Solvent Effects on Anchimerically Assisted Solvolyses. III. Solvent Effects on the Solvolyses of (1-Arylcycloalkyl)methyl p-Toluenesulfonates

Abstract

The solvolysis rates of (1-arylcyclobutyl)methyl and (1-arylcyclopropyl)methyl p-toluenesulfonates were measured in a wide variety of solvents. The aryl-assisted kΔ solvolysis of [1-(p-methoxyphenyl)cyclobutyl]methyl p-toluenesulfonate did not give a linear Winstein–Grunwald correlation using the 2-adamantyl-based YOTs scale, but did show dispersion for different binary solvent mixtures. An extended dual-parameter treatment, log (k/k80E) = mcYOTs + mΔYΔ, successfully correlated the present set of kΔ solvolyses with R > 0.995 and SD < 0.09. The blending parameter MΔ (= 0.51mΔ/(mc + 0.51mΔ)) increases monotonically with increased electron donation by the substituent, showing an increased dispersion of the YOTs plot with increasing anchimeric assistance. The solvolysis of (1-arylcycloalkyl)methyl p-toluenesulfonates demonstrates the varying extent of anchimeric assistance by the neighboring groups, from a completely synchronous aryl-assisted process for the p-methoxy derivative of (1-phenylcyclobutyl)methyl p-toluenesulfonate, via moderately to weakly aryl-assistance by the p-methyl derivative and the unsubstituted compound, to a completely aryl-unassisted kc process for the more electron-withdrawing aryl derivatives and the (1-arylcyclopropyl)methyl p-toluenesulfonates. The dual-parameter equation enables one to monitor the varying extent of anchimeric assistance in the transition state. From the results we propose a general solvolysis framework involving a continuous spectrum of kc − kΔ mechanisms for anchimerically assisted solvolysis.

Sixty Years of the Grunwald–Winstein Equation: Development and Recent Applications

“…(f) Correlation for solvolyses involving a 1,2-aryl shift Fujio and coworkers [65][66][67] have studied the solvent effects upon the specific rates of solvolysis of several tosylate esters in which there is the possibility of appreciable anchimeric assistance accompanying a 1,2-aryl shift (Equation (9). tosylate.…”

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

“…The equation including the hI term was very usefully applied [2, 29] to reactions involving a 1,2-aryl shift, where it can be shown to be equivalent to the original treatment [30, 31, 32]. It has the advantage that it would not require the development of new solvent ionizing power scales, requiring only the appropriate Y X scale, if the study was extended from a p -toluenesulfonate leaving group to other leaving groups.…”

Solvent Effects on the Solvolysis of Some Secondary Tosylates. Applications of YBnOTs and YxBnOTs Scales to Mechanistic Studies

“…35 Therefore, anchimeric assistance by an aryl group would not be significant in this system as has been suggested. 34 In conclusion, the present report indicates that both the newly developed Y xBnOTs scale and the YBnOTs scale previously stated are useful in the mechanistic study of the solvolysis of benzylic and related tosylates. Antiaromatic character of 9-fluorenyl cation in the solvolysis 9-fluorenyl tosylate (10) was doubted, and the presence or absence of anchimeric assistance in the solvolysis of 16-19 could be proved.…”

“…To explore whether or not these new scales of solvent ionizing power, Y xBnOTs and Y BnOTs , could be applied to other structurally different tosylates, literature data for certain substrates undergoing anchimerically assisted solvolyses [32][33][34] were examined. Table 9 presents the result of correlation analyses using Eqn.…”

“…Consequently, the transition state of phenonium ion type, such as 20, is likely to be involved in the solvolysis of activated substrates for 16-18 as has been considered. [32][33][34] For (1-arylcyclopropyl)methyl (19) tosylates, however, poor correlations were observed against Y xBnOTs even for the 4-methoxy derivative (19a). The use of Y BnOTs did not yield an excellent linear relationship, either.…”