Heterocyclic synthesis by π-acidic metal catalyzed reactions via n-o bond cleavage

This review contains recent progress in heterocyclic synthesis by π-acidic metal catalyzed reactions via N-O bond cleavage. The reaction involving a terminal N-O bond (R+-O-) predominantly proceeds via nucleophilic attack of the O atom and subsequent formation of an π-oxo carbenoid intermediate through N-O bond cleavage. In contrast, the reaction of oximes and hydroxylamine derivatives having an internal N-O bond (R-OR') is initiated by the nucleophilic attack of either N or O atom. In addition, hydroxylamine derivatives have been utilized as an external reagent in the cyclization reaction. The methodology produces a wide variety of highly functionalized nitrogen and oxygen heterocycles in an efficient manner under mild reaction conditions.