Thermal aryl rearrangement

A thermally induced rearrangement of arylhydrazones of furoxan-3-carbonyl compounds into 2-aryl-5-[(hydroximino)arylmethyl]-2//-l,2,3-triazole 1-oxides has been observed for the first time.156 2-(2,2-Dicyano-l-hydroxyethenyl)-l-methylpyrroles (192) are readily rearranged to their 3-isomers (193) in nearly quantitative yield when heated to 75-142 °C. The inter- or intra-molecular auto-protonation of a pyrrole ring... 

In general, the aromatic Claisen rearrangement can be illustrated by equation 68. The initial step in the thermal Claisen rearrangement of an aUyl aryl ether leads to an ortho-dienone which usually enolizes rapidly to form the stable product, an ort/io-allylphenol (so-called orf/zo-Claisen rearrangement, 147 148 149). However, if the rearrange-... 

Many a-aryl derivatives of chromium decompose thermally or rearrange on hydrolysis to give bis(7r-arene)chromium(0) compounds. Most of these transformations are exceedingly complex and a multitude of products are formed. 

A symmetry approach to the effect of temperature and substitution on Cope rearrangements has revealed that with increasing temperature the loss of symmetry can be considered as a collective variable which has a positive linear relationship with temperature. The results of an aromatic Cope rearrangement of a trans-l-aryl-2-ethenylcyclobutanecarbonitrile have been reported for the construction of the fused benzocyclooctene ring. The effects of gem-dimethyl substitution on the cyclopropane, alkene geometry, relative stereochemistry of the cyclopropane, and steric and electronic effects of functional groups on the thermal Cope rearrangement of divinylcyclopropanes have been reported (Scheme 10). " ... 

Thermal pericyclic rearrangement of an aryl allyl sulphone ArSOzCR R -CR =CR R at ca. 290 C places the aryl substituent at the y-position of the allylic system, SO2 being eliminated to give ArCR R CR =CR R. Isomerization to the vinyl sulphone can occur with t-butyl allyl sulphones on treatment with K2CO3 in acetone. 

Imidazole, 2-amino-1 -methyl-4,5-diphenyl-tautomerism, 5, 368 Imidazole, 2-aroyl-mass spectra, 5, 360 synthesis, 5, 391, 402 UV spectra, 5, 356 Imidazole, 4-aroyl-synthesis, 5, 474 Imidazole, C-aroyl-UV spectra, 5, 356 Imidazole, aryl-nitration, 5, 396, 433 oxidation, 5, 433 Imidazole, 1-aryl-dipole moments, 5, 351 dearylation, 5, 449 ethylation, 5, 448 H NMR, 5, 353 hydroxymethylation, 5, 404 rearrangement, 5, 108 synthesis, 5, 390 thermal rearrangement, 5, 363 Imidazole, 2-aryl-chlorosulfonation, 5, 397 synthesis, 5, 475 Imidazole, 4-aryl-bromination, 5, 399 Imidazole, C-aryl-electrophilic substitution, 5, 432-433 nitration, 5, 433 Imidazole, N-aryl-reactions, 5, 448-449 structure, 5, 448-449 Imidazole, arylmercapto-... 

Aryl migrations are promoted by steric crowding in the initial radical site. This trend is illustrated by data from the thermal decomposition of a series of diacyl peroxides. The amount of product derived from rearrangement increases with the size and number of substituents ... 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

In contrast to the allylic sulfenates mentioned so far, cinnamyl trichloromethanesulfenate (9), prepared by the usual method, can be isolated and is relatively stable. Furthermore, its rearrangement to cinnamyl trichloromethyl sulfoxide (i.e., without allylic isomerization, equation 7), proceeds at a relatively slow rate (in CC14 at 80.0 °C, k = 3.90 x 10 5s 1). This result also contrasts with the observation mentioned earlier that cinnamyl arenesulfinate rearranges to a-phenylallyl aryl sulfone33,34. Similar behavior has been detected for y, y-dimethylallyl ester 11 which undergoes thermal isomerization to sulfoxide 12 (equation 8)36-38. 

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