Fluorene, 9,9-disubstituted synthesis

The synthesis of 2-monosubstituted or 2,2 -disubstituted precursor compounds can be achieved by two different routes direct electrophilic aromatic substitution or the use of substituted derivatives of 9-fluorenone. hi many cases, the first route is complicated due to the fact that the two fluorene moieties in spirobifluorene react chemically independently of each other. The formation of products monosubstituted in the 2-position is therefore often accompanied by the formation of byproducts (Fig. 6). A good example is the nitration of spirobifluorene, which was investigated by Weisburger and coworkers [23]. They discovered that a careful control of reaction times and conditions allowed for the formation of 2-nitro-9,9 -spirobifluorene or 2,2 -dinitro-9,9 -spirobifluorene as the main product. Especially in the case of 2-nitro-9,9 -spirobifluorene, however, the conversions are low because the reaction must be quenched before a suitable amoimt of the dinitro compound is formed. 

Wang, Y.-H., Bailey, J.F., Petersen, J.L. and Wang, K.K. (2011) Synthesis of 5-(2-methoxy-l-naphthyl)- and 5-[2-(methoxymethyl)-l-naphthyl]-llH-benzo[f)]fluorene as 2,2 -disubstituted l,l -binaphthyls via benzannulated enyne-allenes. Beilstein Journal of Organic Chemistry, 7, 496-502. 

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