Paper
On the occurrence of an SN(ANRORC) mechanism in the amination of 2-substituted 4-phenylpyrimidines with potassium amide in liquid ammonia†‡
Published Sep 2, 2010 · A. P. Kroon, H. Plas, G. V. Garderen
Recueil des Travaux Chimiques des Pays-Bas
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Abstract
On amination of 2-X-4-phenylpyrimidine [X = SCH3, SO2CH3, SC6H5, SO2C6H5, SCN, CN, (CH3)3] with potassium amide in liquid ammonia at - 33° and/or -75°, 2-amino-4-phenylpyrimidine is in general formed as the main product. Depending on the substituent in position 2, several by-products are formed: when X is N(CH3)3, some bis(4-phenyl-2-pyrimidinyl)amine is obtained; in the case of X = SCN. a considerable amount of (4-phenyl-2-pyrimidinyl) disulfide is formed, while for X = SCH3 and SC6H5, 3-amino-3-phenylacrylonitrile is produced. It is proved, using 2-X-4-phenyl-[1,3-15N]-pyrimidines, that the formation of the 2-amino compound can occur by a ring opening/ring closure sequence [SN(ANRORC) mechanism]. The percentage of the compounds which react by this mechanism is found to be 91% for X = SCH3, 73% for X = SO2CH3, 34% for X = SO2Ph, 90% for X = SCN, 5% for X = CN and 10% for X = N(CH3)3. By PMR spectroscopy of solutions of 2-X-4-phenylpyrimidine (X = SCH3 and SO2CH3) in liquid ammonia, containing potassium amide, good evidence is found for the presence of Meisenheimer σ-adducts, formed by an addition of the amide ion to C(6) of the pyrimidine ring.
The formation of 2-amino-4-phenylpyrimidine in liquid ammonia can occur by a ring opening/ring closure sequence, with a high percentage of compounds reacting by this mechanism.
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