Rearrangement stability

An important difference between Fnedel-Crafts alkylations and acylations is that acyl cations do not rearrange The acyl group of the acyl chloride or acid anhydride is transferred to the benzene ring unchanged The reason for this is that an acyl cation is so strongly stabilized by resonance that it is more stable than any ion that could con ceivably arise from it by a hydride or alkyl group shift... 

Although this cleavage is probably driven by the stability of benzyl cation evidence has been obtained suggesting that tropyhum cation formed by rearrangement of benzyl cation IS actually the species responsible for the peak... 

This IS a frequently used proce dure for the preparation of alkenes The order of alcohol reactivity paral lels the order of carbocation stability R3C > R2CH > RCH2 Benzylic al cohols react readily Rearrangements are sometimes observed... 

This synthetic appproach has been used in a few cases for the preparation of pyridazines from diazo compounds and cyclopropenes. In general, cycloadducts (176) are formed first and these rearrange in the presence of acid or alkali to pyridazines (Scheme 98) (69TL2659, 76H(5)40l). Tetrachlorocyclopropene reacts similarly and it was found that the stability of the bicyclic intermediates is mainly dependent on substitution (78JCR(S)40, 78JCR(M)0582>. 

From the results quoted in Section 4.04.2.1.3(x) the stability of acetyl derivatives of indazolone decreases in the order Af(l)-acetyl >A (2)-acetyl > 0(3)-acetyl. The reactivity of 3-hydroxypyrazoles is covered by Dorn s comprehensive review (80CHE1). Amongst the results reported there are the Claisen rearrangement of allyloxypyrazoles (475a) (475b)... 

In some cases, especially in the presence of strongly electron attracting substituents, isomerization to acid amides has been observed, probably preceded by deprotonation at ring carbon. Even (56), known for its stability towards common alkali, undergoes this rearrangement when a lithium amide is used as the base (80JOC1489). 

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... 

Diaziridine, 3-benzyl-1,3-dimethyl-inversion, 7, 7 Diaziridine, 1,2-dialkyl-reaction with iodides, 7, 217 thermal decomposition, 7, 217 Diaziridine, dibenzoyl-rearrangement, 7, 214 Diaziridine, 3,3-dimethyl-Raman spectra, 7, 202 Diaziridine, fluoro-synthesis, 7, 232 Diaziridines acylation, 7, 213 from azomethines, 7, 231 calculations, 7, 198 from chloramine, 7, 230 cycloaddition reactions, 7, 28 electron diffraction, 7, 19 199 c/s-fused NMR, 7, 201 hydrolysis, 7, 216 inversion stability, 7, 200... 

MO calculations, 7, 364 Oxetene, 2-isopropylidene-polysubstituted rearrangement, 7, 377 Oxetene, tetramethyl-structure, 7, 366 Oxetenes, 7, 363-402 decomposition, 7, 375 metabolism, 1, 243 molecular dimensions, 7, 366 thermal stability, 7, 370 Oxetenyl anions aromaticity, 7, 371 Oxetenyl cations aromaticity, 7, 371 Oxichlororaphine occurrence, 3, 196 Oxichromic developers in colour photography, 1, 378-379 Oxidation... 

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