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

• Published in: Organic & biomolecular chemistry Vol. 9; no. 19; p. 6741
• Main Authors: Alajarin, Mateo, Bonillo, Baltasar, Ortin, Maria-Mar, Orenes, Raul-Angel, Vidal, Angel
• Format: Journal Article
• Language: English
• Published: England 07-10-2011
• Subjects: Azides - chemistry; Cyclization; Imides - chemistry; Imines - chemistry; Molecular Structure; Quinazolines - chemical synthesis; Quinazolines - chemistry; Stereoisomerism
• ISSN: 1477-0539
• DOI: 10.1039/c1ob05745f

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=C or the distal C=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.