Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines?

Organic & Biomolecular Chemistry Pub Date: 2011-06-28 DOI: 10.1039/C1OB05745F

Abstract

N-(2-Azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N′-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C[double bond, length as m-dash]C or the distal C[double bond, length as m-dash]N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.

Graphical abstract: Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines
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