STEREOSELECTIVE ELECTROCHEMICAL SYNTHESIS AND CATHODIC BEHAVIOUR OF (9-exo-BENZYL-η6-FLUORENE)CHROMIUM TRICARBONYL

Article abstract of DOI:10.1016/0022-328X(86)80299-6

The one-electron electrochemical reductive cleavage of (η⁶-fluorene)Cr(CO)3 gives the (η⁶-fluorenyl)Cr(CO)3 anion.This anion reacts at 0 deg C in DMF with benzyl chloride present in excess during electrolysis to give (9-exo-benzylfluorene)Cr(CO)3 stereoselectively in 64percent yield.At higher temperatures there is competing formation of the exo and endo isomers.The reaction of Cr(CO)6 with 9-benzylfluorene is neither stereoselective nor regioselective, and gives moderate yields of the exo and endo isomers (26 and 17percent, respectively).The one-electron reduction of the exo isomer generates the conjugate base which initiates the exo-endo transformation.In the presence of benzyl chloride, the base-catalyzed isomerization competes with a slow benzylation of the base, and (9,9'-dibenzylfluorene)Cr(CO)3 can be isolated.