An ab initio study of heterodienophiles addition to 2,3-diaza-1,3-butadiene: An example of endo-lone-pair effect on the reaction energy barrier

Transition states for the Diels-Alder reactions of 2,3-diaza-1,3-butadiene with ethylene, formaldehyde, formaldimine, cis- and trans- diazene, and nitrosyl hydride were located by ab initio molecular orbital calculations. The bond orders of the new forming bonds have been used to determine the asynchronicity of the reactions. Ab initio calculations show that the energy barrier for the hetero-Diels-Alder reactions is relatively high. The highest energy barrier of 34.76 kcal/mol calculated at the MP4/6-31G*//MP2/6-31G* level was found for the exo-cis-diazene addition to 2,3-diaza-1,3-butadiene. In all cases, when two diastereomeric transition structures are possible, the one with the endo hydrogen, exo lone pair was predicted to have a lower activation barrier. This behavior can be explained by the n-π and n-n loan pair repulsion interaction between the dienophile and diene heteroatoms in the corresponding transition state. The barrier is higher for those reactions which in the transition state have more lone electron pairs. Also, the barrier is higher when the lone pairs are endo oriented than when they are exo oriented in the transition state. © 1996 by John Wiley & Sons, Inc.     

Chemistry of o-Benzoquinones and Masked o Benzoquinones VII.: Regioselective and Stereoselective Cycloadditions of 6, 7-Dipropyl- and 8, 9-Eipropyl-1, 4-Dioxaspiro[4.5] deca-6, 8-Di-En-2, 10-Dione with Monosubstituted Ethylenes

The cycloadditions of the titled two masked o-benzoquinones, 2 and 3 , with monosubstituted ethylenes including ethyl acrylate, styrene, ethyl vinyl ether and 1-hexene were studied. The reactions proceeded with high stereoselectivity and regioselectivity to give endo head-to-head adducts when ethyl acrylate, styrene and ethyl vinyl ether were used as addenda. In the case of 1-hexene, the reaction with 2 took place with high regioselectivity but low stereoselectivity to afford endo as well as exo head-to-head adducts while the reaction with 3 occurred with less regioselectivity to produce presumably all the eight possible isomers. The regiochemistry of the adducts were determined by the ¹H nmr analysis of their hydrolysis products, bicyclo[2,2,2]oct-5-en-2,3-diones 6 , and the subsequent photolysis products, 1,3-cyclohexadienes 7 . The stereochemistry was established by the study of the lanthanide induced shifts of compounds 6a-6f with Fu(fod)₃. The regioselectivity and stereoselectivity of these cycloaddition reactions were explained in terms of frontier molecular orbital theory and steric effect. The present study provides also a facile method to prepare regioselectively bicyclo[2, 2, 2]oct-5-en-2,3-diones (stereo-selectively also) and 1,3-cyclohexadienes from unsymmetric catechols via masked o-benzoquinones.     

Structure of tetrahydropyridazines formed from 1-isopropyl-3,4-dimethyl-1,2-diaza-1,3-butadiene and methyl vinyl ketone

In contrast to the cis isomer, trans-1-isopropyl-3,4-dimethyl-1,2-diaza-1,3-butadiene reacts with methyl vinyl ketone to give a mixture of cis and trans isomers of 5-and 6-acetyl-1-isopropyl-3, 4-dimethyl-²-tetrahydropyridazines. The preponderance of the cis isomer in the case of 5-substituted tetrahydropyridazines constitutes evidence for the existence of secondary orbital interactions of the acetyl group of the dienophile with the C=C bond of the diene component.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1684–1686, December, 1978.     

A convenient synthesis of pyridazine-3,4-dicarboxylic acid by a hetero diels-alder reaction

A convenient route to prepare unsubstituted pyridazine-3,4-dicarboxylic acid on a preparative scale is described. The synthesis involves a hetero Diels-Alder reaction between a new 1,2-diaza-1,3-diene and ethyl vinyl ether and oxidation of the intermediate 1,4,5,6-tetrahydropyridazine as the key step.     

