Reactions of N-substituted 2,6(3,5)-dialkyl-1,4-benzoquinone imines with arenesulfinic acids

The regioselectivity in the reactions of N-arylsulfonyl-2,6-dialkyl-1,4-benzoquinone imines with arenesulfinic acids (1,6-, 6,1-, or 6,3-addition) is determined by steric factor, while in the reactions of N-aroyl-1,4-benzoquinone imines electronic effect of substituents in the quinoid ring is crucial. The reactions of N-arylsulfonyl-3,5-dimethyl-1,4-benzoquinone imines with arenesulfinic acids follow mainly the 1,4-addition pattern. N-(N-Arylsulfonylbenzimidoyl)-1,4-benzoquinone imines are capable of reacting in a way similar to both N-arylsulfonyl and N-aroyl derivatives.     

γ-手性顺式的共轭烯醛与有机锂化合物的立体选择性反应

本文研究了在手性的顺式-γ-氨基-α,β-不饱和醛(7)与有机锂化合物的亲核加成反应中的1,4-不对称诱导效应.结果表明: 7与α-烷氧基乙烯醇锂类化合物的反应导致了优良的非对映立体选择性(d.e. : 60～90%), 而与烷基锂试剂的反应也给出了高度的立体选择性(d.e.: 74～86%). 这说明在这些反应中 , 存在着一种1,4-不对称诱导反应 .     

Synthesis of optically active,unnatural α-substituted glutamic acid derivatives by a chiral calcium-catalyzed 1,4-addition reaction

The first catalytic asymmetric 1,4-addition reactions of azlactones with acrylic esters have been developed. A chiral coordinative calcium catalyst was found to be effective for these reactions, and the desired 1,4-adducts were obtained in good yields and enantioselectivities. The product was converted to the corresponding α-alkylated glutamic acid by acid hydrolysis.     

1,4-disubstituted pyridazino[4,5-d] pyridazines

1,4-Bis(methyIthio)pyridazino[4,5-d]pyridazine (IV) was synthesized from 4,5-pyridazinedi-carboxylic acid in three steps. By employing IV as an intermediate, various 1,4-disubstituted pyridazino[4,5-d]pyridazine derivatives of classes 1,4-N,S; 1,4-N,O; 1,4-O,S; and 1,4-O,O were prepared by one-step or two-step nucleophilic substitution reactions. Steric, polar and resonance effects were observed in some of these reactions and are discussed.     

Spectroscopic and structural aspects of the reactions of 1,4-quinones with sulfur and nitrogen nucleophiles

A series of 1,4-benzoquinone derivatives from 2,5-dichloro-3,6-diethoxy-1,4-benzoquinone and 2,6-dichloro-3,5-diethoxy-1,4-benzoquinone were prepared by nucleophilic substitution reactions of sulfur and nitrogen nucleophiles. Spectral techniques (¹H NMR, ¹³C NMR, FT–IR, and LC–MS) were employed to structurally characterize the reaction products of alkoxy, chloro substituted-1,4-benzoquinones with thiols and amines in the presence of sodium carbonate in ethanol at room temperature. The orientations and the regioselectivity of the reactions of alkoxy, chloro substituted-1,4-benzoquinones with various thiol and amine nucleophiles are discussed.     

Suzuki–Miyaura reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone. Electronic and steric effects on the site-selectivity

The palladium(0)-catalyzed Suzuki cross-coupling reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone afforded various aryl-substituted thioxanthones. While the Suzuki reactions of the bis(triflate) derived from 1,3-dihydroxythioxanthone proceeded by site-selective attack in favor of position 3, the reactions of the bis(triflate) of 1,4-dihydroxythioxanthone proceeded in favor of position 1. The site-selectivity is controlled by steric and electronic parameters.     

The solar-chemical photo-Friedel-Crafts heteroacylation of 1,4-quinones

Photochemical reactions between 1,4-benzo- and 1,4-naphthoquinone and several heteroaromatic carbaldehydes were investigated under solar irradiation conditions. These reactions gave the corresponding heteroacylated hydroquinones in the range 71%-92% yield.     

