Ken-ichiro Kanno

Recent development for formation of aromatic compounds via metallacyclopentadienes as metal-containing heterocycles

Metallacyclopentadiene, which is recognized as a metal-containing heterocycle, is an important intermediate for the formation of aromatic derivatives. In this short review, we summarized the recent advance in selective aromatic compounds formation catalyzed or mediated by transition metal complexes via metallacyclopentadienes which are formed by intermolecular coupling of various alkynes including unsymmetrical alkynes, two different alkynes and three different alkynes. Some reaction mechanisms were also reviewed.

Zirconium-mediated coupling reaction for synthesis of substituted thiophene-fused acenes.

A novel zirconium-mediated synthesis of substituted thiophene-fused acenes is described. A variety of substituents, such as alkyl, aryl, silyl, iodo, and alkynyl groups, could be introduced to the acene skeleton by this method. Moreover, the double coupling with tetraiodothiophene gave the corresponding dianthrathiophene.

Zirconium-mediated selective synthesis of 1,2,4,5-tetrasubstituted benzenes from two silyl-substituted alkynes and one internal alkyne.

Selective synthesis of 1,2,4,5-tetrasubstituted benzenes was achieved via formation of 2,5-bis(trimethylsilyl)zirconacyclopentadienes from 2 equiv of TMS-substituted alkynes with Cp(2)ZrBu(2) and Cu-mediated formation of 1,4-disilylbenzene by cycloaddition of zirconacyclopentadienes to disubstituted alkynes. Preparation of 1,2,3,4,9,10-hexasubstituted pentacene and 2,3,6,11-tetrasubstituted naphthacene derivatives were demonstrated by a homologation or coupling method using tetrasubstituted benzene.

Coupling of the R−Cp or Indenyl Ligand with the Diene Moiety of Bis(substituted cyclopentadienyl)- or Bis(indenyl)zirconacyclopentadienes

When bis(substituted cyclopentadienyl)- or bis(indenyl)zirconacyclopentadienes were treated with TiCl(4), a coupling reaction between the substituted cyclopentadienyl or indenyl ligand and the diene moiety proceeded to give indene or fluorene derivatives in moderate to high yields. With the sterically hindered t-Bu-substituted Cp ligand, the coupling products were obtained in high yields.

Double homologation method for substituted soluble pentacenes and dimerization behaviours of pentacenes.

Double up: A zirconium-mediated double homologation method was successfully applied for the synthesis of multi-substituted pentacene derivatives from 1,2,4,5-tetrakis(propargyl)benzenes. The bis(zirconacyclopentadiene) intermediates were also characterized. Among these symmetrical derivatives, tetra- and octa-substituted pentacenes undergo reversible conversion between monomeric and dimeric forms. A double homologation method for the formation of substituted soluble pentacenes was developed by a zirconium-mediated cyclization of tetrayne derivatives. Thermal dimerization of tetra- and octasubstituted pentacenes was observed. The dimerization behavior was observed to be strongly related to the substituent groups affixed to the pentacenes.

Once Cleaved C-C Bond Was Reformed: Reversible C-C Bond Cleavage of Dihydroindenyltitanium Complexes

The once cleaved carbon-carbon bond of the Cp moiety in 2 was recombined in indene products. Aslo, we propose a novel mechanism for the cleavage of the carbon-carbon bond of the Cp moiety.

Selective Linear Triene Formation from Different Alkynes using Zr/Cu system

Selective synthesis of linear trienes from three different alkynes was achieved in one-pot procedure using the Zr/Cu system. Zirconacyclopentadiene prepared from two different alkynes such as an alkyl-substituted alkyne and an aryl-substituted alkyne reacted with NCS gave chlorodienylzirconocene. It reacted with the third alkyne with electron-withdrawing groups in the presence of CuCl to afford the corresponding linear triene.

Preparation of 6,13-Bis(trimethylsilyl)pentacene and Formation of Second-Ring Diels−Alder Adduct of Pentacene

6,13-Bis(trimethylsilyl)pentacene was synthesized by a coupling reaction of bicyclic dilithiobutadiene with diiodonaphthalene followed by aromatization. Diels-Alder reaction of 6,13-bis(trimethylsilyl)pentacene with dienophiles afforded the corresponding second-ring adducts. Elimination of two silyl groups gave the second-ring Diels-Alder adducts of parent pentacene.

Synthesis of 1,2,3,4,8,9,10,11-octasubstituted pentacenequinone derivatives and their conversion into substituted pentacenes.

A series of 1,2,3,4,8,9,10,11-octasubstituted pentacenequinone derivatives were prepared by the oxidation of 1,2,3,4,8,9,10,11-octasubstituted pentacenes, which were synthesized by the double homologation method. Oxidation of the pentacenes was carried out with H(5)IO(6) or air and DDQ. These octasubstituted pentacenequinones were converted into 1,2,3,4,6,8,9,10,11,13-decasubstituted or 2,3,6,9,10,13-hexasubstituted pentacene derivatives by the introduction of aryl or alkynyl groups at the carbonyl carbons. The photophysical properties of these new pentacenes have been measured in solution, and the substituent effects are discussed.