Synthesis of Thieno[3,2‑<i>b</i>]indoles via Halogen Dance and Ligand-Controlled One-Pot Sequential Coupling Reaction

A two-pot synthesis of thieno­[3,2-<i>b</i>]­indole from 2,5-dibromothiophene is described. A halogen dance of 2,5-dibromothiophene was performed with LDA, and subsequent Negishi coupling was performed with 2-iodoaniline derivatives to provide the corresponding coupling products. The resulting two bromo groups have different reactivities, which were utilized for the one-pot Suzuki–Miyaura coupling/intramolecular Buchwald–Hartwig amination to produce thieno­[3,2-<i>b</i>]­indole via an assisted tandem catalysis that involved in situ ligand exchange

Nickel(II)-Catalyzed Cross-Coupling Polycondensation of Thiophenes via C–S Bond Cleavage

Cross-coupling polycondensation of thiophene derivatives occurs via C–S bond cleavage in the presence of a nickel catalyst. Head to tail type (HT) regioregular poly­(3-hexylthiophene) is obtained by a nickel­(II)-catalyzed deprotonative C–H functionalization polycondensation of 2-(phenylsulfonyl)-3-hexylthiophene with stoichiometric TMPMgCl·LiCl or with the catalytic secondary amine/RMgX. Debrominative Grignard metathesis (GRIM) polymerization with 5-bromo-2-(phenylsulfonyl)-3-hexylthiophene also proceeds by the catalysis of the nickel­(II) complex to afford the corresponding polythiophene

Synthesis of Well-Defined Head-to-Tail-Type Oligothiophenes by Regioselective Deprotonation of 3-Substituted Thiophenes and Nickel-Catalyzed Cross-Coupling Reaction

Iterative growth of thiophene oligomers by single-step extensions has been realized by regioselective metalation of 3-substituted thiophenes with the Knochel–Hauser base (TMPMgCl·LiCl) and coupling with bromothiophene using a nickel catalyst. Treatment of 3-hexylthiophene with TMPMgCl·LiCl induces metalation at the 5-position selectively. Subsequent addition of 2-bromo-3-hexylthiophene and a nickel catalyst leads to the corresponding bithiophene. The obtained bithiophene is converted to the terthiophene and then to the quaterthiophene by repeating the similar protocol. A concise synthesis of MK-1 and MK-2, which are organic dye molecules bearing an oligothiophene moiety that are used in photovoltaic cells, has been achieved

Murahashi Coupling Polymerization: Nickel(II)–N-Heterocyclic Carbene Complex-Catalyzed Polycondensation of Organolithium Species of (Hetero)arenes

Revisiting Murahashi coupling, we found that it effectively allows polymerization of lithiated (hetero)­arenes by nickel­(II)-catalyzed polycondensation. Deprotonative polymerization of 2-chloro-3-substituted thiophene with <i>n</i>-butyllithium gave head-to-tail-type poly­(3-substituted thiophene). Poly­(1,4-arylene)­s were obtained by the reaction of the corresponding dibromides through lithium–bromine exchange. A lithiated thiophene derivative obtained via deprotonative halogen dance also underwent polymerization to afford a bromo-substituted polythiophene

Studies on the Generation of Metalating Species Equivalent to the Knochel–Hauser Base in the Dehydrobrominative Polymerization of Thiophene Derivatives

Dehydrobrominative polycondensation of 2-bromo-3-hexylthiophene proceeded with TMPMgBr·LiBr and (TMP)₂Mg·2LiBr, formed by LiTMP and MgBr₂, which was found to serve as a surrogate of the Knochel–Hauser base TMPMgCl·LiCl, and head-to-tail-type regioregular poly­(3-hexylthiophene) was obtained with high efficiency. The regioregular poly­(3-hexylthiophene) was also found to be obtained by one-shot addition of 2-bromo-3-hexylthiophene as a monomer, magnesium amide, and a nickel catalyst, suggesting that complete formation of metalated thiophene species is not an essential requisite for the successful polymerization with a nickel catalyst. This method was employed for the preparation of tolyl-terminated polythiophene by an aryl group with narrow molecular weight distribution using (<i>o</i>-tolyl)­NiCldppp as a catalyst

Axially Chiral Macrocyclic <i>E</i>-Alkene Bearing Bisazole Component Formed by Sequential C–H Homocoupling and Ring-Closing Metathesis

Clipping by ring-closing metathesis freezes rotation of a C–C bond to result in forming axial chirality. Treatment of bisbenzimidazole bearing an <i>N</i>-(3-butenyl) substituent with a Grubbs’ catalyst undergoes ring-closing metathesis, in which the stereochemistry of the thus formed olefin was exclusively <i>E</i>-form. Analysis by HPLC with a chiral stationary column confirmed clear baseline separation of each enantiomer

Synthesis of Oligo(thienylene-vinylene) by Regiocontrolled Deprotonative Cross-Coupling

Concise synthesis of oligo­(thienylene-vinylene) with a head-to-tail type structure is achieved by regioselective deprotonative coupling of 3-hexylthiophene. The palladium catalyzed reaction of 3-hexylthiophene with (<i>E</i>)-2-(2-bromoethenyl)-3-hexyl­thiophene takes place to afford head-to-tail type <i>trans</i>-1,2-dithienyl­ethene. Further extension of a vinylthiophene unit is similarly performed in an iterative manner

Synthesis of Poly(3-substituted thiophene)s of Remarkably High Solubility in Hydrocarbon via Nickel-Catalyzed Deprotonative Cross-Coupling Polycondensation

Polythiophenes bearing a siloxane moiety in a substituent at the 3-position are prepared by deprotonative polycondensation of 2-bromo-3-substituted-thiophene with a bulky magnesium amide chloromagnesium 2,2,6,6-tetramethyl­piperidine-1-yl lithium chloride salt (TMPMgCl·LiCl) catalyzed by a nickel complex. Deprotonation takes place at 60 °C for 1 h to form the corresponding thiophene magnesium species, which is subjected to the polymerization by addition of 0.1–5 mol % NiCl₂(PPh₃)­IPr (IPr: 1,3-bis­(2,6-diisopropyl­phenyl)­imidazole-2-yl). Polymerization proceeds in a highly regioregular manner, and the molecular weight of the thus-obtained polymer is controllable by the ratio of monomer feed/catalyst loading to indicate <i>M</i>_n of up to 280 000 with narrow molecular weight distribution. Chloro­thiophenes are also found to induce polymerization in a deprotonative manner with TMPMgCl·LiCl or <i>n</i>BuLi (the Murahashi coupling polymerization). The obtained polymers bearing a siloxane moiety in the substituent is revealed to be dissolved in a hydrocarbon allowing formation of thin film from hexane