Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels–Alder reactions with dimethyl acetylenedicarboxylate

1989 ◽  
Vol 67 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Peter Yates ◽  
Anabela Gomes ◽  
D. Jean Burnell ◽  
Dong Dao Cong ◽  
Jeffery F. Sawyer
Keyword(s):  
Spectroscopic Method ◽  
Diels Alder ◽  
The Other ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
Product Ratio ◽  
X Ray Crystallography ◽  
Facial Selectivity ◽  
Chemical Correlation ◽  
The Individual

6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that the endo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed. Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.

Synthesis and crystal structures of three novel benzimidazole/benzoindolizine hybrids

2016 ◽  
Vol 71 (3) ◽  
pp. 231-239 ◽  
Author(s):  
Roumaissa Belguedj ◽  
Sofiane Bouacida ◽  
Hocine Merazig ◽  
Ali Belfaitah ◽  
Aissa Chibani ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Crystal Structures ◽  
Dipolar Cycloaddition ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
X Ray Crystallography ◽  
Dimethyl Maleate

AbstractThree benzoindolizine derivatives, 1, 2, and 3, were obtained via 1,3-dipolar cycloaddition. The reaction of 1-(2′-benzimidazolylmethyl)isoquinolinium ylides with dimethyl acetylenedicarboxylate gave a mixture of pyrrolo[2,1-a]isoquinoline-1,2-dicarboxylate (1) and 1,10b-dihydropyrrolo[2,1-a]isoquinoline-1,2-dicarboxylate (2) derivatives containing a benzimidazole moiety. The reaction of this isoquinolinium N-ylide with dimethyl maleate gave an unexpected 2,3-dihydropyrrolo[2,1-a]isoquinoline-1,2-dicarboxylate (3). The structures of all reported compounds have been examined by X-ray crystallography, mass spectrometry, and NMR spectroscopy.

Einfache Synthese von 2,2-Diethoxy-2,5-dihydrofuranen, 2(5 H)Furanonen und 2-Ethoxy-furanen.Kristall-und Molekülstruktur eines Barrelenon Diels-Aider Produktes [1] / Convenient Synthesis of 2,2-Diethoxy-2,5-dihydrofurans, 2(5 H)Furanones and 2-Ethoxyfurans.Crystal and Molecular Structure of a Barrelenone Diels-Alder Product [1]

1994 ◽  
Vol 49 (3) ◽  
pp. 389-406 ◽  
Author(s):  
Rolf W. Saalfrank ◽  
Wieland Hafner ◽  
Joachim Markmann ◽  
Andreas Welch ◽  
Karl Peters ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Maleic Anhydride ◽  
Structure Analysis ◽  
Diels Alder ◽  
Dimethyl Acetylenedicarboxylate ◽  
Reaction Conditions ◽  
X Ray ◽  
Convenient Synthesis

AbstractReaction of 1,2-hydroxyketones 5 with (2,2-diethoxyvinylidene)triphenylphosphorane (2) or (2,2-diethoxyvinyl)triphenylphosphonium tetrafluoroborates 6 yields the 2,2-diethoxy- 2.5-dihydrofurans 9. Depending on the reaction conditions used, the orthoesters 9 can be hydrolized to give 2(5 H)furanones 10 and 2-ethoxyfurans 11, respectively. 4,5-Dimethyl- 5.6-dihydro-2-pyranone (20) and 8-methoxycoumarin (23) are prepared, starting from (2,2-diethoxyvinyl)triphenylphosphonium tetrafluoroborate (6 a) and 1-hydroxy-2-methyl- 3-butanone (16) or 2-hydroxy-3-methoxy-benzaldehyde (21). The 2-ethoxyfuranes 11 readily undergo Diels-Alder reactions with 2-chloracrylonitrile (24), maleic anhydride (26), N-phenyl-1,2,4-triazoline-3,5-dione (28) and dimethyl acetylenedicarboxylate (30) to give the corresponding Diels-Alder products 25, 27, 29 and 31, respectively. Contrary to 2-ethoxyfuran 11b , 11a reacts with two equivalents of acetylene 30, to yield barrelenone 34. The structure of 34 unequivocally is established by X-ray structure analysis.

