An Intramolecular Arene-Triflate Coupling Reaction for the Regiospecific Synthesis of Substituted Benzofluoranthenes

Article abstract of DOI:10.1021/jo00058a023

An intramolecular triflate-arene coupling reaction mediated by bis(triphenylphosphine)palladium(II) chloride has been developed for the synthesis of each of the isomeric benzofluoranthenes.This reaction, which results in formation of a new five-membered ring, proceeds in highest yields when performed using 0.1 equiv of the palladium catalyst, 3 eqiv of lithium chloride, and 1.2 eqiv of 1,8-diazabicyclo<5.4.0>undec-7-ene in N,N-dimethylformamide at 140 deg C.The biaryl precursors needed for the coupling reaction can be prepared by <1,2-bis(diphenylphosphino)ethane>nickel(II) chloride catalyzed coupling of an aryl bromide with an magnesium bromide (prepared by ortho-lithiation of an aryl methoxymethyl ether followed by transmetalation with magnesium bromide).Using this procedure benzofluoranthene, benzofluoranthene, benzofluoranthene, and benzofluoranthene were prepared in yields of 84percent, 85percent, 93percent and 64percent, respectively.The reaction to prepare benzofluoranthene was regiospecific and afforded none of the six-membered ring product, perylene.This method was extended to the preparation of benzofluoranthene (BbF) derivatives with fluoro or methoxy groups on the benzo ring.The cyclization of compounds posessing a methoxy group on the same ring as the triflate required the addition of 0.4 equiv of triphenylphosphine to the reaction mixture.Strategies are reported for the regiospecific preparation of 4-, 5-, 6-, and 7-substituted benzofluoranthenes.Evidence is presented wich suggests the intermediacy of radicals in the oxidative-addition of aryl triflates to the palladium catalyst.