Alkylation hydrogen exchange

Larcher, A. V., Alexander, R., Rowland, S. J. and Kagi, R. I. (1986) Acid catalysis of alkyl hydrogen exchange and configurational isomerisation reactions acyclic isoprenoid acids. Organic Geochemistry 10, 1015. 

The mechanism of alkyl hydrogen exchange was not clarified, but a possible mechanism was postulated. Partial hydride abstraction by a Lewis acid site may have occured forming a carbocation-like species followed by exchange of a proton at a R-carbon. Such a mechanism predicts exchange to occur preferentially at methyl groups adjacent to the most stable carbocations (benzylic > 3° > 2° > 1°). This is consistent with the observed relative rates of epimerization of steranes during thermal maturation of sediments (83). 

This genera] scheme could be used to explain hydrogen exchange in the 5-position, providing a new alternative for the reaction (466). This leads us also to ask whether some reactions described as typically electrophilic cannot also be rationalized by a preliminary hydration of the C2=N bond. The nitration reaction of 2-dialkylaminothiazoles could occur, for example, on the enamine-like intermediate (229) (Scheme 141). This scheme would explain why alkyl groups on the exocyclic nitrogen may drastically change the reaction pathway (see Section rV.l.A). Kinetic studies and careful analysis of by-products would enable a check of this hypothesis. 

A variant of the H2/NH2 chemical exchange process uses alkyl amines in place of ammonia. Hydrogen exchange catalyzed by NH2 is generaHy faster using alkyl amines than ammonia, and a dual-temperature flow sheet for a H2/CH2NH2 process has been developed (69). 

Acid-catalyzed hydrogen exchange Halogenation Acylation and alkylation Mercuration Diazo coupling Nitrosation... 

Purine, 6-iodo-alkylation, 5, 530 synthesis, 5, 563, 597 Purine, 6-iodo-9- -D-(2,3,5-tri-0-acetyl)ribofuranosyl-synthesis, 5, 598 Purine, 9-isopropyl-deuterium-hydrogen exchange, 5, 527 Purine, 9-(2,3-0-isopropylidene-/3-D-ribofuranosyl)-6-methoxy-synthesis, 5, 584 Purine, 6-mercapto-biological activity, 5, 604 metabolism, 1, 237 as pharmaceutical, 1, 159 tautomerism, 5, 509 Purine, 2-methoxy-synthesis, 5, 596 Purine, 6-methoxy-irradiation, 5, 543 riboside... 

Tetrazole, 5-phenoxy-l -phenyl-mass spectra, 5, 801 photolysis, 5, 811 Tetrazole, 1-phenyl-deuterium-hydrogen exchange, 5, 806 mercuration, 5, 59 NMR, 5, 798 tautomerism, 5, 804 UV spectra, 5, 798 Tetrazole, 2-phenyl-NMR, 5, 798 tautomerism, 5, 804 UV spectra, 5, 798 Tetrazole, 5-phenyl-alkylation, 5, 818 anti-inflammatory activity, 5, 835 blowing agent, 1, 410 reactions... 

Thiazole, 2-acetylamino-4-methyl-alkylation, 6, 256 Thiazole, 2-acylamino-4-hydroxy-synthesis, 6, 297 Thiazole, 5-alkoxy-cleavage, 6, 289 synthesis, 6, 302 Thiazole, 2-alkyl-A7-alkylation, 6, 253 hydrogen exchange, 6, 276 methylation, 6, 253 quatemization, 6, 253-254 reactions, S, 88 Thiazole, 4-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 quatemization, 6, 253-254 Thiazole, 5-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 Thiazole, 2-alkylamino-tautomerism, 6, 248 Thiazole, 4-alkyl-2,5-dimethyl-quatemization, 6, 253-254 Thiazole, 2-alkylthio-reactions, S, 103 rearrangement, 5, 103 6, 291 Thiazole, 3-allyl-4-hydroxy-2-imino-synthesis, 6, 297 Thiazole, 2-allyloxy-rearrangement, 6, 289 Thiazole, 2-amino-diazo coupling, 6, 257 nitration, 6, 255... 

Xanthine, 8-ethyl-synthesis, 5, 574 Xanthine, 9-hydroxy-8-methyl-synthesis, S, 596 Xanthine, 1-methyl-deuterium-hydrogen exchange, S, 527 methylation, S, 533 occurrence, S, 598 reduction, 5, 541 synthesis, S, 589 Xanthine, 3-methyl-deuterium-hydrogen exchange, S, 528 methylation, S, 533 reduction, S, 541 synthesis, S, 595 Xanthine, 7-methyl-deuterium-hydrogen exchange alkylation, S, 527 reduction, S, 541 synthesis, S, 587 Xanthine, 8-methyl-synthesis, S, 574 Xanthine, 9-methyl-methylation, S, 533 nitration, 5, 538... 

R2NC1, 91, 92 phenyl acetate, Fries rearrangement of, 475 phenyacetyl halides, acylation by, 173 2-phenylbenzoic acid, cycliacylation, 185 phenyl ethers, alkylation of, 149 —, bromination of, 130 —, hydrogen exchange with, 260 —, rearrangement of, 476 phenyl ethyl mercury, mercuridemercuration of, 359, 360... 

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