Pyridine, 2-amino-, p-bromination

Pyran, tetrahydro-, 3 chloro 2 methyl [2H Pyran, tetrahydro, 3 chloro-2-mcthyl ], cis, trans mixture, 55, 64 2-PYRAZOLIN-5-ONES, 3-alkyl-, 55, 73 2-Pyrazolin 5-one, 3-(l-propyl)-, 55, 73 Pyridine, 2-amino-, p-bromination of, 55, 23... 

Pyridine, 2-amino, p-brommabon of, 55, 23 Pyridine, 2-amino-6-methyl-, p-bromination of 55, 23... 

All four isomeric selenolopyridines which can be derived from benzoselenophene (423— 426 Scheme 123) have been described. Ethyl 3-hydroxyselenolo[2,3-fe]pyridine-2-carboxy-late (429) has been prepared as shown in Scheme 124 (73BSF704). Treatment of ethyl 2-chloropyridine-3-carboxylate with methaneselenol yields (427). Nucleophilic displacement of bromine in bromoacetic acid with subsequent loss of methyl bromide yields (428), which after esterification is cyclized under Dieckmann conditions to give (429). The parent compound (423 colorless oil with b.p. 92 °C/1 mmHg) is prepared either by cyclization of compound (430) and subsequent decarboxylation of the intermediate acid (equation 57) or by reduction of 2-nitroselenophene and subsequent condensation of the amino compound with malonaldehyde bis(diethyl acetal) in the presence of zinc chloride (equation 58) (76BSF883). Selenolo[3,2-6]pyridine (426 b.p. 127-129°C/10 mmHg m.p. 35.5-37.0°C) has been obtained in an analogous manner. 

As in benzene chemistry, electron-releasing amino groups facilitate electrophilic substitution, so that, for example, 2-aminopyridine undergoes 5-bromination in acetic acid even at room temperature this product can then be nitrated, at room temperature, forming 2-amino-5-bromo-3-nitropyridine. Bromina-tion of all three amino-pyridines is best achieved with iV-bromosuccinimide at room temperature, products being 2-amino-5-bromo-, 3-amino-2-bromo- and 4-amino-3-bromopyridines. Similarly, chlorination of 3-amino-pyridines affords 3-amino-2-chloro-pyridines. Nitration of amino-pyridines in acid solution is also relatively easy, with selective attack of 2- and 4-isomers at P-positions. A mechanistic study of dialkylamino-pyridines showed nitration to involve attack on the salts. ... 

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