Di‐ and Triarylmethylium Ions as Probes for the Ambident Reactivities of Carbanions Derived from 5‐Benzylated Meldrum's Acid. Issue 35 (5th August 2014)

• Record Type: Journal Article
• Authors: Chen, Xi; Tan, Yue; Berionni, Guillaume; Ofial, Armin R.; Mayr, Herbert
• Is Part Of: Chemistry. Volume 20:Issue 35(2014)
• Page Start: 11069
• Page End: 11077
• Publication Date: 2014-08-05
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201403161
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The kinetics of the reactions of carbocations with carbanions <bold>1</bold> derived from 5‐benzyl‐substituted Meldrum's acids <bold>1‐H</bold> (Meldrum's acid=2, 2‐dimethyl‐1, 3‐dioxane‐4, 6‐dione) were investigated by UV/Vis spectroscopic methods. Benzhydryl cations Ar₂CH⁺ added exclusively to C‐5 of the Meldrum's acid moiety. As the second‐order rate constants (<italic>k</italic>_C) of these reactions in DMSO followed the linear free‐energy relationship lg <italic>k</italic>=<italic>s</italic>_N(<italic>N</italic>+<italic>E</italic>), the nucleophile‐specific reactivity parameters <italic>N</italic> and <italic>s</italic>_N for the carbanions <bold>1</bold> could be determined. In contrast, trityl cations Ar₃C⁺ reacted differently. While tritylium ions of low electrophilicity (<italic>E</italic>&lt;−2) reacted with <bold>1</bold> through rate‐determining β‐hydride abstraction, more Lewis acidic tritylium ions initially reacted at the carbonyl oxygen of <bold>1</bold> to form trityl enolates, which subsequently reionized and eventually yielded triarylmethanes and 5‐benzylidene Meldrum's acids by hydride transfer.</p> </abstract>