fluorenyyli

Fluorenyyli, also written as fluorenyl or fluoren-9-yl, denotes the aryl substituent derived from fluorene by removal of a hydrogen at the 9-position. The fluorenyl fragment is attached to another molecule through that central carbon and is commonly encountered in organic synthesis as a protecting-group handle or as a reactive synthetic handle.

Chemical structure and naming

The fluorenyl group is based on the fluorene framework, a rigid, polycyclic aromatic hydrocarbon consisting of two benzene rings fused to a central five-member ring. When used as a substituent, the linkage is through the 9-position carbon, yielding the fluoren-9-yl moiety. In many contexts the term fluorenyl refers to the neutral radical or the corresponding fluorenyl anion or cation, depending on the reaction medium, but the common practical usage is as a bulky aryl substituent.

Preparation and reactivity

Fluorenyl derivatives are typically prepared by functionalizing fluorene at the 9-position, for example by chloromethylation to give fluorenylmethyl derivatives or by forming carbonate or chloride reagents used to install the fluorenyl group onto nucleophiles. The fluorenyl moiety is valued for its stability and conjugation, which can delocalize charge and increase the steric bulk of the substituent.

Uses

A major use of the fluorenyl group is as a protecting group in peptide and organic synthesis, most notably the 9-fluorenylmethoxycarbonyl (Fmoc) system for amine protection in SPPS. Fluorenyl-containing dyes and materials are also explored in organic electronics and photophysics due to the rigid, planar, highly conjugated framework.

See also

Fluorene; 9-Fluorenylmethyl carbamate (Fmoc); fluorenide (the fluorenyl anion).