Proton and carbon-13 nuclear magnetic resonance studies of the conformational properties of seven-membered heterocycles. 2,4-Benzodithiepin and its derivatives

Abstract

The conformational properties of 1,3-dithia-5,6-benzocycloheptene (7) (2,4-benzodithiepin), three 2,2-dialkyl derivatives, and two monosubstituted derivatives (2-CH3 and 2-OCH3) have been investigated by 1H and 13C dnmr methods. It is reported that the most stable conformation of the seven-membered ring is a chair on which, in the case of the monosubstituted compounds, the 2-CH3 group adopts an equatorial position while the 2-OCH3 group takes the axial position. Only for the 2,2-pentamethylene derivative (10) was a minor amount (13%) of TB form detected. These results are markedly different from those found previously for the oxygen analogs and the conformational effect of the cyclic heteroatoms will be discussed in terms of the anomeric and steric effects.