Solvolysis in Carboxamides. V. Solvolytic Elimination of threo-1-Methyl-2-phenylpropyl Brosylate in N,N-Dimethylacetamide. Kinetic, Product, and Deuterium Tracer Studies

Abstract

Abstract Solvolysis of a series of ring substituted threo-1-methyl-2-phenylpropyl brosylates has been carried out in N,N-dimethylacetamide (DMA) as solvent. Hammett treatment of the rate data indicated that the DMA solvolysis of the unsubstituted brosylate (1c) falls into the category of ks pathway (100%). In order to gain further information of the nature of the ks pathway, the DMA solvolysis of 1c or 1c-2-d (labeled at C(2)) has been conducted. The product distribution, effect of water content on it, the composition and deuterium distribution of recovered brosylate, kinetic isotope effect, and the deuterium distribution of product have been investigated. The products consisted of the olefins ((E)- and (Z)-2-pheny1-2-butenes, and 2- and 3-phenyl-1-butenes), and, in the presence of water in DMA, the carboxylates (erythro- and thero-1-methyl-2-phenylpropyl acetates) and the small amount of diastereomeric alcohols. The major product was (Z)-2-phenyl-2-butene, indicating the occurrence of anti-E1 process. The deuterium was substantially scrambled in each product. These findings suggest that the reaction proceeds through tight ion-pair and subsequent processes such as anti-E1, 2,1-phenyl and -hydride shifts, solvent capture, and threo-erythro interconversion take place competitively. In view of a substantial extent of intervention of such rearrangement, the involvement of nucleophilic solvent assistance is thought to be less probable in this ks process.