Unsaturated Fatty Alcohol Derivatives as a Source of Substituted Allylzirconocene

Remote Arylative Substitution of Alkenes Possessing an Acetoxy Group via β-Acetoxy Elimination

Palladium-catalyzed remote arylative substitution was achieved for the reaction of arylboronic acids with alkenes possessing a distant acetoxy group to provide arylation products having an alkene moiety at the remote position. The use of β-acetoxy elimination as a key step in the catalytic cycle allowed for regioselective formation of unstabilized alkenes after chain walking. This reaction was applicable to various arylboronic acids as well as alkene substrates.

Stereoselective tandem iridium-catalyzed alkene isomerization-cope rearrangement of ω-diene epoxides: efficient access to acyclic 1,6-dicarbonyl compounds

The Cope rearrangement of 2,3-divinyloxiranes, a rare example of epoxide C-C bond cleavage, results in 4,5-dihydrooxepines which are amenable to hydrolysis, furnishing 1,6-dicarbonyl compounds containing two contiguous stereocenters at the 3- and 4-positions. We employ an Ir-based alkene isomerization catalyst to form the reactive 2,3-divinyloxirane in situ with complete regio- and stereocontrol, which translates into excellent control over the stereochemistry of the resulting oxepines and ultimately to an attractive strategy towards 1,6-dicarbonyl compounds.

Zirconium-Catalyzed Atom-Economical Synthesis of 1,1-Diborylalkanes from Terminal and Internal Alkenes

A general and atom‐economical synthesis of 1,1‐diborylalkanes from alkenes and a borane without the need for an additional H₂ acceptor is reported for the first time. The key to our success is the use of an earth‐abundant zirconium‐based catalyst, which allows a balance of self‐contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H₂ acceptor, which was required in other reported systems. Furthermore, substrates such as simple long‐chain aliphatic alkenes that did not react before also underwent 1,1‐diboration in our system. Significantly, the unprecedented 1,1‐diboration of internal alkenes enabled the preparation of 1,1‐diborylalkanes.

Ru-catalyzed isomerization of ω-alkenylboronates towards stereoselective synthesis of vinylboronates with subsequent in situ functionalization

The stereoselective preparation of synthetically versatile vinylboronates from ω-alkenylboronates is achieved through a ruthenium-catalyzed isomerization reaction. A variety of di- and trisubstituted vinylboronates were conveniently produced and could be used as a new starting point for subsequent in situ remote functionalization through either a sequential Ru/Pd or Ru/Cu double catalytic system.

A regio- and stereoselective ruthenium-catalyzed isomerization of ω-alkenyl boronates into stereodefined di- and trisubstituted alkenylboronate derivatives is reported.

Highly E-Selective, Stereoconvergent Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling of Alkenyl Ethers

An improved method for the nickel-catalyzed Suzuki–Miyaura cross-coupling of alkenyl ethers is reported. This stereoconvergent protocol allows for the utilization of a wide range of alkenyl ethers and aryl boronic esters for the synthesis of variously substituted styrene derivatives. An olefinic mixture with respect to the alkenyl ethers can be employed, thereby circumventing the stereodefined synthesis of starting materials. Preliminary mechanistic investigations indicate a nickel-catalyzed olefin isomerization following initial stereoretentive cross-coupling.

A Tandem Iridium-Catalyzed "Chain-Walking"/Cope Rearrangement Sequence

An iridium-catalyzed tandem olefin migration/Cope rearrangement of alkenyl ω-ene cyclopropanes is reported. By this means, a variety of complex annulenes are obtained as single diastereomers starting from cyclopropyl ester derived from simple 1,ω-dienes and alkenyldiazo compounds. Long-range olefin migration over up to 10 positions could be realized and coupled with an efficient Cope rearrangement to yield valuable scaffolds. Various functional groups are well-tolerated, giving rise to densely functionalized products. Furthermore, the present methodology could be successfully extended to yield bicyclic cycloheptenones starting from readily available alkenyl cyclopropanols via a Kulinkovich reaction.

Remote Nucleophilic Allylation by Allylrhodium Chain Walking

Metal migration through a carbon chain is a versatile method for achieving remote functionalization. However, almost all known examples involve the overall net migration of alkylmetal species. Here, we report that allylrhodium species obtained from hydrorhodation of 1,3-dienes undergo chain walking toward esters, amides, or (hetero)arenes over distances of up to eight methylene units. The final, more highly conjugated allylrhodium species undergo nucleophilic allylation with aldehydes and with an imine to give Z-homoallylic alcohols and amines, respectively.

Zirconocene-Mediated Selective C-C Bond Cleavage of Strained Carbocycles: Scope and Mechanism

Several approaches using organozirconocene species for the remote cleavage of strained three-membered ring carbocycles are described. ω-Ene polysubstituted cyclopropanes, alkylidenecyclopropanes, ω-ene spiro[2.2]pentanes, and ω-ene cyclopropyl methyl ethers were successfully transformed into stereodefined organometallic intermediates, allowing an easy access to highly stereoenriched acyclic scaffolds in good yields and, in most cases, excellent selectivities. DFT calculations and isotopic labeling experiments were performed to delineate the origin of the obtained chemo- and stereoselectivities, demonstrating the importance of microreversibility.

