A Novel Synthesis of Dithieno[2,3-b:3′,2′-d]thiophene and its Bromo Derivatives

Abstract

D i t h i e n o [ 2 , 3 -b : 3 & ce nt;,2¢-d ] t h i o p h e n e a n d I t s B r o m o D e r i v a t i v e sAbstract: Two new approaches to multigram synthesis of dithieno[2,3-b:3¢,2¢-d]thiophene are described. Various mono-, di-, tri-and tetrabromides of dithieno [2,3-b:3¢,2¢-d]thiophene are prepared in good yield.Isomeric dithienophenes have received considerable attention as building blocks for the preparation of conjugated oligomers and polymers with potential use as organic conductors, 1 semiconductors, 2 photosensitive materials 3 and light emitting devices. 4 Out of six possible isomeric dithienophenes only dithieno[2,3-b:2′,3′-d]thiophene has been thoroughly studied while others isomeric dithienothiothenes have been rarely described. For instance, there are no examples of polymeric materials containing dithieno[2,3-b:3′,2′-d]thiophene as a monomeric unit and the chemistry of this compound is under-investigated. We believe that this is due to the lack of an efficient synthesis of dithieno[2,3-b:3′,2′-d]thiophene that permits preparation of this compound in significant amounts.The first synthesis of dithieno[2,3-b:3′,2′-d]thiophene was achieved by electrophilic cyclization of 2:5-bis-wdimethoxyethylmercaptothiophene in polyphosphoric acid (PPA), however the target compound was isolated in very low yield. 5 An alternative method based on oxidative ring closure of 3,3′-dilithio-2,2′-dithienyl sulfide, 6 3,3′-diZnCl or 3,3′-diCuCN derivatives 7 using CuCl 2 as an oxidation reagent was described. The required 3,3′-dibromo-2,2′-dithienyl sulfide was synthesized from 2-lithio-3-bromothiophene by treatment with dibenzenesulfonyl sulfide. Recently, Pd-catalyzed cross-coupling transformation of 3,3′-dibromo-2,2′-dithienyl sulfide to dithieno[2,3-b:3′,2′-d]thiophene was reported. However, this method requires high loading (20%) of Pd catalyst. 8Herein we describe two new convenient methods for large scale preparation of dithieno[2,3-b:3′,2′-d]thiophene (1) starting from thiophene or simple commercially available thiophene derivatives. The first strategy involved cyclization of 3,3′-dibromo-2,2′-dithienyl sulfide 2 as a key step. The second approach includes formation of the third thiophene ring starting from 2,2¢-dibromo-3,3¢-bithienyl (3) (Scheme 1). Scheme 1Another aim of this work was synthesis of bromo-derivatives which are key starting materials for the preparation of various substituted dithieno[2,3-b:3′,2′-d]thiophenes via a cross-coupling route or Li-Br exchange followed by reaction with electrophiles.Following the literature procedure, 6,9 we tried to prepare 3,3′-dibromo-2,2′-dithienyl sulfide (2) starting from 3-bromothiophene (4) but in our hands the yield did not exceed 15% (Scheme 2). Scheme 2Varying the solvents (THF, Et 2 O) and temperature did not improve the yield of the sulfide 2. Probably the low yield of the product was effected by diisopropylamine but our attempt to use PhLi instead of LDA did not improve the yield. Also unsuccessful were attempts to prepare the target molecule from 2,3-dib...

Elucidation of π‐Conjugation Modes in Diarene‐Fused 1,2‐Dihydro‐1,2‐diborin Dianions

“…[16] For the synthesis of compound 2, 2,2'-dibromo-3,3'-bithiophene, which should be used immediately after purification because of its instability at room temperature, [17] was treated with nBuLi in toluene, followed by reaction with compound 5 to afford compound 2 as airand moisture-sensitive yellow crystals in 34 % yield. The diboron source, (Me 2 N)BrB À BBrA C H T U N G T R E N N U N G (NMe 2 ) (5), was synthesized according to a literature procedure.…”

“…The diboron source, (Me 2 N)BrB À BBrA C H T U N G T R E N N U N G (NMe 2 ) (5), was synthesized according to a literature procedure. [16] For the synthesis of compound 2, 2,2'-dibromo-3,3'-bithiophene, which should be used immediately after purification because of its instability at room temperature, [17] was treated with nBuLi in toluene, followed by reaction with compound 5 to afford compound 2 as airand moisture-sensitive yellow crystals in 34 % yield. The chemical reduction of compound 2 with excess KC 8 in tetrahydrofuran (THF) gave a dark-purple solution of the dianion (2 2À…”

Efficient Synthesis of Trimethylsilyl-Substituted Dithieno[2,3-b:3′,2′-d]thiophene, Tetra[2,3-thienylene] and Hexa[2,3-thienylene] from Substituted [3,3′]Bithiophenyl

“…In fact, direct conversion of compound 7 (step f, Scheme 1) gave compound 1 in much lower yield (31%) according to the literature. 12 In contrast, our method offers a practical route to compound 1 in reasonably good yields (overall 40-47%). Subsequent removal of the TMS groups in 9 in the presence of TFA generated the target compound 1 in 98% yield.…”

Chelated Fischer carbene complexes of annulated thiophenes: synthesis, structure and electrochemistry

“…Thiophene oligomers (and polymers) are widely studied because of their electroconductive and photonic properties. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Application of α-connected, conjugated thiophene units in chain stuctures 1,[5][6][7] and α,β-fused thiophene rings in band structures 1,2,4,[8][9][10][11][12] are finding wide application as organic conductors/superconductors 4,7,8 and non-linear optical materials. 1,5,6,9 In addition, oligothiophenes are appealing units to act as spacer-ligands between metal fragments for potential long distance metal-metal communication.…”