SYNTHESIS AND CONFORMATIONAL ANALYSIS OF 16H-DINAPHTHO AND 12 H-DIBENZO [D,G][1,3,2]DIOXASILOCINE

Abstract

The conformation of the heterocyclic eight-membered ring in 16H-dinaphtho and 12H-dibenzo [d,g][1,3,2]dioxasilocine was investigated in solution by ¹H NMR spectroscopy. The barrier to ring inversion in the 16H-dinaphtho compound 3a was found to be 8.6±0.2 Kcal/mol and for the 12 H-dibenzo compound 4a, 8±0.2 Kcal/mol. Molecular mechanics calculations show three energy minima conformations for both compounds, boat chair(BC), twist boat(TB) and twist boat boat(TBB). Twist boat form is estimated to be the global minimum for the dibenzo compounds while TBB is the global conformation of the dinaphtho compounds. The result of molecular mechanics calculations are supported by analysis of the ¹H-NMR spectra.