A unique Pd-catalysed Heck arylation as a remote trigger for cyclopropane selective ring-opening

Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C-C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.

Merging allylic C-H bond activation and C-C bond cleavage en route to the formation of a quaternary carbon stereocenter in acyclic systems

This protocol describes a diastereoselective approach for the synthesis of complex molecular architectures containing two stereogenic centers in a 1,4 relationship, one of which being an all-carbon quaternary stereogenic center. Such molecules could be intermediates in the synthesis of steroids, for example. Conceived as a single-flask synthetic sequence from ω-ene cyclopropanes, the protocol involves a concerted allylic C-H and C-C bond activation promoted by the Negishi reagent (Cp₂Zr(η²-butene)). This zirconium-promenade-based procedure affords bifunctionalized products in high diastereomeric ratios after reaction of ω-ene cyclopropanes with the Negishi complex, followed by a thermal treatment and sequential addition of two different electrophiles. The method proves to be particularly efficient when carbonyl compounds are used as first electrophiles and hydrogen or elemental halides are used as second electrophiles. In addition, it offers the opportunity to create new C-C bonds via remote functionalization of a (sp³)-C-H bond, a result of a copper or copper/palladium transmetalation step that extends the scope of the process to alkyl, acyl and aromatic halide compounds as second electrophiles. The typical described protocol allows the synthesis of the highly diastereo-enriched 2-((1R*,2S*)-2-butyl-2 propylcyclopropyl)ethanol and may provide a new entry to access complex molecular segments of natural products such as steroids or C30 botryococcene. It requires a simple reaction setup and takes ∼18.5 h to run the reaction and 2 h for isolation and purification.

Zirconocene-assisted remote cleavage of C-C and C-O bonds: application to acyclic stereodefined metalated hydrocarbons

The molding of molecules through remote functionalisation has increasingly become popular as it provides original and flexible synthetic alternatives to classical retrosynthetic analysis. In this Perspective article, we summarise more than a decade of studies in the specific field of remote activation of inert C-C and C-O bonds using the unique abilities of organozirconocene species mainly from our own research group. By demonstrating that these reactions represent novel and powerful entries towards acyclic stereodefined reactive organometallic species, we aim to show the vast opportunities this concept-driven methodology discovery offers.

Chain Walking of Allylrhodium Species Towards Esters During Rhodium-Catalyzed Nucleophilic Allylations of Imines

Allylrhodium species derived from δ-trifluoroboryl β,γ-unsaturated esters undergo chain walking towards the ester moiety. The resulting allylrhodium species react with imines to give products containing two new stereocenters and a Z-alkene. By using a chiral diene ligand, products can be obtained with high enantioselectivities, where a pronounced matched/mismatched effect with the chirality of the allyltrifluoroborate is evident.

Remote functionalization of hydrocarbons with reversibility enhanced stereocontrol

Remote functionalization of hydrocarbons could be achieved through successive zirconocene-mediated allylic C-H bond activations followed by a selective C-C bond cleavage. Determination of the reaction mechanism by density functional theory (DFT) calculations shows that the high stereocontrol observed in this process results from a large number of energetically accessible equilibria feeding a preferred reactive channel that leads to the major product. A distinctive consequence of this pattern is that stereoselectivity is enhanced upon heating.

An air-stable cationic iridium hydride as a highly active and general catalyst for the isomerization of terminal epoxides

We describe the use of an air-stable iridium hydride catalyst for the isomerization of terminal epoxides into aldehydes with perfect regioselectivity.

Direct Evidence on the Existence of [Mo132] Keplerate-Type Species in Aqueous Solution

We demonstrate the existence of discrete single molecular [Mo(132)] Keplerate-type clusters in aqueous solution. Starting from a discrete spherical [Mo(132)] cluster, the formation of an open-basket-type [Mo(116)] defect structure is shown for the first time in solution using analytical ultracentrifugation sedimentation velocity experiments.

New Multicomponent Approach for the Creation of Chiral Quaternary Centers in the Carbonyl Allylation Reactions

The combined regio- and stereo-controlled carbometalation reaction of alkynyl sulfoxide followed by a zinc homologation and finally an allylation reaction led, in a single-pot operation, to chiral homoallylic alcohols in excellent yields and diastereoselectivities for the creation of chiral quaternary and tertiary centers. The key features in all of the reactions that are described in this article are the high degree of stereocontrol, the level of predictability, and "the ease of execution" which ensures success in the application of such methods. The chiral sulfinyl moiety can be finally removed by simple treatment with alkyllithiums, which allows further functionalizations of the carbon skeleton. By using one of these methods, the creation of chiral quaternary centers with the smallest possible difference, namely CD3 versus CH3 and 13CH3 versus CH3, was easily performed.