Enantioselective synthesis of axially chiral hydroxy carboxylic acid derivatives by rhodium-catalyzed [2 + 2 + 2] cycloaddition

Axially chiral hydroxy carboxylic acid derivatives were successfully synthesized with high yields and ee values by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed enantioselective [2 + 2 + 2] cycloaddition. Axially chiral hydroxy and dihydroxy carboxylic acid derivatives, bearing the aryl group at the ortho-position of the alkoxycarbonyl group, were also synthesized with high regio- and enantioselectivity.     

Asymmetric synthesis of axially chiral biaryl diphosphine ligands by rhodium-catalyzed enantioselective intramolecular double [2 + 2 + 2] cycloaddition

The concise synthesis of axially chiral biaryl diphosphine ligands by the rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition of hexayne diphosphine oxides has been achieved. These new chiral diphosphine ligands could be employed as a ligand for the rhodium-catalyzed asymmetric catalyses.     

Rhodium-catalyzed [2+2+2] cycloaddition of 1,6-diynes with isothiocyanates and carbon disulfide

[STRUCTURE: SEE TEXT] A neutral rhodium(I)/BINAP complex effectively catalyzed a [2+2+2] cycloaddition of 1,6-diynes with isothiocyanates to give bicyclic thiopyranimines in 59-98% isolated yield. The reaction with carbon disulfide also proceeded to give bicyclic dithiopyrones in 74-85% isolated yield.     

Ruthenium(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes with tricarbonyl compounds

In the presence of catalytic amounts of Cp*Ru(cod)Cl, unsymmetrical 1,6-diynes possessing a variety of functional groups reacted with electron-deficient tricarbonyl compounds at the ketone C=O double bonds to selectively afford dienones via electrocyclic ring opening of the expected alpha-pyrans. The intramolecular Michael addition of the cycloadducts having an acetyl and an alkylidenemalonate moiety gave bicyclo[3.3.0]octenone derivatives.     

Enantioselective synthesis of axially chiral biaryls through rhodium-catalyzed complete intermolecular cross-cyclotrimerization of internal alkynes

[reaction: see text] We have developed a cationic rhodium(I)/H8-BINAP complex-catalyzed complete intermolecular cross-cyclotrimerization of internal alkynes with dialkyl acetylenedicarboxylates. This reaction was successfully applied to enantioselective synthesis of axially chiral biaryls utilizing internal alkynes bearing ortho-substituted phenyl and acetoxymethyl in each terminal position. The axial chirality is constructed at the formation of benzene rings with high enantioselectivity (up to 96% ee).     

Triptycenediols by rhodium-catalyzed [2+2+2] cycloaddition

An efficient, modular synthesis of triptycene derivatives is presented, in which the triptycene ring system is constructed from readily available anthraquinone and alkyne starting materials. A rhodium-catalyzed alkyne cyclotrimerization reaction serves as the key step in this new method for the preparation of these useful unnatural products.     

Enantioselective intramolecular [2+2+2] cycloaddition of triynes for the synthesis of atropisomeric chiral ortho-diarylbenzene derivatives

An iridium-chiral diphosphine complex was used to catalyze an enantioselective [2+2+2] cycloaddition of oxygen- and nitrogen-bridged triynes with ortho-substituted aryl groups on their termini. ortho-Diarylbenzenes with atropisomeric chiralities were obtained in high yield and enantiomeric excess.     

Enantioselective intramolecular [2 + 2 + 2] cycloaddition of enediynes for the synthesis of chiral cyclohexa-1,3-dienes

The enantioselective intramolecular [2 + 2 + 2] cycloaddition of various enediynes, where two acetylenic moieties are connected by a trans-olefinic moiety, gave chiral tricyclic cyclohexa-1,3-dienes using Rh-H8-BINAP catalyst. In the case of carbon-atom-tethered enediynes, enantioselectivity was generally good-to-high regardless of the substituents on their alkyne termini. In contrast, with heteroatom-tethered enediynes, appropriate substituents were required to induce the oxidative coupling of alkyne and alkene moieties before that of two alkyne moieties, which would be important for highly enantioselective intramolecular cycloaddition.     

Enantioselective synthesis of indolizidines bearing quaternary substituted stereocenters via rhodium-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and terminal alkynes

An enantioselective synthesis of indolizidines bearing quaternary substituted stereocenters by way of a rhodium-catalyzed [2+2+2] cycloaddition of substituted alkenyl isocyanates and terminal alkynes is described. The reaction provides lactam products using aliphatic alkynes, whereas aryl alkynes give rise to vinylogous amide products. Through modification of the phosphoramidite ligand, high levels of enantioselectivity, regioselectivity, and product selectivity are obtained for both products.     

Iridium complex-catalyzed highly enantio- and diastereoselective [2+2+2] cycloaddition for the synthesis of axially chiral teraryl compounds

An asymmetric [2+2+2] cycloaddition of an alpha,omega-diyne, possessing ortho-substituted aryl groups on its terminus, and a monoalkyne with oxygen functionalities gave various axially chiral teraryl compounds. The coupling proceeded with extremely high enantio- (>99.5% ee) and diastereoselectivities (dl/meso = >95/5) when catalyzed by an iridium-chiral phosphine complex. As the products were readily transformed into diol compounds by deprotection without racemization, the present procedure provides access to a new chiral pool of diol compounds with C2 symmetry.     

Regioselective [2 + 2 + 2] cycloaddition of a nickel-benzyne complex with 1,3-diynes

[reaction: see text] Reactions of nickel(0)-benzyne complexes with a range of symmetrically substituted 1,3-diynes in the presence of triethylphosphine lead to the regioselective formation of 2,3-dialkynyl naphthalenes. The regioselectivity can be reversed when the diyne possesses substituents of high steric bulk, allowing selective formation of either symmetric dialkynyl naphthalene.     

Density functional theory study of ruthenium (II)-catalyzed [2+2+2] cycloaddition of 1,6-diynes with tricarbonyl compounds

Density functional theory has been employed to study the mechanism of the [2+2+2] ruthenium(II)-catalyzed cycloaddition between 1,6-diynes and tricarbonyl compounds, proposing a viable multistep-pathway according with that was previously suggested, but clarifying some aspects. This process is compared with the one-step reaction in absence of catalyst.     

Enantioselective rhodium-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and terminal alkynes: application to the total synthesis of (+)-lasubine II

The use of TADDOL-based phosphoramidite ligands on rhodium allows for the incorporation of terminal alkynes in the [2+2+2] cycloaddition with alkenyl isocyanates. Terminal aliphatic alkynes provide bicyclic lactams, while the use of aryl alkynes provides complementary access to vinylogous amides. Product selectivity seems to be governed by a combination of electronics and sterics, with smaller and/or more electron-deficient substituents favoring lactam formation. The use of homologous alkenyl isocyanates leads to an expedient asymmetric total synthesis of the alkaloid lasubine II.