Mechanistic Studies in Triazolinedione Ene Reactions

• Published in: Synlett 2005-03, Vol.2005 (5), p.0713-0731
• Main Authors: Vougioukalakis, Georgios C., Orfanopoulos, Michael
• Format: Article
• Language: English
• Subjects: account
• ISSN: 0936-5214; 1437-2096
• DOI: 10.1055/s-2005-864793

Abstract Triazolinediones react with olefins bearing allylic hydrogens in an ene fashion to afford N-allylurazoles. This reaction, apart from considerable mechanistic attention, shows also substantial synthetic utility. Extensive experimental data, such as deuterium kinetic isotope effects, trapping of intermediates, and stereochemical studies, and to a lesser extent computational work, support a two-step mechanism with irreversible formation of a three-membered ring intermediate (aziridinium imide). On the basis of recent experimental and theoretical work, an open biradical has been proposed as the key intermediate. 1 Introduction and Background 2 Isotope Effects 3 Regioselectivity and Diastereoselectivity Studies 3.1 Regioselectivity 3.1.1 Regioselectivity with Simple Alkenes 3.1.2 Regioselectivity with Substituted Alkenes, Styrenes, α,β-Unsaturated Esters, Carbonyl Compounds and Sulfoxides 3.2 Diastereoselectivity 4 Solvent Trapping Studies 5 Stereochemistry: Simple Alkenes, Non-Polar Solvents 6 Theoretical Calculations 7 Concluding Remarks