Atsushi Sugie

C–H Functionalization Polycondensation of Chlorothiophenes in the Presence of Nickel Catalyst with Stoichiometric or Catalytically Generated Magnesium Amide

Polymerization of 2-chloro-3-substituted thiophenes proceeded with a stoichiometric amount of magnesium amide, TMPMgCl·LiCl, or a combination of a Grignard reagent and a catalytic amount of secondary amine in the presence of a nickel catalyst. Although the nickel-catalyzed polymerization with NiCl(2)dppe, which exhibited high catalytic activity in the reaction of bromothiophenes, was less effective, use of a nickel catalyst bearing N-heterocyclic carbene as a ligand was found to induce polymerization with controlled molecular weight and molecular weight distribution.

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.

Stepwise construction of head-to-tail-type oligothiophenes via iterative palladium-catalyzed CH arylation and halogen exchange.

The well-defined head-to-tail oligothiophenes were synthesized via palladium-catalyzed CH arylation and halogen exchange sequentially through the 2-halothiophene derivatives.

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 n-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.

Concise Synthesis of Well-Defined Linear and Branched Oligothiophenes with Nickel-Catalyzed Regiocontrolled Cross-Coupling of 3-Substituted Thiophenes by Catalytically Generated Magnesium Amide

The synthesis of linear and branched oligothiophenes of well-defined structures is performed with regioselective deprotonation of 3-substituted thiophenes and nickel-catalyzed cross-coupling of the thus formed metalated species with a bromothiophene. The reaction of 3-hexylthiophene with EtMgCl and 2,2,6,6-tetramethylpiperidine (TMP-H, 10 mol%) induces the metalation selectively at the 5-position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2-halo-3-hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head-to-tail (HT)-type dimer. By repeating the same sequence, the linear oligothiophene up to a 4-mer is synthesized in good yield. The reaction of 3-hexylthiophene with 2,3-dibromothiophene also takes place to afford a branched oligothiophene 3-mer in quantitative yield. The obtained 3-mer is also metalated at the sterically less-hindered position in a regioselective manner furnishing a 7-mer in >99% yield after a further coupling reaction with 2,3-dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes.

Iterative extension of thiophene ring leading to head-to-tail-type oligothiophenes via stepwise CH arylation and halogen exchange sequence

Iterative extension of the thiophene ring unit leads to oligothiophenes. The coupling reaction at the CH bond of thiophene with halo-thiophene occurs at the 5-position of 2-bromothiophene with 2-iodothiophene in the presence of a palladium catalyst and AgN0 3 /KF as an activator to give the corresponding bithiophene, whose carbon-bromine bond remains. Halogen exchange converts the bromine atom to iodide, which also allows further reaction to form thiophene-thiophene bond. Oligothiophenes are obtained by repeating such sequense.

PALLADIUM-CATALYZED ARYLATION AT C-H AND C-C BONDS OF MASKED THIAZOLE DERIVATIVES

The differently substituted 2,5-diarylthiazole derivatives are synthesized via palladium catalyzed sequential C-H arylation at the 5-position and C-C bond activation at the 2-positon with masked thiazole.

C-H ARYLATION OF 3-SUBSTITUTED THIOPHENE WITH REGIOSELECTIVE DEPROTONATION BY TMPMgCl·LiCl AND TRANSITION METAL CATALYZED CROSS COUPLING ‡

Abstract – The reaction of 3-hexylthiophene with Knochel-Hauser base (TMPMgCl·LiCl) induced the metalation at the 5-position of the thiophene ring selectively. Following addition of several aryl halides in the presence of a nickel or palladium catalyst afforded regioselectively arylated thiophene in good to excellent yields. INTRODUCTION CH functionalization of heteroaromatic compounds recently attracts much attention 1,2 since a variety of organic compounds bearing heteroaromatic moiety in the structure are found in a wide range of advanced organic materials 3 as well as biologically active molecules. 4 Therefore, development of a practical synthetic strategy for such molecules is an important issue in organic synthesis. We have been engaged in the development of synthetic methodologies to afford functionalized heteroaromotics via transition metal catalyzed CH functionalization. 5 Several functionalization reactions, which take place at a carbon atom of an electron-deficient 6 and enriched

STRUCTURAL DIVERSITY OF THE WHEAT NUCLEAR GENE WAOX1a ENCODING MITOCHONDRIAL ALTERNATIVE OXIDASE, A SINGLE UNIQUE ENZYME IN THE CYANIDE- RESISTANT ALTERNATIVE PATHWAY

ABSTRACT Alternative respiratory pathways other than the main cytochrome pathway are present in plant mitochondria, one of which is represented by a single unique enzyme alternative oxidase (AOX). Two genes encoding AOX proteins in common wheat have already been characterized (24). To further understand the structural diversity of the Aox genes in wheat, we screened the common wheat genome library for additional members of this small multigene family. Twelve Aox-related sequences were detected by Southern blot and restriction analyses and four of them were successfully subcloned and sequenced. All of the newly isolated sequences appear to be more closely related to the wheat gene Waox1a than Waox1c. Structural analysis showed that one clone was identical to Waox1a and three others appeared to be non-functional as they contained insertion/deletion mutations and/or frame-shift mutations leading to in-frame stop codons on different locations. In addition, one genomic clone highly homologous to the Waox1a cDNA sequence was identified. This cDNA-like sequence was also identified in the genomes of diploid, tetraploid and hexaploid wheat accessions. Although its origin remained unknown, our result indicated that it evolved before divergence of the ancestral wheat genomes.