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.