2-Fluoro-4-phenylpyrimidine

Fluoro-5-phenyl-l,2,4-triazine (109, X = F) reacts much faster than the 3-chloro-, 3-bromo-, or 3-iodo-compound. Moreover, the reaction mixture obtained is cleaner than that from the corresponding 3-chloro- or 3-bromo compounds 3-amino-5-phenyl-l,2,4-triazine (110) is formed in good yield. This conversion takes place to only a small extent (18%) via the ANRORC process the main part of the aminodefluorination seems to involve the Sn(AE) mechanism. This result is consistent with the observation that the aminodefluorination of 4,6-diphenyl-2-fluoropyrimidine follows the Sn(AE) process, whereas 2-fluoro-4-phenylpyrimidine (position 6 is vacant for addition of the nucleophile) reacts for the most part according to the Sn(ANRORC) mechanism (see Section II,C,l,c). 

The nature of the leaving halogeno atom. It has been observed that reaction of mono-labeled 6-fluoro-, 6-chloro-, and 6-iodo-4-phenyl[l(3)- Njpyrimidine with potassium amide/liquid ammonia leads to 6-amino-4-phenylpyrimidine in which the exocyclic amino group is N-labeled the percentages, however, strongly depend on the nature of the halogen atom, i.e., F (73 5%), Cl (93 5%), Br (83 5%), I (13 5%) (Scheme 11.12) (72RTC1414). 

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