The biaryl structure is a common feature in many compounds of technological and pharmaceutical relevance, and it has been studied comprehensively in recent years to find innovative and more cost-effective methods for the formation of aryl-aryl bonds.
Generally aryl C-C bond formation is facilitated by a transition metal catalyst, typically Palladium, which couples two aryl groups functionalized respectively with a leaving group (I, Br) and an organometallic moiety (-B(OR)2, -SnR3, -ZnR, -MgX). However, functionalization with the latter groups requires extra synthetic steps and the compounds are often unstable or toxic .
Direct heteroarylation, instead, does not need an organometallic moiety, but it involves the coupling of an arene with a leaving group with an arene C-H bond. The main drawback is represented by the use of harmful solvents (e.g. DMA, DMF). Recently, new and more environmentally friendly protocols for direct arylation have been explored, they include use of more sustainable solvents such as water , ionic liquids, or even in absence of solvent [4,5].
The use of an IR lamp as a heating source has proved to be a good alternative to conventional ones: it has been employed to reduce reaction time and improve product yields .
This study fits into this frame and shows the first example of infrared assisted solvent-free direct arylation is presented: this protocol makes it possible to achieve high yields in a short time, avoiding the formation of unwanted by products and making workup easier. In particular, the coupling of thieno[3,4-c]pyrrole-4,6-dione with electron-rich and electron-poor aryl iodides has been successfully carried on, affording yields as high as 77% in just one hour reaction.