Spirans. 16. 3,3′-Spirobi[3,4-dihydro-2H-[1,3]oxazino[3,2-a]benzimidazole] and Its Thia Analogue

Abstract In order to obtain spiran the sodium derivative of o-phenylenediamine was subjected to reaction with 1,3-dibromo-2,2-bis(bromomethyl)propane in N,N-dimethylformamide. The compound was also synthesized by the reaction of the sodium derivative of 2,3-dihydro-1H-benzimidazol-2-one with 1,3-dibromo-2,2-bis(bromomethyl)propane. By this procedure the thia analogue of the spiran was obtained. In both cases the condensation route was unexpected. This is due to the fact that the solvent (DMF) takes part in the reaction and a stereo-electronic situation occurs, which is similar to that covered by Bredt’s exclusion rule.