Intermolecular migration

The chiral information of stereogenic centers in the allyl moiety of the precursor is destroyed on deprotonation. While an i/3-bound ion pair with a planar carbon frame is a chiral compound, usually rapid racemization takes place by intra- or intermolecular migration of the cation from one face to the opposite one. The sole exceptions known at present are secondary 2-alkenyl carbamates with X = dialkylaminocarbonyloxy21, in which the cation is tied by the chelating ligand, see Section 1.3.3.3.1.2. 

Deuteration experiments suggested an intra- as well as an intermolecular migration of the acyl group. / -Methoxybenzoyl- and / -nitrobenzoylimidazole did not undergo acyl migration upon irradiation. Af-Crotyl- and TV-geranylimidazoles are stable to irradiation. 

RADIATION-SENSITIVE GROUPS. Although the absorption of radiation energy is dependent only on the electron density of the substrate and therefore occurs spatially at random on a molecular scale, the subsequent chemical changes are not random. Some chemical bonds and groups are particularly sensitive to radiation-induced reactions. They include COOH, C-Hal, -SO2-, NHz, C=C. Spatial specificity of chemical reaction may result from intramolecular or intermolecular migration of energy or of reactive species -free radicals or ions. 

On the other hand, an intermolecular migration of silyl groups also takes place among 5-methyl-2-(trialkylsilyl)thiophenetricarbonylchromium(0) complexes under basic conditions45. Increased steric hindrance from the silyl groups (see entry 34 of Table 1) results in preferential deprotonation. 

A study of the kinetics of isomerization of nitroaminothiazoles [227-229] showed that both intramolecular and intermolecular migration of the nitro group occur [228], The following reaction mechanism was proposed (Scheme 22). 

The va r of an aromatic hydrocarbon is passed through the sulfonic acid at 150-200°, and water is removed by the excess hydrocarbon vapor. Chlorobenzene has been substituted for the aromatic hydrocarbon in this reaction. Intermolecular migration of the sulfonic acid group occurs in some cases. 

Szocs [246] has studied the rate of decay at higher temperatures of samples subjected to excess pressure. At a pressure of 1 atm and a temperature of 100°C, the rate of decay is more than 100 times that at 100°C and 5000 atm. If the pressure is 5000 atm, free radicals can still be observed at 160°C. According to Szocs, the large influence of pressure indicates that the decay is due to intermolecular migration of free radicals. The radicals interact with neighbouring segments and are transferred and disappear by combination when then they meet other radicals. 

Co(en)3] and [Co(en)3] (all three exchange processes are between high-spin Co(II) and low-spin Co(III)). This is consistent with the ability of phen ligands to use their tt-orbitals to facilitate the intermolecular migration of an electron from one ligand to another, and phen complexes tend to exhibit fast rates of self-exchange. 

Bonded carbohydrate complexes of platinum-group metals have been comprehensively reviewed, as has the dibutyltin-mediated selective derivatization of compounds with three or more hydroxy groups. An intermolecular migration... 

To demonstrate the selectivity of intramolecular acyl migration over intermolecular migration a competitive experiment was devised in which chemical ligation of S-protected (a-aminoacyl)tripeptide(128) (via an 11-membered cyclic transition state) was carried out in the presence of five equivalents of a dipeptide (H-Gly-Leu-OH, 129). As shown by HPLC, the ligated product (130) contained no intermolecular acyl migration products (131 or 132) (Scheme 34). 

Heating the HCl salts of arylalkylamines renders intermolecular migration of the alkyl groups. 

Chambers RD, Cheburkov YA, Tanabe T, Vaughan JFS (1995) An intermolecular migration of trifluoromethyl anion. J Fluor Chem 74 227-228... 

PPhs react with 163a, only dicarbonyl vinylidenes 164f and 164g are obtained. Mechanistic studies indicate that the intermolecular migration proceeds by a radical pathway. 

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