Electrophilicity parameters for 2-benzylidene-indan-1,3-diones—a systematic extension of the benzhydrylium based electrophilicity scale

Abstract

Kinetics of the reactions of four 2-benzylidene-indan-1,3-diones (1a-d) with carbanions (2a-I) have been studied photometrically in dimethyl sulfoxide solution at 20 degrees C, and the electrophilicity parameters E were determined by the linear free energy relationship log k(2)(20 degrees C) = s(N + E) (eqn (1)). The rate-determining step of these reactions is the nucleophilic attack of the carbon nucleophile at the double bond of the Michael acceptor. Comparisons with literature data show that the linear free energy relationship (eqn (1)) allows the semiquantitative prediction of the reactivities of 2-benzylidene-indan-1,3-diones towards various nucleophiles.

Mechanism and Linear Free Energy Relationships in Michael‐Type Addition of 4‐Substituted Anilines to Activated Olefin in Acetonitrile

“…Recently, Mayr and co‐wokers have demonstrated that the linear free energy relationship (Eq. ) can also be employed for describing the rates of typical Michael addition . In this equation, k is the second‐order rate constant, s is the nucleophile‐specific slope parameter, N represents the nucleophilicity parameter, and E is the electrophilicity parameter: …”

Electrophilicities of 1,2‐Disubstituted Ethylenes

“…The most reactive compound in this series of 1,2-disubstituted ethylenes, maleic anhydride (1a), has an electrophilic reactivity similar to that of diethyl azodicarboxylate, [27] benzylidene indandione, [28] or an acylazolium ion, [29] but it is less electrophilic than the gem-substituted bis(phenylsulfonyl)ethene. [30] The reactivity of the double bond decreases by approximately three orders of magnitude when the bridging oxygen in 1a is substituted by a methylimino group in N-methyl maleimide (1b), which has a reactivity similar to that of a palladium-stabilized 1,3-diarylallyl cation, [31] a 1,2-diaza-1,3-diene, [32] or β-nitrostyrene.…”

Direct Nucleophilic SN1‐Type Reactions of Alcohols

“…[13] Strong electron-donating substituents enhance the stability of the carbocations. [14] Benzylic carbocations are of moderate stability and high reactivity (e.g., mesitylbenzylic carbocation is positioned at +6 on the Mayr scale) and are capable of reacting with a large variety of nucleophiles. Because of the low ability of the alkynyl group to stabilize a positive charge, reactions of propargyl cations are quite limited.…”