CARO'S ACID SUPPORTED ON SILICA GEL. PART 7: A VERSATILE REAGENT FOR THE AROMATIZATION OF HANTZSCH 1,4-DIHYROPYRIDINES UNDER NON-AQUEOUS CONDITION AND MICROWAVE IRRADIATION

Efficient oxidation of 1,4-dihydropyridines with Caro's acid on silica gel is achieved under nonaqueous conditions and in a domestic microwave oven. The reactions under microwave irradiation were shorter in duration and higher in yields than the reactions in conventional method, confirming the potentiality of microwave heating in aromatization of Hantzsch 1,4-dihydropyridines.     

Synthetic transformations of higher terpenoids: XXVIII. Diels-Alder reactions of 16-(trimethylsiloxybutadienyl) labdanoids

15,16-Epoxy-16-(3-trimethylsiloxybuta-1,3-dien-1-yl)labdanoids were synthesized, and their reactions with cyclic dienophiles (1,4-benzoquinone, 1,4-toluquinone, 2-bromo-6-methyl-1,4-benzoquinone, and N-methylmaleimide) were studied. The reactions with unsymmetrically substituted benzoquinones were not selective. Methods for the preparation of hybrid compounds containing furan diterpenoid and substituted naphthoquinone, octahydroisoindoletrione, or hexahydroisoindoledione fragments were proposed.     

Studies on tandem ene/intramolecular diels-alder reactions

Tandem ene/intramolecular Diels-Alder reactions of 1,4-cyclohexadiene and - or -activated acetylenes are optimized. Analogous reactions with disubstituted bicyclohexa-1,4-dienes regioselectively produce highly functionalized tetracyclic adducts.     

Collective reaction behavior of an oscillating system coupled with an excitable reaction

The collective reaction behavior of limit cycles coupled to a nonoscillatory forcing is investigated experimentally and computationally. The coupled chemical system is constructed by adding 1,4-cyclohexanedione (CHD), a species which is capable of forming an oscillator with acidic bromate, into the cerium-catalyzed Belousov-Zhabotinsky reaction. Two levels of coupling exist in the system: (1) through autocatalytic reactions with bromine dioxide radicals and (2) via reactions with oxidized metal catalysts. Experiments illustrate that there is an optimum [1,4-CHD]/[cerium] ratio for inducing complex oscillations, whereas in the 1,4-CHD and malonic acid concentration phase plane two resonant ratios are observed for the onset of complex behavior. In addition, bromate, the oxidant for both suboscillators, also exhibits subtle influences on the complexity of the collective reaction behavior. The experimental observations are qualitatively reproduced with the Field-Koros-Noyes mechanism, modified to account for the coupling reactions with the 1,4-CHD-bromate system.     

New highlights in the synthesis and reactivity of 1,4-dihydropyrazine derivatives

In the course of our investigations on the synthesis of original nitrogen heterocyclic derivatives, we were interested in the synthesis and study of original 1,4-dihydropyrazine rings. To this aim the desired bisvinylphosphate derivative was prepared from N-Boc piperazine-2,5-dione and then was engaged in palladium catalyzed reactions (reduction, Suzuki and Stille cross-coupling reactions). The 1,4-dihydropyrazine and the corresponding 2,5-disubstituted derivatives were obtained in fair to good yields and were then functionalized under anionic conditions. Aromatization into 1,4-pyrazines was investigated in a second stage.     

Enantioselective addition of diethylzinc to aldehydes catalyzed by optically active 1,4-aminoalcohols

Enantioselective addition reactions of diethylzinc to aldehydes were performed by catalytic reactions with chiral 1,4-aminoalcohols. Optically active 1,4-aminoalcohols were synthesized from (+)-camphor and (−)-fenchone through four steps involving iodine-mediated lactonization of 3-hydroxy acids.     