1,3-Dipolar cycloaddition approach to pyrrolidine analogues of C-nucleosides related to pseudouridine

Pyrrolidine analogues of C-nucleosides related to pseudouridine have been synthesized by 1,3-dipolar cycloaddition reactions of uracil-5 and 2,4-dimethoxypyrimidine-5 nitrones with allyl alcohol and methyl acrylate, and subsequent reductive cleavage of the isoxazolidine cycloadducts. The dimethoxy derivatives have been easily deprotected to the corresponding uracils bearing the pyrrolidine ring instead of a sugar moiety. The regio and stereoselectivity of the reactions are discussed.     

A novel approach to the pyrido[4,3-c]pyridazine ring. Synthesis of pyrido[4,3-c]pyridazin-5(6H)-one from 3,4-disubstituted pyridazines

The synthesis of new pyrido[4,3-c]pyridazin-5(6H)-one from ethyl 3-methyl-4-pyridazinecarboxylate using an enamination/ring closure sequence is described. The starting material is easily available from a hetero Diels-Alder reaction between a 1,2-diaza-1,3-diene and ethyl vinyl ether and oxidation of the resulting 1,4,5,6-tetrahydropyridazine.     

Preparation of 1,3-dienyl organotrifluoroborates and their Diels-Alder/cross-coupling reactions

2-BF₃-substituted 1,3-butadienes with potassium and tetrabutyl ammonium counterions have been prepared in gram quantities from chloroprene via a simple synthetic procedure. The potassium salt of this new main group element substituted diene has been characterized by ¹H, ¹³C, ¹¹B, and ¹⁹F NMR and the tetra n-butyl ammonium salt was also characterized by X-ray crystallography. Diels-Alder reactions of these dienes with dienophiles such as ethyl acrylate, methyl vinyl ketone, and N-phenylmaleimide are reported as well as subsequent Pd-catalyzed cross-coupling reactions of those Diels-Alder adducts. 4-Phenyl-2-BF₃-substituted 1,3-diene was prepared by magnesium-halogen exchange from the corresponding 2-bromo and iodo dienes. The 4-phenyl-2-bromo-1,3-butadiene was also characterized by X-ray crystallography. 4-Phenyl-2-BF₃-1,3-butadiene was used in Diels-Alder/cross-coupling reactions and the product of a Diels-Alder reaction with N-phenylmaleimide followed by cross-coupling with 4-bromo-benzonitrile was also characterized by X-ray crystallography.     

C59XH（X=N,B）与1,3-丁二烯Diels-Alder环加成反应的区域选择性

应用半经验的AMI和密度泛函B3LYP/6-31G*方法对1,3-丁二烯与C59XH(X=N,B)Diels-Alder环加成反应的区域选择性进行理论研究,选择一些有代表性的C59XH(X=N,B)的6-16键探讨环加成反应的机理.1,3-丁二烯与C59NH进行的Diels-Alder反应,随着加成位置远离C59NH的N原子,活化能越来越低,但都比1,3-丁二烯与C60相应反应的活化能高.与此相反,对于1,3-丁二烯与C59BH进行的环加成反应.加成位置最靠近B原子的2,12/r-和2,12/f-过渡态的势垒最低,并且比1,3-丁二烯与C60进行环加成反应的活化能约低18 kJ·mol-1,其产物也是热力学最稳定的.与C60相应的反应相比,C59NH和C59BH中N和B原子不同的电子性质对其邻位双键进行Diels-Alder环加成反应的活性产生了不同影响,前者使反应活性降低,后者使反应活性增强.     

