatic (or aliphatic) nitriles and α-diketones by cleavage of the O-N and C₃? C₄ bonds of the heterocyclic ring. This fragmentation reaction has been extended to other 2-isoxazolines substituted in the 5-position with electron-attracting groups.     

A new and efficient approach to isoxazolines. First synthesis of 3-aryl-5-dichloromethyl-2-isoxazolines

An efficient synthetic method for 3-aryl-5-dichloromethyl-2-isoxazolines has been established. Reactions between anhydrous chloral and acetophenones in hot acetic acid lead to 1-aryl-4,4,4-trichloro-3-hydroxybutan-1-ones (chloralacetophenones), which provided 1-aryl-4,4-dichlorobut-3-en-1-ones (2,2-dichlorovinylacetophenones) by dehydration and subsequent electrochemical reduction. These β,γ-unsaturated enones reacted with hydroxylamine yielding oxime intermediates whose treatment with aqueous sodium hydroxide gave novel 3-aryl-5-dichloromethyl-2-isoxazolines in fair to high yields. The molecular structure of a member of this family of compounds, 5-dichoromethy1-3-(4-methoxyphenyl)-2-isoxazoline, was determined by X-ray crystallography.     

Enzyme-catalyzed asymmetric domino aza-Michael/aldol reaction for the synthesis of 1,2-dihydroquinolines using pepsin from porcine gastric mucosa

An unprecedented enzyme-catalyzed asymmetric domino aza-Michael/aldol reaction of 2-aminobenzaldehyde and a,b-unsaturated aldehydes is achieved. Pepsin from porcine gastric mucosa provided mild and efficient access to diverse substituted 1,2-dihydroquinolines in yields of 38%–97% with 6%–24%enantiomeric excess(ee). This work not only provides a novel method for the synthesis of dihydroquinoline derivatives, but also promotes the development of enzyme catalytic promiscuity.     

A novel asymmetric organocatalytic Michael–aldol–dehydration domino reaction for the construction of spirocyclic benzofuranones

Organocatalytic Michael–aldol–dehydration domino reaction of 3-(1-hydroxyethylidene)benzofuran-2(3H)-ones and enones catalyzed by Cinchona-based primary amine has been developed. The desired chiral spirocyclic benzofuranones were obtained in excellent stereoselectivities (dr>20:1 and up to 96% ee) and moderate to excellent yields (up to 98%).     

The Preparation Of 2-[4,5-Dihydro-3-Aryl-5-Isoxazolyl]-Phenols From C(α),O-Dilithiooximes and Lithiated Hydroxyaryl Aldehydes

C(a), O-Oximes were dilithiated in excess lithium diisopropylamide, and the resulting intermediates were condensed with lithiated hydroxyphenyl aldehydes and related materials and cyclized with acid to afford 2-[4,5-dihydro-3-aryl-5-isoxazolyl]phenols, substituted 4,5-dihydroisoxazoles (2-isoxazolines).     

Asymmetric [5+3] Formal Cycloadditions with Cyclic Enones through Cascade Dienamine–Dienamine Catalysis

A few aminocatalytic modes, such as iminium ions and different dienamines, have provided versatile tools for the functionalization of cyclic enones at various sites. Described here is a previously unreported cascade dienamine/dienamine catalytic pathway for β‐substituted 2‐cyclopentenones, and even 2‐cyclohexenone. It involves domino α′‐regioselective Michael addition and a γ‐regioselective Mannich reaction with 3‐vinyl‐1,2‐benzoisothiazole‐1,1‐dioxides to give fused or bridged architectures, which incorporate a spirocyclic skeleton, in excellent stereocontrol, thus furnishing unusual [5+3] formal cycloaddition reactions. Moreover, preliminary biological assays showed that some of the chiral products exhibited promising activity against some cancer cell lines, thus indicating that such skeletons might serve as leads in drug discovery.     

1,3-Dipolar cycloaddition of nitrile oxides to N-vinylcarbazole: Regioselective formation of 5-(9-carbazolyl)-Δ2-isoxazolines

Aryl substituted nitrile oxides undergo 3 + 2 cycloaddition to N-vinyl carbazole to afford only one regioisomer, i.e., 3-aryl substituted 5-(9-carbazolyl)-Δ²-isoxazolines III in good yield.     

