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When the same substrate is treated with sodium amide under pressure, surprisingly, the result is the normal amino product of the Chichibabin reaction. Specific examples are described below. When 4-tert-butylpyridine (79)was heated with a mixture of xylene and sodium amide under 350 psi nitrogen pressure, allowing the hydrogen gas to escape through a pressure relief valve as the reaction proceeded, a yield of 74% 2-amino-4-tert-butylpyridine (80) was obtained. On the other hand, at atmospheric pressure coupling took place to (81) (Scheme 3 1).
Very little success has been reported for aromatic amines. A. ARYLAMINATION It is sufficient to mention that Chichibabin and Zeide found that pyridine with sodium anilide gave a very low yield of 2-phenylaminopyridine (14MI1). There have been no improvements reported in the literature since their discovery. During the amination of pyridine, it was observed that 2,2'-dipyridylamine(71) was formed as a by-product (23RTC240). The formation of 71, as the result of the attack of the sodium salt of 2-aminopyridine (88) on pyridine, occurs to a larger extent during the preparation of 2,6-diaminopyridine (65),where higher temperatures are required (Scheme 34) (72UP1).
A + (64) Sec. C] ADVANCES IN THE CHICHIBABIN REACTION 27 SCHEME 25 26% yield. It is recorded in the literature that the atmospheric amination of nicotinic acid gave 13% 2,6-diaminopyridine (65) (56RC621). Nicotinamide (66), under pressure, gave 17% 6-aminonicotinamide (67) and 7% 64. Under atmospheric pressure, a 20% yield of 2-aminonicotinamide (68) was obtained (Scheme 23) (44JA1479). B. AMINATION OF 2-SUBSTITUTED PYRIDINES Pressure amination of 2-picoline (I) led to a ring-opening/ring-closure reaction giving m-phenylenediamine (69) as the principal product (Scheme 24).