1-三氯锡烷基-2,3-丁二烯和2-三氯锡烷基-1,3-丁二烯与甲醛反应的B3LYP研究

用密度泛函方法在B3LYP/6-31G^**水平上研究了1-三氯锡烷基-2,3-丁二烯和2-三氯锡烷基-1,3-丁二烯与甲醛的反应.优化得到各驻点的几何构型,通过振动分析和内禀反应坐标对过渡态进行了确认,解析了反应路径.并用SCRF(PCM)方法在同一水平上对在CH₂Cl₂溶液中的两反应进行了研究.计算了两反应在气相和CH₂Cl₂溶液中的活化能垒、自由能和平衡常数.结果表明,反应具有很强的选择性,主要得到1-三氯锡烷基-2,3-丁二烯与甲醛反应的产物.该结果与实验事实一致.     

Comparison of catalytic properties of systems based on nickel complexes with 1,4-diaza-1,3-butadiene ligands in reactions of styrene hydrogenation and ethylene polymerization

Turnover frequencies of catalytic systems based on nickel complexes with 1,4-diaza-1,3-butadiene (α-diimine) ligands in the reactions of styrene hydrogenation and ethylene polymerization were determined. Results are presented of a study by the electron paramagnetic resonance method and IR spectroscopy of 1,4-diaza-1,3-butadiene complexes of nickel(II) and anion radicals formed in the interaction of the starting components under the conditions of catalysis. It was shown that the paramagnetic Ni(I) complexes are precursors of complexes catalytically active in the hydrogenation and polymerization reactions.     

Cationic polymerization of dimethyl-1,3-butadienes

The cationic polymerizations of dimethyl-1,3-butadienes with various catalysts in methylene chloride and toluene have been investigated. The activity of catalysts decreased in the order WCl₆ > AcClO₄ > SnCl₄·TCA > BF₃OEt₂. The homopolymerization rate of dimethyl-1,3-butadienes with WCl₆, AcClO₄, and SnCl₄·TCA decreased in the order 1,3-dimethyl-1,3-butadiene > 2,3-dimethyl-1,3-butadiene > 1,2-dimethyl-1,3-butadiene > 2,4-hexadiene. The polymers prepared with WCl₆, SnCl₄.TCA, and BF₃OEt₂ were rubberlike polymers or white powders, whereas those prepared with AcClO₄ were oily oligomers. The 1,4-propagation increased in the order 1,2-dimethyl-1,3-butadiene < 1,3-dimethyl-1,3-butadiene < 2,3-dimethyl-1,3-butadiene < 2,4-hexadiene. This order may indicate that the steric effect of methyl group determine primarily the microstructure of the polymer. The relative reactivity of dimethyl-1,3-butadienes toward a styryl cation decreased in the order 1,3-dimethyl-1,3-butadiene > 1,2-dimethyl-1,3-butadiene > 2,3-dimethyl-1,3-butadiene > 2,4-hexadiene. This order may be explained in terms of the stability of the resulting allylic cation.     

Access to new 2-oxofuro[2,3-b]pyrroles and 2-methylenepyrroles through the reaction of 1,2-diaza-1,3-butadienes and gamma-ketoesters

New and interesting 2-oxofuro[2,3-b]pyrroles and 19-methyl-15-oxa-20-azatricyclo[12.3.3.0(1,14)]icos-18-en-18-carboxylates have been obtained in good yields by the one-pot reaction, in basic medium, of 1,2-diaza-1,3-butadienes with diethyl or dimethyl acetylsuccinate or methyl 2-(1,3-dioxo-2-cyclotetradecyl)acetate, respectively, under mild conditions. Treatment of the same starting materials with diethyl 2-acetylglutarate, in acidic medium, afforded unknown 2-methylenepyrrole derivatives in high yields. Novel 4-(3-oxopropyl)-2,5-dimethyl-1H-pyrrole-3-carboxylates also have been achieved by reacting 1,2-diaza-1,3-butadienes with ethyl or methyl 4-acetyl-5-oxo-hexanoate.     

