Evidence for rhenaphenanthrene formation and its conversion to fluorenone

Article abstract of DOI:10.1021/om00097a001

Introduction of 2,2′-dilithiobiphenyl to PPh₃(CO)₄ReBr gives 9-fluorenone. 9-Fluorenone may be formed via a reductive elimination from a rhenaphenanthrene intermediate. Reaction of 2,2′-dilithiobiphenyl with (CO)₅ReBr also gives 9-fluorenone. A mechanism consistent with this conversion involves formation of a rhenacycloheptatetraene followed by ring contraction to the rhenaphenanthrene 4. Reductive elimination from 3 gives the product. Reaction of 2,2′-dilithiobiphenyl with (CO)₅ReBr followed by low-temperature oxidative quenching generates 9,10-phenanthrenequinone and 9-fluorenone. Isolation of 9,10-phenanthrenequinone supports the mechanistic route that incorporates the rhenacycloheptatetraene intermediate.