Ring-Closure Reactions. 19. Kinetics of Formation of Benzo-Crown Ethers by Intramolecular Nucleophilic Substitution. A Comparison between Poly(oxyethylene) and Polymethylene Chains

Article abstract of DOI:10.1021/ja00404a027

Kinetic data have been obtained for the formation of 9-, 12-, 15-, 21-, 30-, and 48-membered benzo-crown ethers by intramolecular Williamson synthesis in Me2SO-water (99:1, v/v).Comparison with earlier data for the formation of catechol polymethylene ethers provides an insight into the influence on the ease of ring closure of the replacement of methylene groups by oxygen atoms.Little or no effect occurs at ring size 9.In the next higher homologues the ease of cyclization of the poly(oxyethylene) chains is some 3 times as great as that of the polymethylene chains of similar length, but in the limit of the very long chains the two series behave much in the same way.Interestingly, literature data related to the fast, encounter-controlled reactions between end groups linked by poly(oxyethylene) and polymethylene chains reveal much the same features of the slow, activation-controlled reactions.The general picture fits in with well-established conformational arguments based on the expected strain relief due to replacement of trasannular CH...HC interactions with CH...O or O...O interactions.The oxygen atom effect turns out to be a sensitive tool for the detection of even weak strain energies in ring compounds.