Stereochemistry of seven-membered heterocycles. 3. Conformation of 5,6-dichloro-1,3-dioxacyclopent-5-enes and the planar-fragment effect

Abstract

1. It is shown by dipole-moment measurements and IR and PMR spectroscopy that 2-R-5,6-dichloro-1, 3-dioxacyclohept-5-enes (R=C6H5, p-ClC6H4, p-NO2C6H4 and the corresponding cyclohexanone ketal exist in the flexible form; the 2-t-butyl analog exists in a chair-e-twist equilibrium depending on the polarity of the medium. 2. It is shown that a conformational planar-fragment effect occurs as a result of shielding of the C-Cl and C-H bonds in the chair form. © 1981 Plenum Publishing Corporation