New aspects in the hydrogenolytic opening of 2-isoxazolines

It has been observed that the hydrogenolytic opening of 2-isoxazolines depends on the substituents present in positions 3 and 5. The hydrogenolysis on 10% Pd/C of 2-isoxazolines, substituted in position 3 with carbonyl or car☐yl groups and in position 5 with an aromatic group, gives oximes, in contrast to other isoxazoline derivatives. From the 5-aryl-2-isoxazolines it is possible to obtain aminoalcohols in ethanol and oximes in acetic acid.     

One-pot beta-substitution of enones with alkyl groups to beta-alkyl enones

Vinylic hydrogens at the beta-position of enones were effectively substituted with alkyl groups in a one-pot procedure to afford beta-alkyl enones in good to high isolated yields by conjugate addition of higher-order dialkyl cyanocuprates to enones, followed by a reaction with N-tert-butylbenzenesulfinimidoyl chloride at -78 degree C.     

Ni-catalyzed, ZnCl(2)-assisted domino coupling of enones, alkynes, and alkenes

A Ni(0)/ZnCl(2) system effectively promotes the coupling of enones and alkene-tethered alkynes. In the reaction with 1,6-enynes, the oxidative cyclization of Ni(0) species on enones across the alkyne part followed by ZnCl(2)-promoted cleavage generates alkenylnickel intermediates. Subsequent migratory insertion of the tethered alkene occurs with 5-exo-cyclization. When the resulting sigma-alkylnickel intermediates have beta-hydrogen atoms, the reaction terminates by beta-hydrogen elimination to provide cyclopentane derivatives. On the other hand, a sigma-alkylnickel intermediate that does not have beta-hydrogen atoms undergoes the insertion of a second alkene unit to cause a domino effect via a three-fold C-C bond formation process with and without the cleavage of one C-C bond.     

Studies on K2CO3-catalyzed 1,4-addition of 1,2-allenic ketones with diethyl malonate: controlled selective synthesis of beta,gamma-unsaturated enones and alpha-pyrones

The K2CO3 (10 mol %)-catalyzed 1,4-addition reaction of diethyl malonate with various substituted 1,2-allenic ketones leading to polyfunctionalized beta,gamma-unsaturated enones 3 or 4 was studied. With 3-unsubstituted 1-substituted-1,2-allenyl ketones, the highly selective formation of beta,gamma-unsaturated enones 4 was observed; with 1,2-allenyl ketones bearing one or two 3-substituents in the allenyl group, only beta,gamma-unsaturated enones 3 with an unmigrated carbon-carbon double bond were produced; with 3-monosubstituted-1,2-allenyl ketones Z-beta,gamma-unsaturated enones 3 were formed with excellent stereoselectivity (E:Z > 96:4); with propadienyl ketones, mixtures of beta,gamma-unsaturated enones 3 and 4 were formed. alpha-Pyrone derivatives were synthesized via the K(2)CO(3)-catalyzed or -promoted reaction of 1,2-allenic ketones with diethyl malonate via a sequential Michael addition-carbon-carbon double bond migration-lactonization process.     

Reactions of 3,3-dialkyl-2,3-dihydro-6-trifluoromethyl-4-pyrones with hydroxylamine. Synthesis and structures of 5-(1,1-dialkyl-2-hydroxyethyl)-5-hydroxy-3-trifluoromethyl-Δ2-isoxazolines

The reactions of 3,3-dialkyl-2,3-dihydro-6-trifluoromethyl-4-pyrones with hydroxylamine hydrochloride afforded regioisomeric 3(5)-(1,1-dialkyl-2-hydroxyethyl)-5-hydroxy-5(3)-trifluoromethyl-Δ²-isoxazolines depending on the reaction conditions. The title compounds were also prepared from 2,2-dialkyl-5-amino-1-hydroxy-6,6,6-trifluorohex-4-en-3-ones. The above dihydropyrones reacted with hydroxylamine (base) to yield 3-(1,1-dialkyl-2-hydroxyethyl)-5-hydroxy-5-trifluoromethyl-Δ²-isoxazolines. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1334–1339, July, 1999.     

