Radical-Cascade Avenue for 3,4-Fused-Ring-Substituted Thiophenes

Abstract

A single-step intramolecular radical cascade reaction of diynes and thioacetic acid in the presence of a catalytic amount of azobis(isobutyronitrile) as a radical initiator has been developed to synthesize thiophenes. This method allows easy and effective construction of a thiophene scaffold having 3,4-fused-ring substitution and unsubstituted 2,5-positions for further functionalization and polymerization. Using this method, derivatives of cyclopenta[ c]thiophene, 3,4-ethylenedioxythiophene, and thiophene-containing spirocyclic compound have been synthesized.

Mechanisms of Ssp3–H functionalization of thiolacetic acid: A density functional theory investigation

“…From the analysis of Figure 1B,D,F, it shows that single electron would transfer from C atom of IM1 to S6 atom of IM3. According to Agrawal et al [ 18 ] and our computational results, it found that the radical intermediate IM8 could also be yielded in the process from IM5 toP via SN2 reaction in Scheme 4. So in the Path 2, radical IM8 reacts with CH 3 COSH to generate IM3 via transition state TS3.…”

“…Based on Agrawal et al, [ 18 ] thiolacetic acid (CH 3 COSH) would go through a Ssp 3 –H activation process, which could convert diyne into cyclopenta[ c ]thiophene and its derivatives in the solvent of toluene at the temperature of 80°C in Scheme 2. Firstly, AIBN initiator would go through a homolytic reaction to generate the radical IM1, which could convert CH 3 COSH into thiyl radical via two Ssp 3 –H activation paths; then diynes (R1, ···, R11) as the reactants could interact with thiyl radical to yield a series of products.…”

“…However, both these two methods not only are multistep reactions but also need metal catalysts. Inspired by these reactions, Kumar and his coworkers employed azodiisobutyronitrile (AIBN) as radical initiator to convert diyne and its derivatives into 3,4‐fused‐ring‐substituted thiophene via Ssp 3 –H activation of thiolacetic acid in Scheme 2, [ 18 ] which could avoid the complex reaction steps, harsh reaction conditions, and environmental pollution. The proposed mechanism was described in Scheme 4.…”

Synthesis and Structural Study of 4H‐Cyclopenta[c]thiophene‐5,5(6H)‐dicarbonitrile and 6,6‐Dimethyl‐1,4‐dihydro‐5H‐cyclopenta[d][1,2]dithiine‐5,7(6H)‐dione

“…Pioneer work regarding the synthesis of different CPT and their application in OFETs has been reported later by Y. Aso et al . and Zade et al . In recent years, synthesis of 2,5‐disubstituted CPT from various substrates of diverse functionality was repoted by Yamamoto et al .…”

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates

“…Indeed, this is one of the few examples of a diyne cyclization via thiyl radicals that one can find in the literature. A second account of diyne reactivity under thiyl radical addition appeared three decades later, in which Agrawal et al optimized a number of substrates with malonate-type backbones for cyclization to the respective thiophene [35]. This approach relies on thermolysis of AIBN in toluene with thioacetic acid as the acyl thiyl radical source, and furnished a number of the bicyclic thiophenes, in good yield.…”