Nickel-Catalyzed Carboalkenylation of 1,3-Dienes with Aldehydes and Alkenylzirconium Reagents: Access to Skipped Dienes

Rhodium-catalyzed isomerization of homoallylic alcohols with a tethered carbonyl group: pathway to 1,6-diketones

Herein, we report a rhodium-catalyzed isomerization of homoallylic alcohols with a tethered carbonyl group to synthesize structurally diverse unsymmetrical 1,6-diketones with atom, step, and redox economy. By introducing chiral ligands, good enantioselective isomerization products can be obtained. The utility of this reaction was also demonstrated with diverse transformations.

Dialkylation of 1,3-Dienes with Aldehydes and Cyclopropanols toward Homoallylic Alcohols by Dual Photoredox and Chromium Catalysis

A visible-light-induced three-component coupling of aldehydes, 1,3-dienes, and cyclopropyl alcohols using dual photoredox and chromium catalysis is herein described. This efficient protocol achieves the dialkylation of 1,3-dienes toward 1,4-disubstituted homoallylic alcohols in moderate to good yields with excellent regioselectivity, featuring mild reaction conditions, good functional group tolerance, and gram-scale synthesis. Mechanistic study suggests that photoinduced sequential ring opening of cyclopropyl alcohol and radical and nucleophilic cascade addition are involved in the catalytic cycle.

New insights into the mechanism of synergetic photoredox/copper(i)-catalyzed carbocyanation of 1,3-dienes: a DFT study

This work presents a DFT-based computational study to understand the mechanism, and regio- and enantioselectivities in the synergetic photoredox/copper(i)-catalyzed carbocyanation of 1,3-dienes with alkyl redox-active esters. The calculated results show an unprecedented copper catalytic mechanism, where the reaction follows a catalytic cycle involving CuI-only catalysis, instead of a Cu(i)/Cu(ii)/Cu(iii)/Cu(i) cycle as proposed in the experimental study. Moreover, it is found that the critical step involves the reaction of the cyanocopper(i) species with an allyl cation rather than the cyanocopper(ii) species reacting with an allyl radical as proposed in the experiment, and that the photocatalyst is regenerated via single electron transfer from the allyl radical to the oxidized photocatalyst. In the newly proposed photoredox/copper(i) catalysis, the reaction consists of four stages: (i) generation of the copper(i) active catalyst, (ii) formation of an allyl radical with oxidative quenching of the photoexcited species, (iii) generation of an allylcopper complex accompanied by the regeneration of the photocatalyst, and (iv) formation of the allyl cyanide product with the regeneration of the copper(i) active catalyst. The cyanation of the allyl cation is calculated to be the regio- and enantioselectivity-determining step. The excellent regio- and stereoselectivities are attributed to the favorable CH-π interaction between the substrate and catalyst as well as the small distortion of the substrate.

Origins of Stereospecificity and Divergent Reactivity of Pd-Catalyzed Cross Coupling with α,α-Disubstituted Alkenyl Hydrazones

This article presents an exploration of stereospecificity and divergent reactivity of Pd-catalyzed α,α-disubstituted alkenyl hydrazones to synthesize 1,4-dienes in the Z configuration and vinylcyclopropane. We calculated the energy profiles of four α,α-disubstituted alkenyl hydrazones. The results show that the energy profiles of the whole catalytic cycle are basically the same before the syn-carbopalladation step. Subsequent syn-β-C elimination yields skipping dienes, or direct β-H elimination yields vinylcyclopropane. Current theoretical calculations reveal that the stereospecificity and the divergent reactivity of reactions result from the competition between syn-β-C elimination and β-H elimination. The C-C bond rotation and subsequent syn-β-C elimination step control the stereospecificity of the reaction by changing the olefin stereostructure from E to Z configuration. The steric factor of α-substituted groups mediates the transformation between syn-β-C elimination and β-H elimination. The results are of great significance for the scientific design of substrates to achieve accurate synthesis of target products.

Nickel-Catalyzed Three-Component Cross-Electrophile Coupling of 1,3-Dienes with Aldehydes and Aryl Bromides

We herein report a Ni-catalyzed three-component cross-electrophile coupling of 1,3-dienes with aldehydes and aryl bromides using manganese metal as the reducing agent. This efficient protocol accomplishes dicarbofunctionalization of 1,3-dienes to synthesize diverse structural 1,4-disubstituted homoallylic alcohols by forming two new C-C bonds in one time. Mechanistic study suggests that an allyl-nickel(I) species is involved in the catalytic cycle.

