Synthesis of isoxazoloazaborines via gold(I)-catalyzed propargyl aza-Claisen rearrangement/borylative cyclization cascade

Isoxazoloazaborines 3 and 5 have been synthesized from 4-N-propargylaminoisoxazole 1 via gold(I)-catalyzed propargyl azaClaisen rearrangement followed by electrophilic borylative cyclization in 27-86% yields. In situ generation of isoxazole 2 having an amino group and allenyl functionality is essential to give highly substituted isoxazoloazaborines 3 and 5, although the conventional propargyl aza-Claisen rearrangement readily affords the corresponding nitrogen-containing heterocycles, such as pyridines and pyrroles. The resulting isoxazoloazaborine 5a underwent the N-O bond insertion of zinc carbenoid to give oxazine-fused azaborine 6 in 48% yield.

Automated summary

This paper reports the synthesis of benzoisoxazoloborines via gold(I)-catalyzed propargyl azaClaisen rearrangement and electrophilic borylative cyclization. The in situ generation of aminoisoxazole intermediate with allenyl functionality is crucial for obtaining highly substituted compounds. Furthermore, the N-O bond insertion of a zinc carbenoid was used to synthesize oxazine-fused azaborine.