Nucleophilicities and carbon basicities of pyridines.

Rate and equilibrium constants for the reactions of pyridines with donor-substituted benzhydrylium ions have been determined spectrophotometrically. The correlation equation log k(20 degrees C)=s(N+E), in which s and N are nucleophile-specific parameters and E is an electrophile-specific parameter, has been used to determine the nucleophilicity parameters of various pyridines in CH(2)Cl(2) and aqueous solution and to compare them with N of other nucleophiles. It is found that the nucleophilic organocatalyst 4-(dimethylamino)pyridine (DMAP) and tertiary phosphanes have comparable nucleophilicities and carbon basicities despite widely differing Brønsted basicities.

The DMAP-catalyzed acetylation of alcohols--a mechanistic study (DMAP = 4-(dimethylamino)pyridine).

The acetylation of tert-butanol with acetic anhydride catalyzed by 4-(dimethylamino)pyridine (DMAP) has been studied at the Becke3 LYP/6-311 + G(d,p)//Becke3 LYP/6-31G(d) level of theory. Solvent effects have been estimated through single-point calculations with the PCM/UAHF solvation model. The energetically most favorable pathway proceeds through nucleophilic attack of DMAP at the anhydride carbonyl group and subsequent formation of the corresponding acetylpyridinium/acetate ion pair.

Rates and equilibria of the reactions of tertiary phosphanes and phosphites with benzhydrylium ions.

The kinetics of the reactions of benzhydrylium ions and quinone methides with eight tertiary phosphanes and two phosphites were investigated photometrically. The nucleophilicity parameters N and slope parameters s of these nucleophiles were derived according to the equation log k(20 degrees C) = s(N + E). Correlations of the nucleophilicity parameters N with pK(Ha) and sigma(p) values as well as with the rate constants of reactions with other electrophiles are discussed.

Structure-nucleophilicity relationships for enamines.

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.

Pi-nucleophilicity in carbon-carbon bond-forming reactions.

Which electrophiles react with which nucleophiles? The correlation log k(20 degrees Celsius) = s(E + N), in which electrophiles (carbocations, metal-pi-complexes, diazonium ions) are characterized by one (E) and nucleophiles are characterized by two parameters (N, s), proved to be applicable for a wide variety of electrophile-nucleophile combinations. Since the introduction of this correlation in 1994 (Angew. Chem.