The reaction of steroid 2,4-dienes with acetylenes

1976 ◽  
Vol 54 (22) ◽  
pp. 3508-3516 ◽  
Author(s):  
Peter Yates ◽  
Françoise M. Walliser
Keyword(s):  
Diels Alder ◽  
The Other ◽  
Dimethyl Acetylenedicarboxylate ◽  
Methyl Propiolate ◽  
Lower Temperature

Reaction of 2,4-cholestadiene, 2,4-androstadien-17-one, or 3-trimethylsiloxy-2,4-cholestadiene with dimethyl acetylenedicarboxylate or methyl propiolate in boiling xylene results in the cleavage of rings A and B and the formation of 4-(2-arylethyl)-5-isopropenyl-7a-methyltetrahydroindane derivatives. They are considered to be formed via Diels–Alder addition of the acetylene to the steroid diene followed by a retro-Diels–Alder cleavage of the resulting bicyclo[2.2.2]octadiene system. Attempts to isolate the Diels–Alder adducts by carrying out the additions at lower temperature were unsuccessful, since no reaction occurred. However, when 2,4-androstadien-17-one was treated with dicyanoacetylene in boiling benzene, it was possible to isolate a mixture of two stereoisomeric Diels–Alder adducts containing the bicyclo[2.2.2]octadiene system in ring A; this was converted in boiling xylene to a retro-Diels–Alder product analogous to the products obtained with the other acetylenic dienophiles.

scholarly journals Spc110 N-Terminal Domains Act Independently to Mediate Stable γ-Tubulin Small Complex Binding and γ-Tubulin Ring Complex Assembly

2018 ◽  
Author(s):  
Andrew Lyon ◽  
Alex Zelter ◽  
Shruthi Viswanath ◽  
Alison Maxwell ◽  
Richard Johnson ◽  
...  
Keyword(s):  
Structural Model ◽  
Coiled Coil ◽  
The Other ◽  
Assembly Process ◽  
X Ray ◽  
X Ray Crystallography ◽  
Small Complex ◽  
Ring Complex ◽  
Biochemical Analyses

AbstractMicrotubule (MT) nucleation in vivo is regulated by the γ-tubulin ring complex (γTuRC), an approximately 2-megadalton complex conserved from yeast to humans. In Saccharomyces cerevisiae, γTuRC assembly is a key point of regulation over the MT cytoskeleton. Budding yeast γTuRC is composed of seven γ-tubulin small complex (γTuSC) subassemblies which associate helically to form a template from which microtubules grow. This assembly process requires higher-order oligomers of the coiled-coil protein Spc110 to bind multiple γTuSCs, thereby stabilizing the otherwise low-affinity interface between γTuSCs. While Spc110 oligomerization is critical, its N-terminal domain (NTD) also plays a role that is poorly understood both functionally and structurally. In this work, we sought a mechanistic understanding of Spc110 NTD using a combination of structural and biochemical analyses. Through crosslinking-mass spectrometry (XL-MS), we determined that a segment of Spc110 coiled-coil is a major point of contact with γTuSC. We determined the structure of this coiled-coil segment by X-ray crystallography and used it in combination with our XL-MS dataset to generate an integrative structural model of the γTuSC-Spc110 complex. This structural model, in combination with biochemical analyses of Spc110 heterodimers lacking one NTD, suggests that the two NTDs within an Spc110 dimer act independently, one stabilizing association between Spc110 and γTuSC and the other stabilizing the interface between adjacent γTuSCs.

Halogenation of Tris(amido)tantalacarboranes with Dihalomethanes CH2X2 (X = Cl, Br)

2002 ◽  
Vol 67 (6) ◽  
pp. 791-807 ◽  
Author(s):  
Mark A. Fox ◽  
Andrés E. Goeta ◽  
Andrew K. Hughes ◽  
John M. Malget ◽  
Ken Wade
Keyword(s):  
Single Crystal ◽  
Prolonged Exposure ◽  
Chemical Shifts ◽  
Amide Group ◽  
The Other ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Hydrolysis Of