N-Arylation of azoles with low basicity by 1,4-dimethoxybenzene during undivided electrolysis

The reactions of 1,4-dimethoxybenzene with 4-nitropyrazole, 3,4-dinitro-5-methylpyrazole, 1,2,4-triazole, 3-nitro-1,2,4-triazole, and tetrazole were studied during undivided amperostatic electrolysis on a Pt electrode in MeCN, CH₂Cl₂, and MeOH. The main reaction products were 2-azolyl-1,4-dimethoxybenzenes and (or) 1,4-diazolyl-1,4-dimethoxycyclohexa-2,5-dienes. In all cases except 1,2,4-triazole, N-arylation occurs only in the presence of the Alk₄N⁺ salts of azoles or 2,4,6-trimethylpyridine as a base. The mechanism of the reactions is discussed.     

[2 + 2] Cycloaddition Reactions of Butadienyl Ketene with 1,4‐Diazabuta‐1,3‐dienes: Synthesis of Functionalized Butadienyl‐4‐iminomethyl‐azetidin‐2‐ones and Butenylidene‐butadienyl‐[2,2′‐biazetidine]‐4,4′‐diones

The reactions of butadienylketene with variety of 1,4‐diazabuta‐1,3‐dienes are studied. The reactions resulted in the formation of previously unknown functionalized cis butadienyl‐4‐iminomethyl‐azetidin‐2‐ones and butenylidene‐butadienyl‐[2,2′‐biazetidine]‐4,4′‐ diones. Butadienyl ketene reacts in [2+2] cycloaddition fashion with both iminic portion of 1,4‐ diazabuta‐1,3‐dienes and competitive [4+2] cycloaddition reaction of 1,4‐diazabuta‐1,3‐dienes as 4π component with butadienyl ketene as 2π component are not observed.     

Facile Synthesis of 2‐Amino‐1,4‐naphthoquinones catalyzed by Molecular Iodine under Ultrasonic Irradiation

The conjugate addition reactions of amines with 1,4‐naphthoquinone were catalyzed efficiently by molecular iodine under ultrasonic irradiation to afford 2‐amino‐1,4‐naphthoquinones in moderate to excellent yields.     

The First Functionalized 6,12-Diazatetrakishomocubanes

The photodimerization of asymmetric 4-aryl-1,4-dihydropyridines results, totally unexpectedly, in the new 6,12-diazatetrakishomocubanes 1. This is in contrast to the previously observed [2+2] photocycloaddition reactions of symmetrical 4-aryl-1,4-dihydropyridines     

Palladium-catalyzed regiospecific tandem allylation of 2-aminophenols using 2-butene-1,4-diol

The direct activation of C-O bonds in 2-butene-1,4-diol by palladium complexes has been accelerated by carrying out the reactions in the presence of a titanium reagent. Palladium-catalyzed regiospecific tandem allylation of 2-aminophenols with 2-butene-1,4-diol leads to 3,4-dihydro-2-vinyl-2H-1,4-benzoxazines.     

Synthesis of novel 1,4 naphthoquinone-based molecules by an Ugi-type four-component reaction

In an attempt to further exploit multicomponent reactions in the field of 1,4 naphthoquinone-based compounds, we describe an Ugi-type multicomponent approach for the synthesis of novel 3-substituted 1,4 naphthoquinone molecules. The process relies on the execution of an enol-Ugi reaction between an enol-3-nitro-1,4 naphthoquinone with different secondary diamines and isocyanides. The novel methodology showed great chemical efficiency and versatility.     

Specific and selective reduction of aromatic nitrogen heterocycles with the bis-pyridine complexes of bis(1,4-dihydro-1-pyridyl)zinc and bis(1,4-dihydro-1-pyridyl)magnesium

Aromatic nitrogen heterocycles, e.g. quinoline, 2,2‘-bipyridyl and 1,10-phenanthroline, are reduced in a uniquely specific and selective way by the bispyridine complexes of bis(1,4-dihyro-1-pyridyl)zinc and bis(1,4-dihydro-1-pyridyl)magnesium. The reactions occur by hydrogen transfer from the metal-bound 1,4-dihydropyridyl moieties to the substrates and yield zinc or magnesium salts of the 1,4-dihydroazaaromatic derivatives. Upon hydrolysis, the 1,4-dihydroazaaromatic compounds are liberated from the metal ions. The isolation and purification of several of the (novel) reduced compounds, e.g. 1,4-dihydroquinoline and 1,4-dihydro-1,10-phenanthroline, are described.