Differential Bridging in the Solvolysis of Epimeric Bicyclic Sulfonates, Norbornanes, Part 17

Abstract

Abstract The solvolysis rates and products of the 2‐ exo ‐ norbornyl, bicyclo[3.2.1]oct‐8‐yl, bicyclo[3.3.1]non‐2‐yl, bicyclo[3.2.1]oct‐6‐yl, bicyclo[3.2.1]oct‐2‐yl and bicyclo[3.2.2]non‐6‐yl p ‐toluenesulfonates 10–15 , respectively, are reported. The exo/endo rate ratios for these epimeric secondary tosylates in 80% EtOH varied from 1125 for 11 to 1.6 for 15 . The relative rates varied between 2278 for exo ‐ 10 and 4 ·10 −3 for endo ‐ 11 . The hydrolysis products were mainly rearranged alcohols and olefins. The unrearranged alcohols from the exo ‐tosylates were formed with complete or predominant retention of configuration, whereas those derived from the endo ‐tosylates were mostly inverted. These results confirm the hypothesis that relative rates, as well as products, are largely determined by the degree of bridging between the cationic center and a dorsal C‐atom in the transition state and in the resulting ion pairs. Since bridging is a directed bonding interaction, it is subject to the same angle and conformational strains as ordinary covalent bonds. But bridging requires less geometrical change than the formation of normal bonds and of nonclassical ions.