The kinetics of the reactions of benzhydryl cations with 22 enamines, three pyrroles, and three indoles were investigated photometrically in dichloromethane. The nucleophilicity parameters N and slope parameters s of these electron-rich pi-systems were derived from equation log k (20 degrees C)=s(E+N) and compared with the nucleophilicities of other pi-systems (silyl enol ethers, silyl ketene acetals) and carbanions. It is shown that the nucleophilic reactivities of enamines cover more than ten orders of magnitude, comparable to enol ethers on the low reactivity end and to carbanions on the high reactivity end. Since the products of N-attack are thermodynamically less stable than the reactants, the observed rate constants refer to the formation of the carbon bond;carbon bonds. In some cases, equilibrium constants for the formation of iminium ions were measured, which allow one to determine the intrinsic rate constants of these reactions.

Keywords: Electrophilicity / Nucleophilicity / Kinetics / Linear free-energy relationships / Quinone methides Novel synthetic routes to the aryl-substituted quinone methides 3a-f have been developed, and a previously reported Mannich approach has been used for the syntheses of the acceptor substituted quinone methides 2e-g. The secondorder rate constants for the reactions of 3c-f and 2e-g with the carbanions 9a-h were determined photometrically in DMSO. With Equation (1), log k 2 = s (N + E), and the known nucleophilicity parameters N and s for the carbanions 9a-h,

Aq uantitative Lewis acidity/basicitys cale toward boron-centeredL ewis acids has been developed based on a set of 90 experimental equilibrium constantsf or the reactions of triarylboranes with various ON N-, Sand nd P-centered Lewis bases in dichloromethane at 20 8C. Analysis with the linear free energy relationship log K B = LA B + LB B allowse quilibrium constants, K B ,t ob ec alculated fora ny type of borane/Lewisb ase combination through the sum of two descriptors, one for Lewisa cidity (LA B)a nd one for Lewis basici-ty (LB B). The resultingL ewis acidity/basicity scale is independento ff ixed reference acids/bases and valid for various types of trivalent boron-centered Lewisa cids. It is demonstratedt hat the newly developed Lewisa cidity/basicity scale is easily extendable through linear relationshipsw ith quantum-chemically calculated or common physical-organic descriptorsa nd known thermodynamic data (DH BF 3). Furthermore,t his experimental platform can be utilized fort he rationald evelopment of borane-catalyzed reactions.

Acid‐free Friedel–Crafts chemistry: A paradox? Nucleophilicity scales, based on reactions with benzhydrylium ions, show that many π systems are more nucleophilic than aqueous or alcoholic solutions that are generally employed as solvents for SN1 reactions. Solvolytically generated carbocations can, therefore, be trapped by donor‐substituted arenes and alkenes to form products of Friedel–Crafts‐type reactions in neutral aqueous solutions (see scheme).

The reactivities of cyclic enones and α,β-unsaturated lactones were characterized by following the kinetics of their reactions with colored carbon-centered reference nucleophiles in DMSO at 20 °C. The experimentally determined...