Synthesis of cyclopentadienones catalyzed by methylidynetricobalt nonacarbonyl

Oxygen-Linked Cyclopentadienyl Rhodium(III) Complexes-Catalyzed Asymmetric C-H Arylation of Benzo[h]quinolines with 1-Diazonaphthoquinones

Chiral cyclopentadienyl rhodium (CpRh) complex-catalyzed asymmetric C-H functionalization reactions have witnessed a significant progress in organic synthesis. In sharp contrast, the reported chiral Cp ligands are limited to C-linked Cp and are often synthetically challenging. To address these issues, we have developed a novel class of tunable chiral cyclopentadienyl ligands bearing oxygen linkers, which were efficient catalysts for C-H arylation of benzo[h]quinolines with 1-diazonaphthoquinones, affording axially chiral heterobiaryls in excellent yields and enantioselectivity (up to 99 % yield, 98.5:1.5 er). Mechanistic studies suggest that the reaction is likely to proceed by electrophilic C-H activation, and followed by coupling of the cyclometalated rhodium(III) complex with 1-diazonaphthoquinones.

Cobalt-catalyzed carbonylative cycloaddition of substituted diynes to access complexed polycyclic compounds

A cobalt-catalyzed domino Pauson–Khand and [4 + 2] cycloaddition of substituted diynes has been developed for the rapid construction of complexed polycyclic ring systems.

Construction of Fused Tropone Systems Through Intramolecular Rh(I)-Catalyzed Carbonylative [2+2+2+1] Cycloadditon of Triynes

“Tropone” is a non-benzenoid aromatic skeleton that can be found in a variety of natural products. This cyclohepta-2,4,6-trien-1-one skeleton appears simple, but there have been no straightforward ways to construct this molecular architecture. It is conceivable that this molecule can be constructed via a higher order cycloaddition of three acetylene units and CO, but such process was not known until we have discovered that the carbonylative [2+2+2+1] cycloaddition of triynes can take place in the presence of a Rh complex catalyst and CO. However, this highly challenging process is naturally accompanied by ordinary [2+2+2] cyclotrimization products, i.e., benzenes, as side products. A mechanistic study led to two competing processes wherein the critical CO insertion occurs either to a rhodacyclopentadiene intermediate (Path A) or a rhodacycloheptatriene intermediate (Path B). The DFT analysis of those two pathways disclosed that the Path A should be the one that yields the carbonylative [2+2+2+1] cycloaddition products, i.e., fused tricyclic tropones. A further substrate design, inspired by colchicine structure, led to the almost exclusive formation of a fused tetracyclic tropone from a triyne bearing 1,2-disubstituted benzene moiety in a single step and excellent yield.

Synthesis of [RhCl(CO)(cyclopentadienone)]2 from [RhCl(cod)]2 and a 1,6-diyne under CO: application to Rh(I)-catalyzed tandem [2+2+1] carbonylative cycloaddition of diynes and Claisen rearrangement

Although Rh(I)Cl(CO)(cpd) (cpd = cyclopentadienone) complexes were identified more than 40 years ago, their exact structures have not been determined because of the polymeric nature of these complexes. We determined the structure of [Rh(I)Cl(CO)(cpd)](2), which was formed by the reaction of [Rh(cod)Cl](2) with a 1,6-diyne under CO. In addition, based on determination of the structure of the [Rh(I)Cl(CO)(cpd)](2) complex, we identified a new catalytic tandem reaction--the Rh-catalyzed [2+2+1] carbonylative cycloaddition of phenoxide-substituted diynes and Claisen rearrangement.

Synthesis, structure, and reactivity of naphthalyne-Co2(CO)6 complexes

Synthesis of naphthalyne-Co2(CO)6 complexes, the first example of the aryne-Co2(CO)6 complex, was achieved via cyclization of acyclic alkyne-Co2(CO)6 complex precursors containing an allylsilane and an aldehyde moiety followed by dehydration. Unique reactivities of the complexes toward oxygen to give carboxylic acid derivatives and toward alkynes to give cyclopentadienone derivatives were also disclosed.

Rhodium-Catalyzed [2+2+1+1] Cyclocarbonylative Coupling of Alkynes with Carbon Monoxide Affording Tetrasubstitutedp-Benzoquinones

In this strategy, the tetrasubstituted benzoquinones have been prepared directly by a [2+2+1+1] cyclocarbonylative coupling reaction of internal alkynes with CO in the presence of [RhCl(CO)2]2. The low concentration of CO in the reaction is the crucial point for the chemoselective formation of tetrasubstituted benzoquinones in good to high yields. Functional groups such as chloro, methoxy, cyano, vinyl, fluoro, and carboxylate are tolerated under the reaction conditions.

Catalytic activity of dodecacarbonyltetracobalt in aqueous media: a “greening” of the Pauson–Khand reaction

The unprecedented reactivity of Co(4)(CO)(12) with enynes under aqueous conditions, representing the development of a mild and simple aqueous-phase cobalt-catalyzed PK reaction protocol, is described herein.

Indolophanetetrayne cobalt complexes via Nicholas reactions

[reaction: see text] Indole N-substituted diyne tetracobalt complexes (4) undergo a Lewis acid mediated dimerization-cyclization reaction through the indole 3-position to afford indolophanetetrayne cobalt complexes (7). Substitution of the indole fragment of (4) with a 3-methyl function allows analogous formation of indolophanetetrayne complex (9), linked through the indole 2-position.

Tethered 2 + 2 + 2 cycloaddition reactions of cobalt–cycloheptyne complexes

Cycloheptyne-dicobalt hexacarbonyl complexes, substituted by propargylic ether functions, undergo 2 + 2 + 2 cycloaddition reactions with alkynes to give tricyclic benzocycloheptanes; an all-intramolecular version of this transformation is also possible.