Synthesis of [1]Benzothieno[2,3-b][1]benzothiophenes from 3-Arylbenzo[b]thiophenes through Iodine-Mediated Sulfur Insertion Reaction

Abstract

The reaction of 3-arylbenzo [b]thiophenes and elemental sulfur to obtain [1]benzothieno [2,3-b][1]benzothiophenes (BTBTs) is reported. The addition of molecular iodine is essential for the reaction. In previous reactions that used 1,1-diarylethylenes as the starting material, side products that were difficult to separate were generated. The present reaction does not produce such side products and is therefore advantageous for obtaining BTBTs in high yield and purity.

Synthesis of [1]Benzothieno[3,2‐b][1]benzothiophenes through Iodine‐Mediated Sulfur Insertion Reaction

“…First, we examined the reaction conditions for the synthesis of simplest BTBT 4 a using 2-phenylbenzo[b]thiophene 3 a as the model substrate (Table 1). We started with the reaction conditions that were optimized for the synthesis of 2 from 1 (Scheme 1) [3] and were able to obtain the expected product (entry 1). However, the NMR yield was only 20 %.…”

“…[1] We have recently developed a novel synthetic method to obtain [1]benzothieno[2, 3-b][1]benzothiophenes 2 [2] from 3arylbenzo[b]thiophenes 1 (Scheme 1, top). [3] The advantage of the method lies in its simplicity, where 1 and elemental sulfur [4] are heated in toluene in air in the presence of molecular iodine. [5] However, in the field of OFETs, [1]benzothieno [3,2b][1]benzothiophenes (BTBTs) 4 that do not have cross-conjugated systems have received far more attention than 2.…”

A Review on the Synthetic Methods towards Benzothienobenzothiophenes

“…Observing that 3-aryl benzothiophene 8 was the intermediate formed during the synthesis of the benzothieno [2,3b]benzothiophene motif from 88, the same authors introduced a methodology starting from 3-aryl benzothiophene for the synthesis of these heteroacenes. [50] By treating 3-phenyl benzothiophene 8 with sulfur and iodine in toluene at 110 °C for 48 h, the authors could isolate benzothieno [2,3b]benzothiophene 2a in 76 % yield (Scheme 32). The generality of the method was studied carefully and 12 examples of benzothieno [2,3-b]benzothiophenes were synthesized in moderate to good yields starting from appropriately substituted 3aryl benzothiophenes.…”

“…The authors proposed a mechanism for the iodine mediated synthesis of benzothieno [2,3-b]benzothiophene starting with the formation of sulfur diiodide (IÀ SÀ SÀ S n À I) from the reaction of sulfur and iodine (Scheme 33). [50] Then, a nucleophilic addition from the C2 position of In the report by Knochel and co-workers which was discussed in the previous section, four examples of benzothieno [2,3-b]benzothiophene analogues were also synthesized by following the multistep synthetic route (Scheme 34). [51] , resulting in an 80 % yield of benzothienyl dithiocarbamates 96.…”

Direct Synthesis of Benzoselenophene and Benzothiophene Derivatives from 1,1-Diarylethenes and Biaryls by Chalcogen Cation-Mediated Successive Bond Formation

“…Some additional observations should be noted: other halogenated solvents such as DCM and DCE were also effective, but TCE was the best for transforming 1a into doubly cyclized product 2a convergently. A combined use of Se powder with TMSCN or I 2 gave a much smaller amount of singly cyclized product 2a′ [<16% (see the Supporting Information for more detailed optimization studies)].…”