The conformational properties of seven-membered heterocycles: 1,3-dioxacyclohept-5-ene and its 2-substituted derivatives

Abstract

1,3-Dioxacycloheptene and its 2-CH3, 2-OCH3, 2-t-Bu, and 2,2-dimethyl derivatives were studied by 1H and 13C dnmr methods. Substituent effects and the interpretation of spectral changes in 13C nmr at low temperature allow the determination of the most stable conformation of these compounds (TB for 1–4b and C for 5b) and the characterization of the dynamic processes observed for 2b, 4b, and 5b. The differences between the conformational and dynamic properties of the above compounds and their benzo analogs are rationalized in terms of different torsional interactions in the two series.