Cul/HMPA-catalyzed Alkylation to Tolan: a Valuable Method for Discotic Liquid Crystal Hexabenzocoronene

摘要

In this paper, a novel protocol of akylation to tolan using CuI/HMPA as catalyst for synthesizing alkyl-substituted hexabenzocoronene (HBC) was described. The key step in the route was the construction of tolan bearing 2 long side chains, which was completed in the first step via coupling reaction between 4, 4'-Bis(bromomethyl)tolan (1) and Grignard Reagent in a mild condition. Afterward, Co_2(CO)_8 catalyzed cyclotrimerization gave hexaphenylbenzene derivative (HPB) which could be easily separated by column chromatography and recrystalization. The planarization of HPB was carried out with FeCl_3 /MeNO_2 to afford the desired HBC with long odd-carbon alkyl chains in good overall yields.