An intramolecular arene-triflate coupling reaction for the regiospecific synthesis of substituted benzofluoranthenes

Abstract

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 yield when performed using 0.1 equiv of the palladium catalyst, 3 equiv of lithium chloride, and 1.2 equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene in N,N-dimethylformamide at 140 o C. The biaryl precursors needed for the coupling reaction can be prepared by [1,2-bis(diphenylphosphino)ethane]nickel (II) choride catalyzed coupling of an aryl bromide with an [o-(methoxymethoxy)aryl]magnesium bromide (prepared by ortho-lithiation of an aryl methoxymethyl ether followed by transmetalation with magnesium bromide). Using this procedure benzo[a]fluoranthene, benzo[b]fluoranthene, benzo[j]fluoranthene, and benzo[k]fluoranthene were prepared in yields of 84%, 85%, 93%, and 64%, respectively.