Efficient Synthesis of a Regioregular Oligothiophene Photovoltaic Dye Molecule, MK‐2, and Related Compounds: A Cooperative Hypervalent Iodine and Metal‐Catalyzed Synthetic Route

Abstract

We have successfully established an efficient route to the core structure of donor-acceptor head-to-tail (H-T)-linked regioregular oligothiophenes, which includes the following key synthetic steps, that is, hypervalent iodine induced direct and regioselective coupling of thiophenes and the use of the obtained bithiophenes as excellent coupling substrates for the Suzuki and Stille couplings. The versatility of this new approach is highlighted in the dramatic improvement of the yield (ca. 59 % overall yield) of MK-2, a high-performance organic dye, for photovoltaic applications.

Pioneering Metal‐Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents

“…Therefore, our unique H–T bithiophene synthesis based on the involvement of the iodonium salts 53 was further applied for the concise syntheses of the efficient photovoltaic donor–acceptor oligothiophene MK‐2, a high‐performance organic dye, and related artificial molecules for utilization in solar cells with dramatically improved yields (Scheme , seven synthetic steps, ca. 59% overall yield) compared to known approaches. The synthetic route includes utilizing H–T bithiophene 55 obtainable by the hypervalent iodine regioselective coupling as an excellent substrate for the subsequent Suzuki and Stille couplings as the key steps for accessing the regioregular H–T‐linked quaterthiophene 56 carrying the donor carbazole group.…”

“…When evaluating the low toxicity, these hypervalent iodine(III) reagents are now considered some of the most effective oxidants to reproduce the oxidation processes, and these methods were widely used for the total synthesis of an extensive series of natural products having important biological properties . This second success story also motivated us to develop the pioneering hypervalent iodine chemistry in organic synthesis for 30 years …”

“…For these accomplishments, we would like to now provide in this Personal Account a scholarly presentation of our strategies and developments in the metal‐free oxidative coupling methods of aromatic compounds using hypervalent iodine reagents, starting from our first discovery of the SET oxidation process for activating aromatic rings.…”

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

“…Syntheses of (3HT) 3 , phosphine ligands, and their precursors were based on previously reported procedures (–S , Supporting Information) . Synthesis and isolation of catalysts for characterization were carried out using NiCl 2 hexahydrate to simplify purification procedures.…”

Heteroaryliodonium(III) Salts as Highly Reactive Electrophiles

“…The reaction proceeded through the in-situ formation of thienyliodonium salt 42 from an electron-rich thiopene and Koser's reagent in hexafluoroisopropanol (HFIP). It was proposed that the intermediate thienyliodonium species was activated by the addition of trimethylsilyl bromide, followed by its coupling with electron-rich arenes to provide a wide range of useful mixed biaryl products 43 (Kita et al, 2009(Kita et al, , 2011Morimoto et al, 2010Morimoto et al, , 2011Dohi et al, 2013) (Figure 2C, Equation h). In 2013, Gaunt et al developed a new acyl coupling reaction that merges the aryl transfer ability of diaryliodonium salts with carbonyl umpolung using an N-heterocyclic carbene (NHC) catalyst 44.…”