The Diels-Alder Reaction of Dienes Derived from Substituted 3-(Phenyl-Thio)-3-Sulfolenes

Substituted 3-(phenylthio)-3-sulfolenes (3) and (4) are good precursors for 2-(phenylthio)-1,3-butadienes (5) and (6). The Diels-Alder reaction of the dienes derived from (3) and (4) with various dienophiles was studied. It was found that heating of sulfolenes (3) with methyl propiolate and N-phenylmaleimide afforded the Diels-Alder adducts of (5) directly and with complete regio- and stereospecificity. The same reaction with methyl vinyl ketone gave a mixture of endo and exo addition products. If sulfolenes (3) were first converted to the dienes (5) using lithium aluminum hydride and then reacted with methyl vinyl ketone in the presence of anhydrous zinc chloride, the stereoselectivity could be improved. Sulfolenes (4) also underwent cycloreversion/cycloaddition with methyl acrylate, methyl vinyl ketone, and N-phenylmaleimide, but gave mostly the double bond-isomerized cycloaddition products. The regiochemistry of cycloaddition was delicately dependent on the dienophiles used.     

C59XH(X=N,B)与1,3-丁二烯Diels-Alder环加成反应的区域选择性

应用半经验的AM1和密度泛函B3LYP/6-31G*方法对1,3-丁二烯与C59XH(X=N, B) Diels-Alder环加成反应的区域选择性进行理论研究, 选择一些有代表性的C59XH(X=N, B)的6—6键探讨环加成反应的机理. 1,3-丁二烯与C59NH进行的Diels-Alder反应, 随着加成位置远离C59NH的N原子, 活化能越来越低, 但都比1,3-丁二烯与C60相应反应的活化能高. 与此相反, 对于1,3-丁二烯与C59BH进行的环加成反应, 加成位置最靠近B原子的2,12/r-和2,12/f-过渡态的势垒最低, 并且比1,3-丁二烯与C60进行环加成反应的活化能约低18 kJ·mol-1, 其产物也是热力学最稳定的. 与C60相应的反应相比, C59NH和C59BH中N和B原子不同的电子性质对其邻位双键进行Diels-Alder环加成反应的活性产生了不同影响, 前者使反应活性降低, 后者使反应活性增强.     

Sulfur ylides. 12. Optically active keto stabilized sulfur ylide obtained from L-proline: synthesis and study

Optically active keto stabilized sulfur ylide was synthesized from L-proline. The reactions of the ylide with methyl acrylate and methyl vinyl ketone afforded 1,2-disubstituted cyclopropanes. In the case of acrylonitrile, a mixture of 1,2- and 1,1-disubstituted cyclopropanes was obtained. Acylation of the ylide with acetic anhydride gave twice stabilized sulfur ylide.     

Straightforward entry into 5-hydroxy-1-aminopyrrolines and the corresponding pyrroles from 1,2-diaza-1,3-butadienes

The synthesis of 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and 5-unsubstituted-1-aminopyrrole-3-carboxylic acid derivatives from 1,2-diaza-1,3-butadienes and aldehydes is presented. These domino reactions offer the advantage of executing multistep transformation without intermediate workup procedures. The stereoselectivity of ring closure to 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and phenyl transposition to 2,3-diphenyl-1-aminopyrrole-3-carboxylic acid derivatives are also studied.     

Efficient synthesis and environmentally friendly reactions of PEG-supported 1,2-diaza-1,3-butadiene

[reaction: see text] Here, we report the protocol for the preparation of new poly(ethylene glycol)-supported 1,2-diaza-1,3-butadiene. In addition, we discuss an application of this supported reagent in an efficient and environmentally friendly one-pot synthesis of 2-thiazol-4-one derivatives by reaction with thioamides.     