Silaborative Assembly of Allenamides and Alkynes: Highly Regio- and Stereocontrolled Access to Bi- or Trimetallic Skipped Dienes

A highly stereo- and regiocontrolled multicomponent approach to skipped 1,4-dienes decorated with one boryl and two silyl functionalities is described. This Pd-catalyzed atom-economical union of allenamides, alkynes, and Me₂ PhSiBpin (or Et₃ SiBpin) proceeds without the use of phosphine ligands, instead relying on chelation through the internal amide group of the allenamide sulfonyl. A variety of alkynes, including those derived from complex bioactive molecules, can be efficiently coupled with allenamides and Me₂ PhSiBpin in good yields and with excellent selectivity. The synthetic potential was demonstrated through multiple valuable chemoselective transformations, establishing new disconnections for functionalized dienes. Density functional theory calculations revealed that the reaction first proceeded through borylation of the allenamide, followed by silylation of the alkyne and then reductive elimination, which convergently assemble the skipped 1,4-diene.

Divergent Reactivity of α,α-Disubstituted Alkenyl Hydrazones: Bench Stable Cyclopropylcarbinyl Equivalents

Herein we report the divergent reactivity of 2,2-dialkyl-3-(E)-alkenyl N-tosylhydrazones using Pd-catalyzed cross-coupling conditions, which enable the Z-selective synthesis of 3-aryl-1,4-dienes and gem-dialkyl vinylcyclopropanes. We found that the dialkylbiaryl phosphine ligand SPhos was the optimal ligand for this transformation producing skipped dienes in up to 83% isolated yield. The ratio of skipped diene to vinylcyclopropane is dependent on both the structure of the α,α-disubstituted hydrazones and the aryl halide partner. Using sterically encumbered aryl bromides provided the trans-cyclopropane products selectively in up to 69% yield. The reaction is stereospecific and stereoselective and occurs alongside a competing 1,2-alkenyl group migration pathway.

Visible-Light-Triggered Sulfonylation/Aryl Migration/Desulfonylation and C-S/Se Bond Formation Reaction: 1,2,4-Trifunctionalization of Butenyl Benzothiazole Sulfone with Thiosulfonate/Selenosulfonates

A visible-light-triggered radical cascade sulfonylation/aryl migration/desulfonylation and C-S/Se bond formation reaction of butenyl benzothiazole sulfone with thiosulfonates or selenosulfonates is developed. This study affords the 1,2,4-trifunctionalization of butenyl benzothiazole sulfone derivatives under mild conditions.

Reactivity of Stabilized Vinyldiazo Compounds toward Alkenyl- and Alkynylsilanes under Gold Catalysis: Regio- and Stereoselective Synthesis of Skipped Dienes and Enynes

We report the gold-catalyzed reaction of vinyldiazo compounds and alkenylsilanes to produce skipped dienes, which are common structural motifs in an array of bioactive compounds. This carbon–carbon bond-forming transformation proceeds with complete regio- and stereoselectivity with the silyl group serving as a regio- and stereocontrolling element. Likewise, the use of alkynylsilanes as reaction partners yielded skipped enynes resulting from a C(sp)–C(sp³) coupling. Mechanistic experiments and DFT studies have provided support for a stepwise mechanism.

Boron-catalyzed dehydrative allylation of 1,3-diketones and β-ketone esters with 1,3-diarylallyl alcohols in water

A metal-free catalytic allylation with atom economy and green environment friendly was developed. Allylic alcohols could be directly dehydrated in water by B(C6F5)3, without using any base additives. The reaction can afford the corresponding monoallylated product in moderate to high yield and has been performed on a gram-scale, and a quaternary carbon center can be constructed for the active methine compounds of 1,3-diketones or β-ketone esters in this process. The product can be further converted, such as the synthesis of tetra-substituted pyrazole compounds, or 1,4-dienes and functionalized dihydropyrans.

Regio- and Trans-Selective Ni-Catalyzed Coupling of Butadiene, Carbonyls, and Arylboronic Acids to Homoallylic Alcohols under Base-Free Conditions

We herein report a Ni-catalyzed three-component coupling of 1,3-butadiene, carbonyl compounds, and arylboronic acids as a general synthetic approach to 1,4-disubstituted homoallylic alcohols, an important class of compounds, which have previously not been straightforward to access. The reaction occurs efficiently using a Ni(cod)₂ catalyst without any external base and ligand at ambient temperature and allows a highly regioselective and trans-selective 1,4-dicarbofunctionalization of feedstock butadiene in a single operation. This simple and practical protocol could apply to a comprehensive scope of substrates. The neutral conditions show extraordinary tolerance for even highly base-sensitive functional groups.