Synthesis and Proton Nuclear Magnetic Resonance Spectra of Diastereomeric β-Hydroxy Esters. An Unusual Hydroxy to Methyl Coupling through Four ? Bonds

Article abstract of DOI:10.1021/jo00147a012

A series of 3-hydroxy-3-phenyl-2-alkylbutyrate esters has been prepared by the reaction of various ester enolates with acetophenone.A 1:1 mixture of diastereoisomers was obtained in each case which was conveniently separated by HPLC.The two isomers, erythro (e) or threo (t), were identified on the basis of their IR and NMR spectra.In CDCl3 solution only the erythro isomers exhibited a 1-Hz coupling constant between the hydroxyl and geminal methyl protons.This coupling is transmitted through four ? bonds which are arranged in a "W" configuration.In Me2SO solution,the intramolecular hydrogen bond which allows the "W" configuration is disrupted, causing coupling to disappear and the spectra of the erythro and threo isomers to become nearly equivalent.