Regio- and stereoselectivity in the Diels–Alder reaction of vinylallenes with acrolein: an ab initio study

To explore the regio- and stereoselectivity in Diels–Alder reactions of vinylallenes with acrolein, a parent vinylallene/acrolein system and a methyl-substituted vinylallene/acrolein system were studied. Ab initio calculations were used to identify eight transition state structures for each of the two Diels–Alder reactions at various computational levels (RHF/6-31G(d), RHF/6-311G(2d), B3LYP/6-311G(2d), and MP2/6-311G(2d)). The relative energies of the endo and exo transition states along with the regioselectivity have been determined from these calculations. In the parent vinylallene/acrolein system, the endo s-cis transition structure is the preferred stereoselectivity at all levels of theory, however, there is no regioselectivity. In the methyl substituted vinylallene/acrolein system, the endo s-trans transition state tends to compete with the endo s-cis transition state at the RHF levels of theory and is 1 kcal/mol more stable at the B3LYP/6-311G(2d) level of theory. Also, in the methyl-substituted system, there is now a definite preference for one regioisomer over the other. Both Diels–Alder reaction systems are asynchronous with the methyl-substituted system being more pronounced.     

Binaphthol-derived bisphosphoric acids serve as efficient organocatalysts for highly enantioselective 1,3-dipolar cycloaddition of azomethine ylides to electron-deficient olefins

A variety of chiral bisphosphoric acids derived from binaphthols have been evaluated for enantioselective 1,3-dipolar cycloaddition reactions, revealing that the feature of the linker in the catalysts exerted great impact on the stereoselectivity. Among them, the oxygen-linked bisphosphoric acid 1a provided the highest level of stereoselectivity for the 1,3-dipolar cycloaddition reaction tolerating a wide range of substrates including azomethine ylides, generated in situ from a broad scope of aldehydes and α-amino esters, and various electron-deficient dipolarophiles such as maleates, fumarates, vinyl ketones, and esters. This reaction actually represents one of the most enantioselective catalytic approaches to access structurally diverse pyrrolidines with excellent optical purity. Theoretical calculations with DFT method on the formation of azomethine ylides and on the transition states of the 1,3-dipolar cycloaddition step showed that the dipole and dipolarophile were simultaneously activated by the bifunctional chiral bisphosphoric acids through the formation of hydrogen bonds. The effect of the bisphosphoric acids on reactivity and stereochemistry of the three-component 1,3-dipolar cycloaddition reaction was also theoretically rationalized. The bisphosphoric acid catalyst 1a may take on a half-moon shape with the two phosphoric acid groups forming two intramolecular hydrogen bonds. In the case of maleates, one phosphate acts as a base to activate the 1,3-dipole, and simultaneously, the two hydroxyl groups in the catalyst 1a may respectively form two hydrogen bonds with the two ester groups of maleate to make it more electronically deficient as a much stronger dipolarophile to participate in a concerted 1,3-dipolar cycloaddition with azomethine ylide. However, in the cases involving acrylate and fumarate dipolarophiles, only one hydroxyl group forms a hydrogen bond with the ester functional group to lower the LUMO of the C-C double bond and another one is remained to adjust the acidity and basicity of two phosphoric acids to activate the dipole and dipolarophile more effectively.     

Initiation mechanisms in copolymerization: Reaction of t-butoxyl radicals with co-monomers ethyl vinyl ether and methyl methacrylate

The radical trapping technique employing 1,1,3,3-tetramethyl-1,3-dihydro-1H-isoindol-2-yloxyl as a scavenger has been used to investigate the reaction of t-butoxyl radicals with mixtures of ethyl vinyl ether and methyl methacrylate. The range of identified products includes those from both addition and hydrogen abstraction with both monomers, head addition with ethyl vinyl ether, and some second monomer addition products. Relative rate constants have been obtained for various pairs of constituent reactions. t-Butoxyl radicals add to ethyl vinyl ether one to two times faster than to methyl methacrylate, depending on which monomer is in excess. The ratio is less than 1 in nonolefinic solvents and as high as 6 in t-butanol. This solvent effect is thought to be due to the radicals complexing to either methyl methacrylate or t-butanol (H-bonding), thereby increasing its electrophilic character. © 1997 John Wiley & Sons, Inc.