Theoretical study on the BF3-catalyzed meinwald rearrangement reaction

The mechanisms of the BF3-catalyzed Meinwald rearrangement reactions of five epoxides in dichloromethane solution have been studied at the M062X/6-311++G(2df,2pd) level. Accordingly, the Lewis acid-epoxide complex can react through several alternative pathways, though three phases (ring opening, C-C bond rotation, and hydrogen or alkyl group migration) are required in any path. In some cases, a concerted pathway (involving all three successive phases) is found. Otherwise, the reaction takes place through a reaction mechanism involving a zwitterion or a BF3 addition compound (formed by fluoride transfer from the BF3 moiety to the incipient carbocationic center generated by C-O bond rupture) or both as reaction intermediate(s). The BF 2-bound fluorohydrin yields the reaction product through a concerted process involving fluoride transfer from the C-F bond to the OBF2 group and hydrogen or alkyl group migration, as first demonstrated in this work. Effects of a number of features (solvent effects, concurrent hydrogen/alkyl group migration, carbocation substitution, benzylic conjugation) are also discussed. © 2014 American Chemical Society.Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2011-28124) and the Gobierno de Aragón (Group E11) is gratefully acknowledged.Peer Reviewe

Triazolinediones as Highly Enabling Synthetic Tools

Triazolinediones (TADs) are unique reagents in organic synthesis that have also found wide applications in different research disciplines, in spite of their somewhat "exotic" reputation. In this review, we offer two case studies that demonstrate the possibilities of these versatile and reliable synthetic tools, namely, in the field of polymer science as well as in more recently emerging applications in the field of click chemistry. As the general use of triazolinediones has always been hampered by the limited commercial and synthetic availability of such reagents, we also offer a review of the available TAD reagents, together with a detailed discussion of their synthesis and reactivity. This review thus aims to serve as a practical guide for researchers that are interested in exploiting and further developing the exceptional click -like reactivity of triazolinediones in various applications