Palladium-catalyzed C-H arylation of electron-enriched heteroarenes with aryl bromides and aryl chlorides proceeds in the presence of LiO-t-Bu as a base. The reaction allows one-pot synthesis of differently substituted 2,5-diarylthiazole with the same catalyst system by switching the solvent and the amount of base.

Poly(3-hexylthiophene) was synthesized by the polycondensation of 2-bromo-3-hexylthiophene with a nickel catalyst and (2,2,6,6-tetramethylpiperidin-1-yl)magnesium. The polymerization proceeded at room temperature in a highly regioregular manner.Oligothiophenes and polythiophenes attract considerable attention in materials science. Regioregular polythiophene, which involves head-to-tail (HT) repeating unit such as poly(3-hexylthiophene) (HT-P3HT) (1) (Chart 1) is of particular interest since the compound shows remarkable physical properties materials such as organic TFTs, thin-film organic solar cells, and conductive polymers.1 Debrominative polycondensation of 2,5-dibromo-3-hexylthiophene (2a) with a Grignard reagent in the presence of a transition-metal catalyst is a method of choice for the preparation of 1.1d,2 A regiochemical error in the halogenmetal exchange causes incomplete conversion to the polymer 1. Although use of the 5-iodinated derivative 2b is a solution to such problem, 3 preparation of 2b requires multistep procedures as well as inferior atom efficiency. On the other hand, the dehydrobrominative method to afford 1 with 2-bromo-3-hexylthiophene (3) is a potentially atom-economic pathway. Deprotonation of 3 with lithium amide and following metal exchange with zinc 1d or magnesium 2a2f,3 also gives 1 although extremely low temperature is necessary. A palladium-catalyzed direct polycondensation in the presence of an alkali metal carbonate has recently been shown to lead to polymer, 4 however, high temperature is necessary to afford the polythiophene in a reasonable yield with high degree of polymerization. It is thus highly intriguing to develop milder dehydrobrominative polymerization (around room temperature), which would be a goal for the efficient preparation of regioregular polythiophenes. We envisaged that our recent efforts on the development of transition-metal-catalyzed CH functionalization of heteroaromatic compounds 5,6 can be applied to the synthesis of HT-P3HT (1) and herein disclose that the employment of Knochel-Hauser base 7 and a nickel-catalyst is a practical dehydrobrominative polycondensation method toward highly regioregular poly(3-substituted thiophene)s at room temperature with high atom efficiency.We first examined palladium-catalyzed polymerizaton of 3a in the presence of lithium t-butoxide. 8 The polymerization occurred at 50°C to afford the corresponding polymer 1 with M n of 7600. In contrast to the above undesired results, it was found that the use of (2,2,6,6-tetramethylpiperidin-1-yl)magnesium chloride¢LiCl (4), which was developed by Knochel for the proton abstraction of various sp 2 CH bonds, 7 induced polymerization highly efficiently. When the reaction was carried out with 0.5 mol % [NiCl 2 (dppe)] as catalyst, the corresponding HT-P3HT (1) was obtained in quantitative yield in contrast to debrominative polymerization with a Grignard reagent which does not reach complete conversion due to regiochemical error in the halogenmetal exchange. The obtained polymer 1 exh...

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p-Conjugated polymers are synthesized by C-H and C-X polycondensation of 2-(4-haloaryl)thiophene monomers with a nickel catalyst, and the Knochel-Hauser base (TMPMgCl . LiCl (chloromagnesium 2,2,6,6-tetramethylpiperidide lithium chloride salt)). The C-H functionalization polycondensation reaction of a monobrominated monomer undergoes dehydrobrominative polymerization with an equimolar amount of TMPMgCl . LiCl and a catalytic amount of NiCl 2 dppp to produce poly(2,5-thienylene-1,4-phenylene) and poly(2,5-thienylenepyridine-2,5-diyl) with reasonable yields. Polycondensation with triflate as a leaving group proceeds under similar conditions to produce poly(thienylenephenylene) with an excellent yield. Poly(benzodithiophene) was also obtained from the reaction of the corresponding monobrominated benzodithiophene in the presence of a nickel-catalyst-bearing N-heterocyclic carbene as a ligand.

The reaction allows an efficient access to various arylated heteroarenes including a one‐pot, two‐step synthesis of differently substituted 2,5‐diarylthiazoles.