Slow reactions of isomeric metallacarboranes of general formulae [(NMe2)3TaC2B9H11] (3 isomers) and [(NMe2)3TaC2B9H10Me] (3 isomers) with CD2Cl2 afford quantitative yields of monochloro complexes [Cl(NMe2)2TaC2B9H11] and [Cl(NMe2)2TaC2B9H10Me]. Exposure to CD2Cl2 for months leads to solutions containing about 70% of the dichlorides in three cases. More prolonged exposure of these and the other monochlorides leads to a mixture of boron-substituted complexes. Hydrolysis of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] by moist toluene results in the formation of the oxo-bridged complex 3,3'-[3,3-(NMe2)2-3,1,2-TaC2B9H11]2(μ-O), characterised by single-crystal X-ray crystallography. The limited solubility of the latter complex in CD2Cl2 eliminates the presence of this compound in the reaction of [3,3,3-(NMe2)3-3,1,2-TaC2B9H11] with CD2Cl2. The reaction of [2,2,2-(NMe2)3-2,1,12-TaC2B9H11] with CH2Br2 in C6D6 quantitatively yields the monobromide [2-Br-2,2-(NMe2)2-2,1,12-TaC2B9H11]. Prolonged reaction with CH2Br2 leads directly to isomeric boron-substituted complexes with no evidence for dibromides. The influence on 11B, 13C and 1H NMR chemical shifts of replacing an amide group in [(NMe2)3TaC2B9H11] with chloride to give [Cl(NMe2)2TaC2B9H11] is also discussed.

scholarly journals Two-Carbon Ring Enlargement of Five-, Six-, and Seven-Membered 1-Aza-2-vinylcycloalk-2-enes with Dimethyl Acetylenedicarboxylate and Subsequent Thermal Isomerization Reactions

2006 ◽  
Vol 61 (4) ◽  
pp. 385-395 ◽  
Author(s):  
Gerhard Maas ◽  
Robert Reinhard ◽  
Hans-Georg Herz
Keyword(s):  
Elevated Temperatures ◽  
Alder Reaction ◽  
Thermal Isomerization ◽  
Diels Alder ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
Ring Enlargement ◽  
Diels Alder Reaction ◽  
Carbon Ring ◽  
Electrocyclic Reaction

2-Aminodienes, in which the enamine function is incorporated in a five-, six-, or seven-membered ring, react with dimethyl acetylenedicarboxylate in a sequence of [2+2] cycloaddition and electrocyclic ring-opening to form the two-carbon ring expanded unsaturated heterocycles, i.e., 3,4- dicarboxylate substituted 6,7-dihydro-1H-azepines 3, 8 and 21, 1,6,7,8-tetrahydroazocines 22, and 6,7,8,9-tetrahydro-1H-azonines 13. Similarly, 2-[(2-thienyl)ethynyl]-4,5,6,7-tetrahydro-1H-azepine 9 is converted into 2-[(2-thienyl)ethynyl]-6,7,8,9-1H-azonine-3,4-dicarboxylate 10 which was characterized by X-ray structure determination. The eight- and nine-membered azaheterocycles 22 and 13, which have not been isolated, undergo thermal isomerization at elevated temperatures. Thus, ring contraction by a 6π-electrocyclic reaction takes place for N-methyl substituted azonine 13, while the N-allyl moiety of azocines 22 engages in an intramolecular Diels-Alder reaction or a 1,7- electrocyclization reaction

Crystal structure of the pseudoenzyme PDX1.2 in complex with its cognate enzyme PDX1.3: a total eclipse

2019 ◽  
Vol 75 (4) ◽  
pp. 400-415 ◽  
Author(s):  
Graham C. Robinson ◽  
Markus Kaufmann ◽  
Céline Roux ◽  
Jacobo Martinez-Font ◽  
Michael Hothorn ◽  
...  
Keyword(s):  
Active Sites ◽  
Protein Complexes ◽  
Structural Similarity ◽  
Cellular Protein ◽  
Vitamin B ◽  
Protein Activity ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Individual ◽  
High Degree

