Reactions of some substituted isoxazoles with organolithium reagents

The selectivity of metallation in 3- and 3,4-substituted 5-methylisoxazoles by n-butyl-lithium is determined by the influence of exo- and endo-cyclic heteroatoms. In contrast, both series of isoxazoles are metallated specifically at the C-5 methyl group by lithium di-isopropylamide.