Reaction of 3-phenylisoxazole with alkyllithiums

Alkyllithiums react with 3-phenylisoxazole giving C₅-H abstraction followed either mainly by ring fragmentation to benzonitrile and ethynolate ion (in the case of t-BuLi) or (less hindered alkyllithiums: n-BuLi, EtLi, MeLi) also by formation of alkylated enaminones. Appreciable amounts of 2-alkyl-4,6-diphenylpyrimidines have also been isolated for certain alkyllithiums (EtLi and MeLi). This is at variance with the reported behaviour with hindered lithium amides (LTMP) for which only C₅-H abstraction followed by ring fragmentation was described. The mechanistic significance of the observed results is discussed.