Pseudoenzymes have burst into the limelight recently as they provide another dimension to regulation of cellular protein activity. In the eudicot plant lineage, the pseudoenzyme PDX1.2 and its cognate enzyme PDX1.3 interact to regulate vitamin B6 biosynthesis. This partnership is important for plant fitness during environmental stress, in particular heat stress. PDX1.2 increases the catalytic activity of PDX1.3, with an overall increase in vitamin B6 biosynthesis. However, the mechanism by which this is achieved is not known. In this study, the Arabidopsis thaliana PDX1.2–PDX1.3 complex was crystallized in the absence and presence of ligands, and attempts were made to solve the X-ray structures. Three PDX1.2–PDX1.3 complex structures are presented: the PDX1.2–PDX1.3 complex as isolated, PDX1.2–PDX1.3-intermediate (in the presence of substrates) and a catalytically inactive complex, PDX1.2–PDX1.3-K97A. Data were also collected from a crystal of a selenomethionine-substituted complex, PDX1.2–PDX1.3-SeMet. In all cases the protein complexes assemble as dodecamers, similar to the recently reported individual PDX1.3 homomer. Intriguingly, the crystals of the protein complex are statistically disordered owing to the high degree of structural similarity of the individual PDX1 proteins, such that the resulting configuration is a composite of both proteins. Despite the differential methionine content, selenomethionine substitution of the PDX1.2–PDX1.3 complex did not resolve the problem. Furthermore, a comparison of the catalytically competent complex with a noncatalytic complex did not facilitate the resolution of the individual proteins. Interestingly, another catalytic lysine in PDX1.3 (Lys165) that pivots between the two active sites in PDX1 (P1 and P2), and the corresponding glutamine (Gln169) in PDX1.2, point towards P1, which is distinctive to the initial priming for catalytic action. This state was previously only observed upon trapping PDX1.3 in a catalytically operational state, as Lys165 points towards P2 in the resting state. Overall, the study shows that the integration of PDX1.2 into a heteromeric dodecamer assembly with PDX1.3 does not cause a major structural deviation from the overall architecture of the homomeric complex. Nonetheless, the structure of the PDX1.2–PDX1.3 complex highlights enhanced flexibility in key catalytic regions for the initial steps of vitamin B6 biosynthesis. This report highlights what may be an intrinsic limitation of X-ray crystallography in the structural investigation of pseudoenzymes.

scholarly journals A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis

2016 ◽  
Vol 12 ◽  
pp. 1870-1876 ◽  
Author(s):  
Mariano Goldberg ◽  
Denis Sartakov ◽  
Jan W Bats ◽  
Michael Bolte ◽  
Michael W Göbel
Keyword(s):  
Absolute Configuration ◽  
Reductive Amination ◽  
Kinetic Resolution ◽  
Aldol Reaction ◽  
Diels Alder ◽  
Base Catalysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Chemical Correlation ◽  
Brønsted Base

Starting from (S)-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound 10. In the crystals of the guanidinium benzoate salt the six membered rings of 10 adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine 10 catalyzes Diels–Alder reactions of anthrones and maleimides (25–30% ee). It also promotes as a strong Brønsted base the retro-aldol reaction of some cycloadducts with kinetic resolution of the enantiomers. In three cases, the retro-aldol products (48–83% ee) could be recrystallized to high enantiopurity (≥95% ee). The absolute configuration of several compounds is supported by anomalous X-ray diffraction and by chemical correlation.

scholarly journals Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dimethyl acetylenedicarboxylate: regioselective formation of 1:2 Michael type adducts

1993 ◽  
Vol 71 (4) ◽  
pp. 529-533 ◽  
Author(s):  
Kiyoshi Matsumoto ◽  
Yukio Ikemi ◽  
Motoo Shiro ◽  
Takane Uchida ◽  
James William Lown
Keyword(s):  
Resonance Structure ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
X Ray Crystallography ◽  
Michael Additions

Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dimethyl acetylenedicarboxylate afforded the 1:2 adducts regioselectively and, unexpectedly, in a Michael fashion rather than in a 1,3-dipolar manner. The structure of the products was established by X-ray crystallography. Regiospecific formation of the observed product 3 can be explained by the higher nucleophilicity of the nitrogen at the 2 position than at the 3 position of the 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizine 1 owing to the contribution of a resonance structure 5 to the hybrid. This favors two successive Michael additions to two equivalents of dimethyl acetylenedicarboxylate affording the observed 1:2 adducts 3.

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