Selective Preparation of Fluorene Derivatives Using the t-Butyl Function as a Positional Protective Group

Several 4-substituted 2,7-di-t-butylfluorene derivatives (3) were prepared by electrophilic substitutions of 2,7-di-t-butylfluorene (1). 4-Substituted fluorene (4), such as 4-bromo- (4a), 4-methyl (4e), and 4-acetylaminofluorene (4j), were obtained by the trans-t-butylations of 3. Although we attempted to synthesize 1,8-disubstituted fluorene from 3,6-di-t-butylfluorene (2) which was derived from 2,2′-diiodo-4,4′-di-t-butyldiphenylmethane (5), by the same methods, we obtained only 2,7-disubstituted fluorene derivatives (8); it turned out electrophilic substitutions of 2 gave 2,7-disubstituted 3,6-di-t-butylfluorene derivatives.