Conversion of a 3-Oxaquadricyclane to a Substituted Cyclobutane. Preparation and Proton Magnetic Resonance Spectra of Four Stereoisomeric 1,2-Diacetyl-3,4-dicarbomethoxycyclobutanes

Abstract

Reaction of l,5-dicarbomethoxy-2,4-dimethyl-3-oxaquadricyclane with water gave a mixture of cis,cis,cis- and cis,cis,trans-1,2-diacetyl-3,4-dicarbomethoxycyclobutanes. The latter on treatment with acid epimerized to the corresponding trans,trans,trans-isomer, whereas the former yielded the trans,trans, cis-epimer together with 3,10-dimethyl-3,10-epoxy-5,8-dioxo-4,9-dioxatricyclo[5.3.0.02,6]decane which contains a new bridged ring system. The structure and stereochemistry of each compound was derived from symmetry considerations as reflected in its p.m.r. spectrum, and was facilitated by selective deuteration experiments. Vicinal and long-range spin–spin interactions between the cyclobutane ring hydrogens were deduced from pertinent p.m.r. sub-spectra using the NMRIT–NMREN computer program.