Cycloaddition reactions conformations

IH-Azepine, 1-methoxy carbonyl-cycloaddition reactions, 7, 522 with nitrosobenzene, 7, 520 tricarbonyliron complex acylation, 7, 512-513 conformation, 7, 494 tricarbonylruthenium complex cycloaddition reactions, 7, 520 1 H-Azepine, l-methoxycarbonyl-6,7-dihydro-synthesis, 7, 507... 

Schmidt reaction of ketones, 7, 530 from thienylnitrenes, 4, 820 tautomers, 7, 492 thermal reactions, 7, 503 transition metal complexes reactivity, 7, 28 tungsten complexes, 7, 523 UV spectra, 7, 501 X-ray analysis, 7, 494 1 H-Azepines conformation, 7, 492 cycloaddition reactions, 7, 520, 522 dimerization, 7, 508 H NMR, 7, 495 isomerization, 7, 519 metal complexes, 7, 512 photoaddition reactions with oxygen, 7, 523 protonation, 7, 509 ring contractions, 7, 506 sigmatropic rearrangements, 7, 506 stability, 7, 492 N-substituted mass spectra, 7, 501 rearrangements, 7, 504 synthesis, 7, 536-537... 

N-alkylation, 4, 236 Pyrrole, 2-formyl-3,4-diiodo-synthesis, 4, 216 Pyrrole, 2-formyl-1-methyl-conformation, 4, 193 Pyrrole, 2-formyl-5-nitro-conformation, 4, 193 Pyrrole, furyl-rotamers, 4, 546 Pyrrole, 2-(2-furyl)-conformation, 4, 32 Pyrrole, 2-halo-reactions, 4, 78 Pyrrole, 3-halo-reactions, 4, 78 Pyrrole, 2-halomethyl-nucleophilic substitution, 4, 274 reactions, 4, 275 Pyrrole, hydroxy-synthesis, 4, 97 Pyrrole, 1-hydroxy-cycloaddition reactions, 4, 303 deoxygenation, 4, 304 synthesis, 4, 126, 363 tautomerism, 4, 35, 197 Pyrrole, 2-hydroxy-reactions, 4, 76 tautomerism, 4, 36, 198... 

Tellurophene, 2-methylmercapto-conformation, 4, 944 Tellurophene, 2-phenyl-irradiation, 4, 946 mass spectra, 4, 942 photolysis, 4, 42 Tellurophene, tetrachloro-synthesis, 4, 118, 963 Tellurophene, tetradeutero-synthesis, 4, 964 Tellurophene, tetrahydro-conformation, 4, 938, 944 IR spectra, 4, 942 mass spectra, 4, 24, 943 PE spectroscopy, 4, 26 reactions, 4, 88, 958 ring strain, 4, 28 synthesis, 4, 118, 962, 963 Tellurophene, tetraphenyl-cycloaddition reactions, 4, 951... 

How do orbital symmetry requirements relate to [4tc - - 2tc] and other cycloaddition reactions Let us constmct a correlation diagram for the addition of butadiene and ethylene to give cyclohexene. For concerted addition to occur, the diene must adopt an s-cis conformation. Because the electrons that are involved are the n electrons in both the diene and dienophile, it is expected that the reaction must occur via a face-to-face rather than edge-to-edge orientation. When this orientation of the reacting complex and transition state is adopted, it can be seen that a plane of symmetry perpendicular to the planes of the... 

Repeat your analysis for Z,Z-hexa-2,4-diene, and again calculate the energy to twist the diene into the same conformation as seen in the Diels-Alder transition state (Z,Z-hexa-2,4-diene+TCNE). Compare the two twisting energies , and rationalize the observed relative rates for the two cycloaddition reactions. 

In contrast to those unreactive dienes that can t achieve an s-cis conformation, other dienes are fixed only in the correct s-cis geometry and are therefore highly reactive in the Diels-Alder cycloaddition reaction. 1,3-Cyclopentadiene, for example, is so reactive that it reacts with itself. At room temperature, 1,3-cycIopentadiene dimerizes. One molecule acts as diene and a second molecule acts as dienophile in a self Diels-Alder reaction. 

