Thermal Reactions of Tributyltin Hydride with α-Azido Esters:  Unexpected Intervention of Tin Triazene Adducts under Both Nonradical and Radical Conditions

• Published in: Journal of organic chemistry Vol. 70; no. 8; pp. 3046 - 3053
• Main Authors: Benati, Luisa, Bencivenni, Giorgio, Leardini, Rino, Minozzi, Matteo, Nanni, Daniele, Scialpi, Rosanna, Spagnolo, Piero, Zanardi, Giuseppe
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-04-2005
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties; Organic azide; Nitrogen heterocycle; Thermal reaction; Ketone; Ester; Malonic acid derivatives; Amine; Aminoester; Cyclization; Organic free radical; Benzene; Triazene derivatives; Triazole derivatives; Ketoester; Chemical synthesis; Organic stannane
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0478095

Thermal reaction of various α-azido esters with Bu3SnH in refluxing benzene results in smooth production of 3-(tributylstannyl)-1-triazene adducts affording cyclized 1,2,3-triazol-4-ones in preference to reduced amines and thence provides a new useful method for the preparation of these triazole derivatives. In the presence of AIBN the occurrence of triazene products still remains important or even exclusive and, consequently, generation of the expected stannylaminyl radicals is seriously limited. With 2-azidomalonates and α-azido-β-keto esters stannyltriazenes can similarly occur in the absence of the radical initiator, but in the latter cases the ensuing triazenes undergo preferential cyclization onto the ketone moiety to give reactive hydroxytriazolines. Contrary to α-azido esters, in the presence of AIBN α-azido-β-keto esters as well as azidomalonates give rise only to the usual stannylaminyl radicals. A possible explanation for the different behavior of the mono- and dicarbonyl azides in the presence of AIBN is put forward.