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Some methylquinolines have also been observed to undergo, at least to a small extent, this abnormal reaction. In the case of 8-methylquinoline ( 1 IS), the normal product, 2-arnino-S-methylq&oline (1 19), was obtained in 33‘><,yield and a very small amount of the abnormal product, 2-amino-3,4-dihydro-8-methylquinoline, isolated as its hydrolyzed product, 3,4-dihydro-8-methylcarbostyril(120), was obtained in 1% yield (Scheme 48) (67CPB 19 10). In a similar manner, 7-methylquinoline was treated with sodium amide to give 2-amino-3,4-dihydro-7-methylquinoline, isolated as 3,4-dihydro-7methylcarbostyril (4%).
The yield was a function of reaction time and temperature; prolonged heating decreased the yield, and the optimum temperature was in the range 130-140°C (73MI1). Preferential attack at the 2-position of 3-substituted pyridines is a general phenomenon in the Chichibabin reaction (64CJC1627). 5: 1 ratio of 2amino-3-methylpyridine to 2-amino-5-methylpyridine (see Section IV,A). The amination of 3-n-butylpyridine (99)yielded 50% of a 4: 1 mixture of 2-amino3-n-butylpyridine (100):2-amino-5-n-butylpyridine (101) (Scheme 39).
Dimers and tars are known to result from heating pyridine or derivatives with sodium metal. A two-step procedure has been reported, in which the first step consisted of preforming an alkyl sodium amide, followed by attack of the alkyl amide on a pyridine ring at the 2-position with subsequent liberation of a hydride ion. The S,(AE) mechanism, analogous to the standard Chichibabin reaction, is proposed (83EUP009170A2, 83USP4405790; 87MIP1). In this manner, the reaction was cleaner and the yields were better than under the conditions of Vajda and Kovacs, in which the heterocycle and alkylamine were required to react simultaneously with alkali metals, thus yielding appreciable amounts of dimers and tarry materials.
Advances in Heterocycling Chemistry. Vol. 44 by Author Unknown