The Retentive Solvolysis. VII. Structural Effect of the Leaving Group on the Steric Course of the S<scp>n</scp>1 Phenolysis of 1-Phenylethyl Systems

Abstract

Abstract A series of optically active 1-phenylethyl systems with various leaving groups has been phenolyzed in the phenolic solvents. The 1-phenylethyl systems with a negative leaving group (i.e., 1-phenylethyl chloride, bromide, 3,5-dinitrobenzoate, and tosylate) afforded 1-phenylethyl phenyl ether with a net retained configuration. In contrast, the 1-phenylethyl systems with a positively-charged leaving group (i.e., the 1-phenylethyldiazonium ion, the diethyl-(1-phenylethyl)-oxonium ion, and the protonated 2,6-di-t-butyl-4-methyl-4-(l-phenylethyl)-cyclohexadien-l-one) .gave the 1-phenylethyl phenyl ether with a net inverted configuration. These results provide further support for the view that the retentive Sn1 phenolysis proceeds via a four-center transition state between the phenol molecule and the ion-pair intermediate. Besides the phenolic ether, the o- and p-(1-phenylethyl)-phenols with net inverted configurations were obtained from all optically active substrates except 1-phenylethyl 3,5-dinitrobenzoate and the 1-phenylethyldiazonium ion. The 3,5-dinitrobenzoate gave the completely racemic o-alkylated phenol, along with the inverted p-alkylated phenol, whereas the diazonium ion afforded the o-alkylated phenol with a net retained configuration, together with the inverted p-alkylated phenol. The stereochemical and mechanistic implications of the C-alkylation are also discussed on the basis of the results of the acidic rearrangement of the phenolic ether under the Sn1 phenolysis conditions.