The reaction of several substituted imidazo[4,5-c/]-, pyrazolo[3,4-r/]- and triazolo[4,5-zf]pyrid-azines 3 with ynamines, in competition with [4 + 2] cycloaddition, leads to [2 + 2] derivatives 4, which rearrange to l,2-diazocines5.7 8 The reaction seems to be sensitive to the substituents, as replacement of the electron-withdrawing group R on the pyridazine ring of the pyrazolo compound (A = N, B = CH) by chlorine completely inhibits both the [4 + 2] and [2 + 2] cycloaddition reactions. The X-ray structure of the imidazo derivative 5 (R = Ms, A = CH, B = N) reveals a tub conformation of the eight-membered ring. 

V-Acyliminium ions act as dienophiles in [4 + 2] cycloaddition reactions with conjugated dienes13, while A-acylimimum ions that (can) adopt an x-cis conformation are able to act as heterodienes in an inverse electron demand Diels-Alder process with alkenes or alkynes3 (see Section D. 1.6.1.1.). 

The diastereofacial selectivity of this asymmetric [3C+2S] process is explained following a model similar to that described in Sect. 2.6.4.4 for the reaction of chiral alkenylcarbene complexes and 1,3-dienes. Thus, the proposed mechanism that explains the stereochemistry observed assumes a [4+2] cycloaddition reaction between the chromadiene system and the C=N double bond of the imine. The necessary s-cis conformation of the complex makes the imine... 

Some of its special chapters are the Pericyclic Reactions, which includes Cheletropic, Electrocyclic, Sigmatropic and Cycloaddition reactions. The concept of Stereochemistry and Conformation deserve special attention not because they cater to the needs of higher students, but they are immensely useful for candidates trying for UGC and CSIR sponsored competitive examinations, but also those preparing for Union Public Service Commission and State Public Service Commission Exams. The candidates will find the chapters immensely useful and is sure to rouse interest in them in knowing more about mechanistic chemistry. 

While the perfluorinated acetates do prefer insertion, they are still capable of forming 1,3-dipoles and have demonstrated interesting effects on the regioselectivity of intramolecular cycloaddition reactions, presumably through Lewis acid-mediated effects on the dipolarophile [83]. Other chemoselectivity effects have been noted in the intramolecular cycloaddition reactions and may or may not be partially induced by conformation and sterics [84]. It was further demonstrated thaL when possible, O-H insertion is the predominant outcome over other types of insertion for rhodium]II)-car-benes, independently of the catalyst. However, cycloaddition reactions have been demonstrated to be hgand-dependent [85]. 

Padwa et al. (187,188) concisely summarized his domino cycloaddition/ A -acyliminium ion cyclization cascade process, which involves sequentially the generation of an isomiinchnone 1,3-dipole, intramolecular 1,3-dipolar cycloaddition reaction, 77-acyliminium ion formation, and, hnally, Mannich cyclization. Kappe and co-workers (189) utilized Padwa s cyclization-cycloaddition cascade methodology to construct several rigid compounds that mimic the putative receptor-bound conformation of dihydropyridine-type calcium channel modulators. 

The 3-acyl-2(3F/)-oxazolones function as good dienophiles in cycloaddition reactions with cyclic 2,4-dienes such as cyclopentadienes and anthracenes. Thus, the thermal reaction of 3-acetyl-2(37/)-oxazolone with cyclopentadiene and the hexachloro and hexamethyl derivatives gives endo-cycloadducts exclusively. In particular, the chiral cycloadducts 221 and 223 derived from the diastereoselective Diels-Alder reactions of 3-(2-exo-alkoxy-l-apocamphanecarbonyl)-2(3/7)-oxazo-lones with hexamethylcyclopentadiene and 9,10-dimethylanthracene, respectively, are highly useful as chiral 2-oxazolidinone auxiliaries. The conformationally rigid roofed structures play a crucial role in affording excellent chiral induction (Fig. 5.54). 

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