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Crystal structure of 4-(6-chloropurin-9-yl)-3-phenyl-4,5,6,6a-tetrahydro-3aH-cyclopenta[d]isoxazol-6-ol, C17H14N5O2Cl
No full textThe title compound crystallizes in the space group Pna21, with a = 10.124(5), b = 14.335(3), c = 11.113(2) Å. There is no conjugation between the purine moiety and the cyclopentane ring, whereas there is some conjugation between the isoxazoline and the phenyl rings. The chiral centers C3a, C4, C6a, C6 are either S, S, R, R or R, R, S, S respectively, because of the glide planes. The molecules are linked by intermolecular hydrogen bonds and van der Waal's forces
Crystal structure of 1-phenylamino-2-phenyl-4-p-chlorophenylimidazole, C21H16N3Cl
No full textThe condensation of amidrazones with alpha-bromoketones through ring closure affords two isomeric products. The minor product was subjected to X-ray diffractometric analysis and turned-out to be a substituted imidazole. The title compound crystallizes in space group P2(1)/c, with a = 11.838(2); b = 13.249(1); c = 11.226(2) Angstrom, beta = 91.01(1)degrees. The packing of molecules is determined by a hydrogen bond N - H ... N (2.908(5))
Synthesis and Synthetic Applications of 1,2,4-Oxadiazole-4-Oxides
No full textThe first 1,2,4-oxadiazole-4-oxide was prepared by Wieland a century ago, but-this compound remained largely a chemical curiosity until very recently. 1,2,4-Oxadiazole-4-oxides are a family of heterocycles closely related to the chemistry of nitrile oxides which were actively studied in the past half century and provided the basic knowledge on 1,2,4-oxadiazole-4 -oxides. The dimerizations of nitrile oxides under acidic or basic conditions were thoroughly studied by different research groups, and offer the more common entries to the symmetrical substituted 1,2,4-oxadiazole-4-oxides. A more general route to symmetrical and unsymmetrical substituted 1,2,4-oxadiazole-4 -oxides is based on the nitrile oxide cycloadditions to amidoximes. A variety of other 1,2,4-oxadiazole-4-oxides forming reactions are also known in the literature. Many of these reactions were neither fully exploited nor mechanistically understood since they require unusual starting reagents, often difficult to prepare, or take place affording complex mixtures of products. Some of these methods still await for improved procedures and proper mechanistic attention to be of general use and will be reviewed shortly.
The chemistry of 1,2,4-oxadiazole-4-oxides is related to the fragility of the heterocyclic ring, which undergoes thermal or photochemical cycloreversion to nitriles and nitrosocarbonyl intermediates. Trapping of the nitrosocarbonyls takes place easily with dienes and enes, affording a variety of hetero Diels-Alder and ene adducts, which attract great interest because of their useful synthetic elaboration toward many natural products of potential pharmaceutical applications.
The high efficiency of the photochemical cleavage of 1,2,4-oxadiazole-4-oxides at room temperature or well below affords the softest entry to the nitrosocarbonyls and allows for the study of their chemistry under convenient and simple experimental conditions. The photochemical cleavage have been applied successfully to Solid Phase chemistry, allowing for a safe and environmental friendly methodology for the synthesis of important intermediates.
This report is comprehensive of the synthesis and synthetic applications of the 1,2,4-oxadiazole4-oxides
Enantioselectively-Catalyzed Reactions with (E)‐2-Alkenoyl-pyridines, Their N‐Oxides, and the Corresponding Chalcones
No full text1. Introduction
2. Michael Reaction
2.1. Phospha- and Aza-Michael Reactions
2.2. Henry Reaction
2.3. Friedel−Crafts Reaction
3. Epoxidation Reaction
4. Radical Reaction
5. [3 + 2] Dipolar Cycloaddition Reaction
6. D.A. Reaction
6.1. Families of Unusual Catalysts for the D.A.
Reaction
6.1.a. Natural and Artificial Metalloenzymes
6.1.b. DNA-Based Asymmetric D.A. Reaction
7. Hetero D.A. Reaction
8. Influence of Substituents on Reactivity and
Selectivity
9. Relationship between Different Organocatalysts
or Chiral Complexes and the Stereochemical
Outcome
10. Comparison between the Enantioselectively-
Catalyzed Reactions with (E)-2-Alkenoyl-pyridines,
Their N-Oxides, and the Corresponding
Chalcones
11. Conclusions
Associated Content
Supporting Information
Author Information
Corresponding Author
Notes
Biographies
Acknowledgments
Dedication
Reference
Classical and non-classical secondary orbital interactions and Coulombic attraction in regiospecific dimerization of acrolein
No full textNon-classical (bridging) and classical (Woodward-Hoffmann) secondary orbital interactions as well as a favourable electrostatic interaction are involved in the stabilization of the two lowest transition passes of the acrolein dimerization. The heteroatoms provide anchimeric assistance to the hetero Diels-Alder reaction through a neighbouring-group mechanism
Enantioselective Catalytic Reactions with N-Acyliden Penta-atomic Aza-heterocycles. Heterocycles as Masked Bricks To Build Chiral Scaffolds
No full textCONTENTS
1. Introduction 9922
2. Epoxidation Reactions 9925
3. Cyclopropanation Reactions 9929
4. Michael Reactions 9930
4.1. Aza-Michael Reactions 9945
4.2. Sulfa-Michael Reactions 9949
4.3. Phospha-Michael Reactions 9951
5. Radical Reactions 9953
6. Diels−Alder Reactions 9956
7. 1,3-Dipolar and Formal [3+2] Cycloaddition
Reactions 9959
8. Influence of Substituents on Reactivity and
Selectivity 9964
9. Comparison between Catalytic, Enantioselective
Reactions with Different 1-(Nitrogen-heterocyclic)-
Substituted Prop-2-en-1-ones 1−9 and the
Aromatic Analogues 10 9968
10. Relationship between Different [Chiral Ligand/
Inorganic Cation] Complexes or Non-Racemic
Organocatalysts and the Stereochemical Outcome
9969
11. Conclusions 997
An unexpected bispericyclic transition structure leading to 4+2 and 2+4 cycloadducts in the endo dimerization of cyclopentadiene
No full textThe stereospecific endo dimerization of cyclopentadiene takes place through an asynchronous and symmetrical bispericyclic transition structure, which shows a merging of the 4+2 and 2+4 cycloaddition paths. The shape of the transition structure testifies to the presence of attractive Salem/Houk secondary orbital interactions assisting the endo approach
Synthesis of tetrazole- and imidazole-based compounds: prophetic molecules made real for biological studies
No full textThe synthesis of tetrazole- and imidazole-based derivatives has been achieved via sulfur nucleophilic ringopening
of 2-oxiranyl-alcohols or chlorides. The derivatives obtained may represent interesting new chemical
tools to investigate biological functions and in particular the mitochondrial molecular chaperone TRAP1. The
results are discussed in the light of the availability of these molecules according to the proposed synthetic
procedures
A photochemical generation of nitrosocarbonyl intermediates
No full textNitrosocarbonyl intermediates are photochemically generated from 1,2,4-oxadiazole-4-oxides and efficiently trapped with enes and dienes
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