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Di‐ and Triarylmethylium Ions as Probes for the Ambident Reactivities of Carbanions Derived from 5‐Benzylated Meldrum’s Acid
Author(s) -
Chen Xi,
Tan Yue,
Berionni Guillaume,
Ofial Armin R.,
Mayr Herbert
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403161
Subject(s) - chemistry , carbanion , moiety , carbocation , reactivity (psychology) , electrophile , medicinal chemistry , nucleophile , hydride , lewis acids and bases , reaction rate constant , photochemistry , kinetics , organic chemistry , catalysis , hydrogen , medicine , physics , alternative medicine , pathology , quantum mechanics
The kinetics of the reactions of carbocations with carbanions 1 derived from 5‐benzyl‐substituted Meldrum’s acids 1‐H (Meldrum’s acid=2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione) were investigated by UV/Vis spectroscopic methods. Benzhydryl cations Ar 2 CH + added exclusively to C‐5 of the Meldrum’s acid moiety. As the second‐order rate constants ( k C ) of these reactions in DMSO followed the linear free‐energy relationship lg k = s N ( N + E ), the nucleophile‐specific reactivity parameters N and s N for the carbanions 1 could be determined. In contrast, trityl cations Ar 3 C + reacted differently. While tritylium ions of low electrophilicity ( E <−2) reacted with 1 through rate‐determining β‐hydride abstraction, more Lewis acidic tritylium ions initially reacted at the carbonyl oxygen of 1 to form trityl enolates, which subsequently reionized and eventually yielded triarylmethanes and 5‐benzylidene Meldrum’s acids by hydride transfer.