Deprotonative Metallation of Benzofuran and Benzothiophene Derivatives for the Formation of Tetracyclic and Pentacyclic Heteroaromatic Compounds

Abstract

N,N‐dialkylbenzofuran‐ and N,N‐dialkylbenzothiophene‐2‐carboxamides were readily prepared from bare benzofuran and benzothiophene by deprotocupration followed by trapping with N,N‐dialkylcarbamoyl chlorides. They were reacted with 2‐benzofuryl‐ and 2‐benzothienyllithiums to form symmetrical and unsymmetrical diarylketones, or underwent deprotolithiation‐electrophilic trapping sequences at their 3 position. From 3‐iodinated derivatives, copper‐catalysed N‐arylation of azoles was performed, followed by lithium amide‐promoted cyclisation, to give ‘tripentone’ analogues. The diarylketones were also iodinated at their 3,3’ positions and then engaged in the copper‐promoted double N‐arylation of anilines, giving rise to a family of original pentacyclic derivatives. A preliminary assessment of their electrochemical and biological properties was carried out, showing promising results against the proliferation of melanoma cells.