Preparation of carbazole and dibenzofuran derivatives by selective bromination on aromatic rings or benzylic groups with B-bromosuccinimide

摘要

N-Bromosuccinimide (NBS), a bromine source, has been used to study the bromination of toluidine and cresols systematically to clarify the underlying mechanism and the orientation effect. It has been found that bromination of toluidine and cresols which possess electron-donating NH2/OH with NBS gives electrophilic aromatic substitution products quickly instead of the desired benzylic bromination products. In contrast, when the electronic effect of the substituted groups is reversed, only the benzylic bromination products are gained. Based on this methodology, several potential AChE inhibitors, such as 2-methoxy-5-(benzylamino)mefhyl-dibenzofuran, 3-bromo-2-methoxy-5-met-hyl-9H-carbazole, 3,6-dibromo-2-methoxy-5-methyl-9H-carb-azole, and 5-(bromomethyl)-2-methoxy-9H-(phenylsulfonyl)-carbazole have been synthesized.