The molybdenum-catalyzed asymmetric ring-closing metathesis of the various C_s-symmetric (π-arene)chromium substrates provides the corresponding bridged planar-chiral (π-arene)chromium complexes in excellent yields with up to >99 % ee. With a bulky and unsymmetrical substituent, such as N-indolyl or 1-naphthyl, at the 2-positions of the η⁶-1,3-diisopropenylbenzene ligands, both biaryl-based axial chirality and π-arene-based planar chirality are simultaneously induced in the products. The axial chirality is retained even after the removal of the dicarbonylchromium fragment, and the chiral biaryl/heterobiaryl compounds are obtained with complete retention of the enantiopurity.

Titanacyclopentadienes, prepared from [Cp₂TiBu₂] and either two equivalents of an alkyne or a diyne, were treated with PMe₃ (3 equiv) at 50 °C for 3 h and then with azobenzene at room temperature for 12 h to give 4,5,6-trisubstituted indene derivatives with the loss of one substituent in good yields. This reaction contrasts sharply with our previously reported reaction for the formation of 4,5,6,7-tetrasubstituted indene derivatives without the loss of substituents by the treatment of titanacyclopentadienes with azobenzene without PMe₃. ¹³C NMR spectroscopy of the product derived from a ¹³C-enriched complex revealed that the five carbon atoms originating from a Cp ligand were arranged linearly in the trisubstituted indene derivatives, in contrast to the 4,5,6,7-tetrasubsituted indene derivatives, in which the corresponding five carbon atoms are arranged in a ring.

Titanacyclopentadienes, prepared from [Cp₂TiBu₂] and either two equivalents of an alkyne or a diyne, were treated with PMe₃ (3 equiv) at 50 °C for 3 h and then with azobenzene at room temperature for 12 h to give 4,5,6-trisubstituted indene derivatives with the loss of one substituent in good yields. This reaction contrasts sharply with our previously reported reaction for the formation of 4,5,6,7-tetrasubstituted indene derivatives without the loss of substituents by the treatment of titanacyclopentadienes with azobenzene without PMe₃. ¹³C NMR spectroscopy of the product derived from a ¹³C-enriched complex revealed that the five carbon atoms originating from a Cp ligand were arranged linearly in the trisubstituted indene derivatives, in contrast to the 4,5,6,7-tetrasubsituted indene derivatives, in which the corresponding five carbon atoms are arranged in a ring.

Metallacyclopentadiene, which is recognized as a metallo-heterocycle, is an important intermediate for the formation of aromatic derivatives. In this short review, we summarized the recent advance on construction of axial, central, planar, and helical chirality by transition-metal-catalyzed aromatic compounds formation via metallacyclopentadienes. J. Heterocyclic Chem., (2011).

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 H₅IO₆ 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.

The synthesis of a series of substituted naphthacene derivatives through the coupling reaction of zirconacyclopentadienes with diiodobenzenes is reported. A reaction of bis(propargyl)benzenes with zirconacene dibutyl afforded the corresponding tricyclic zirconacyclopentadienes, which reacted with o-diiodobenzenes to afford the corresponding dihydronaphthacenes. The yields of the coupling reactions were dependent on the substituents on both of the zirconacycles and o-diiodobenzenes. The reactions of diphenyl-substituted zirconacycles gave higher yields than those of the α,α′-dialkyl-substituted derivatives. The iodide functions thus introduced allowed further introduction of substituents by well-established cross-coupling reactions after construction of the naphthacene skeletons.