SYNTHESIS AND CONFORMATIONAL DYNAMICS OF ,8,8'-TETRAMETHYL-3,3'-SPIROBI[2,4-BENZODITHIEPIN]

The title compound 1 was prepared in one step from 1,2-bis(chloro meth yl)-4,5-dimethylbenzene and sodium trithiocarbonate generated in situ from carbon disulfide, hydrogen sulfide, and sodium ethoxide in ethano l. Conformational analysis of 1 has been carried out using H-1- and C- 13-NMR spectroscopy, X-ray analysis, and semiempirical calculations. T he results indicate that in the solid state 1 exists in a chair-twist- boat conformation while in solution it undergoes two intramolecular dy namic processes, pseudorotation at lower temperature (similar to 250 K ) and ring inversion at higher temperature (similar to 280 K), with th e activation energies (Delta G(double dagger)) of approximately 54 and 56 kc/mol, respectively. ............................................ ..goes two intramolecular dynamic processes, pseudorotation at lower t emperature (similar to 250 K) and ring inversion at higher temperature (similar to 280 K), with the activation energies (Delta G double dagg er) of approximately 54 and 56 kc/mol, respectively.