Kiyohiko Nakajima

Palladium-Catalyzed Synthesis of Endocyclic Allenes and Their Application in Stereoselective [2 + 2]Cycloaddition with Ketenes

Palladium-catalyzed reactions of various 2-bromo-3-exo-methylenecycloalkenes with a stabilized nucleophile were examined. When the carbocycles were nine-membered or larger, the corresponding endocyclic allenes were isolated in excellent yields. In a reaction of the eight-membered cyclic substrate, initial formation of a cycloocta-1,2-diene derivative was detected; however, it dimerized slowly. The seven-membered carbocycle was inert to the reaction. Using a chiral Pd-catalyst, an axially chiral endocyclic allene was obtained in 65% ee. The cyclic allenes were applied to [2 + 2]cycloaddition with ketenes, and the stereoselectivity was studied.

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.

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.

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.

Formation of cyclooctatetraenes from zirconacyclopentadienes

Treatment of zirconacyclopentadienes with 2 equiv. of CuCl at room temperature and with 1 equiv. of NBS at –78 °C selectively afforded cyclooctatetraene derivatives in good yields.

Reductive elimination of α-alkynyl substituted zirconacyclopentenes: formation of cyclobutene derivatives

Reductive elimination of α-alkynyl substituted zirconacyclopentenes, prepared from diaryldiynes and Cp2ZrEt2, proceeded upon heating or in the presence of dimethyl acetylenedicarboxylate to give alkynylcyclobutene derivatives.