A report claiming that AcHisOMe reacts regiospecifically with 4-fluoronitrobenzene to give AcHis[tau Ph(NO2)]OMe, which on treatment with H2/Pd(C) undergoes a partial tau-pi shift to give some AcHis[pi Ph(NH2)]OMe, cannot be substantiated. 4(5)-Methylimidazole, a model for AcHisOMe, gives on reaction with 4-fluoronitrobenzene a 4:1 mixture of the regioisomers 1-(4-nitrophenyl),4-methylimidazole, corresponding to tau-substitution, and 1-(4-nitrophenyl),5-methylimidazole, corresponding to pi-substitution, each of which has been isolated and fully characterized, including proof of orientation. In both cases, treatment with H2/Pd(C) gives a single product, without any change of orientation in either case.

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http://dx.doi.org/10.1002/(SICI)1099-1387(199709)3:5%3C391::AID-PSC126%3E3.0.CO;2-8DOI Listing

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