2-Isoxazolines with an electron-acceptor substituent at C<Subscript>(5)</Subscript> in reactions with nucleophilic reagents

Depending on the substituent at position 5 of the heterocycle, reaction of 2-isoxazolines with K-selectride, molybdenum hexacarbonyl, dimsyl sodium, and butyl lithium gave 1,3-cyclo-decomposition, aromatization of the isoxazoline ring, or reduction of the functional groups in the substituted isoxazolines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.3, 447–455, March, 2007.     

Discovery of cationic domino reaction under the NMR experiment conditions: diastereoselective dimerization of 2-arylmethylideneindolin-3-ones to pentacyclic 3-hydroxyindolenine system

NMR spectroscopy (1D and 2D) showed that the protonation of the capto-dative heterocyclic α-amino enones, viz., (Z)-2-arylmethylideneindolin-3-ones, with strong acids led to stable (aryl)(3-hydroxyindol-2-yl)methyl cations. These substrates in trifluoroacetic acid underwent cationic domino reaction, which resulted in polynuclear pyrido[1,2-a: 5,6-b′]-[1,2′]biindoles.     

Microwave assisted copper-free Sonogashira coupling/5-exo-dig cycloisomerization domino reaction: access to 3-(phenylmethylene)isoindolin-1-ones and related heterocycles

An efficient microwave assisted one-pot synthesis of substituted 3-(phenylmethylene)isoindolin-1-ones is reported via a copper-free Sonogashira coupling and a regioselective 5-exo-dig cycloisomerization. This domino reaction was also extended to other related heterocycles.     

Coupling-isomerization-Claisen sequences - mechanistic dichotomies in hetero domino reactions

A new coupling-isomerization-Claisen domino reaction starting from electron deficient halides and 1-(hetero)aryl propargyl trityl ethers dichotomizes in the concluding steps of the sequence and gives rise to the formation of tricyclo[3.2.1.0(2,7)]oct-3-enes, enones, 1H-isochromenes, or indans as a consequence of minute differences of substituent effects.     

烯基取代的甲酸态四氢叶酸辅酶模型的合成及其碳单元转移反应

以邻苯二胺和乙酸为原料,经3步反应合成了8种烃基乙烯基取代的苯并咪唑盐,其结构用元素分析,¹HNMR,IR,MS和UV-Vis进行了表征,并以其作为取代的甲酸态四氢叶酸辅酶模型,同亲核试剂(格氏试剂)反应得到烃基乙烯基取代的一碳单元完全转移的产物α,β-不饱和酮,为α,β-不饱和酮的合成提供了一种简便的仿生合成新方法.     

1,2,3-三取代贫电子环丙烷衍生物与甲醇反应的研究

环丙基的化学性质类似于烯键,亲电试剂对环丙基的反应已研究得较多［１－４］．由于带多个吸电子官能基的环丙烷衍生物的合成较为困难,因此,有关亲核试剂对环丙基的反应报道较少．作者通过肿叶立德 １与米氏酸衍生物 ２的反应,简便地合成了一系列 １,２,３一三取代贫电子环丙烷衍生物３［５,６］．并用此方法高立体选择性地合成了一系列二氢呋喃衍生物［７］及γ－丁酸内酯衍生物［８］等．为弄清亲核试剂对贫电子环丙烷衍生物的反应情况,作者对亲核试剂与环丙烷类衍生物化合物３的反应作了研究．本文报道顺－１－苯甲酰基－２－对…     

Baylis-Hillman Reaction Involving Substituted Cyclic Enones in Aqueous Media

β-Substituted enones have been considered less reactive in Baylis-Hillman reaction. The reaction of cyclicenones is sluggish or does not occur at all under traditional conditions. [1] Therefore, substituted cyclic enones havebeen less explored in Baylis-Hillman reaction due to the extremely low reactivity. In this communication, we reported Baylis-Hillman reaction of substituted cyclic enones using our previously developed conditions with imidazole as catalyst. The reaction proceeded smoothly in aqueous media affording the desired product with good yields and moderate diastereoselectivity.