Ring transformations of 2,3-dihydroisoxazoles via azomethine ylides—formation of annulated 5- and 7-membered N-heterocycles☆

Abstract On thermal activation the 2,3-dihydroisoxazoles 12 – 14 are transformed into annulated dihydroazepines 15 – 17 as main products, besides minor amounts of the corresponding pyrrole derivatives 18 – 20 . In the proposed mechanism the azomethine ylides of type III and VI are involved as intermediates which undergo 1,5- and 1,7-ring closure reactions, respectively.