Structural and conformational study of pyrazolobenzodiazonine and pyrazolobenzodiazecine skeletons

A study of the structure and the conformational preferences of nine- and ten-membered rings of the corresponding pyrazolo[1,5-a][6,1]benzodiazonine and pyrazolo[1,5-a][7,1]benzodiazecine skeletons have been performed via dynamic NMR (variable temperature experiments), B3LYP/6-31G(d) DFT calculations and single-crystal X-ray diffraction analysis. The experimental values found for energy barrier to enantiomerisation due to ring inversion revealed high conformational stability of the nine-membered ring compared to the corresponding ten-membered one.