Diastereocontrol in asymmetric allyl-allyl cross-coupling: stereocontrolled reaction of prochiral allylboronates with prochiral allyl chlorides

Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism

The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism-nucleophilic attack of enolate oxygen on Palladium followed by C-C bond-forming [3,3']-reductive elimination.

Branched/linear selectivity in palladium-catalyzed allyl-allyl cross-couplings: The role of ligands

While Pd-catalyzed allyl-allyl cross-couplings in the presence of small-bite-angle bidentate ligands reliably furnish the branched regioisomer with high levels of selectivity, cross-couplings in the presence of large-bite-angle bidentate ligands give varying, often unpredictable, levels of selectivity. In a combined computational and experimental study, we probe the underlying features that govern the regioselectivity in these metal-catalyzed cross-couplings.

Iridium-catalyzed allyl–allyl cross-coupling of allylic carbonates with (E)-1,3-diarylpropenes

An efficient Ir-catalyzed allyl–allyl cross-coupling reaction of allylic carbonates with (E)-1,3-diarylpropenes was developed to form linear allylated products, 1,5-dienes, regioselectively in excellent yields and with high turnover numbers (up to 2000 S/Ir).

Synthesis of spiroindanes by palladium-catalyzed oxidative annulation of non- or weakly activated 1,3-dienes involving C–H functionalization

The palladium-catalyzed oxidative annulation of non- or weakly activated 1,3-dienes with 2-aryl cyclic 1,3-dicarbonyl compounds is described.

Enantioselective carbocycle formation through intramolecular Pd-catalyzed allyl-aryl cross-coupling

Aryl electrophiles containing tethered allylboronate units undergo efficient intramolecular coupling in the presence of a chiral palladium catalyst to give enantioenriched carbocyclic products. The reaction is found to be quite general, affording 5, 6, and 7-membered carbocyclic products as single regioisomers and with moderate enantioselectivities. Examination of differential coupling partners points to rapid allyl-equilibration as a key stereodefining feature.

Asymmetric palladium-catalyzed allylic alkylation using dialkylzinc reagents: a remarkable ligand effect

A serendipitously discovered palladium-catalyzed asymmetric allylic alkylation reaction with diorganozinc reagents, which displays broad functional group compatibility, is reported. This novel transformation hinges on a remarkable ligand effect which overrides the standard "umpolung" reactivity of allyl-palladium intermediates in the presence of dialkylzincs. Owing to its mild conditions, enantioselective allylic alkylations of racemic allylic electrophiles are possible in the presence of sensitive functional groups.

Congested C-C bonds by Pd-catalyzed enantioselective allyl-allyl cross-coupling, a mechanism-guided solution

Under the influence of a chiral bidentate diphosphine ligand, the Pd-catalyzed asymmetric cross-coupling of allylboron reagents and allylic electrophiles establishes 1,5-dienes with adjacent stereocenters in high regio- and stereoselectivity. A mechanistic study of the coupling utilizing reaction calorimetry and density functional theory analysis suggests that the reaction operates through an inner-sphere 3,3'-reductive elimination pathway, which is both rate-defining and stereodefining. Coupled with optimized reaction conditions, this mechanistic detail is used to expand the scope of allyl-allyl couplings to allow the generation of 1,5-dienes with tertiary centers adjacent to quaternary centers as well as a unique set of cyclic structures.

Catalytic stereospecific allyl-allyl cross-coupling of internal allyl electrophiles with AllylB(pin)

Application of internal electrophiles in catalytic stereospecific allyl–allyl cross-coupling enable the rapid construction of multisubstituted 1,5-dienes, including those with all carbon quaternary centers. Compounds with minimal steric differentiation can be synthesized with high enantiomeric excess.

Stereocontrol in Palladium-Catalyzed Propargylic Substitutions: Kinetic Resolution to give Enantioenriched 1,5-Enynes and Propargyl Acetates

Kinetic resolution during the catalytic allyl-propargyl cross-coupling with chiral starting materials can be accomplished with a chiral Palladium catalyst. These reactions offer ready access to enantiomerically enriched enyne products from simple readily available starting materials.

Catalytic enantioselective allyl-allyl cross-coupling with a borylated allylboronate

Catalytic enantioselective allyl-allyl cross-coupling of a borylated allylboronate reagent gives versatile borylated chiral 1,5-hexadienes. These compounds may be manipulated in a number of useful ways to give functionalized chiral building blocks for asymmetric synthesis.

Copper-catalyzed enantioselective allyl-allyl cross-coupling

A Cu(I)-phosphoramidite-based catalytic system that allows asymmetric allyl-allyl cross-coupling with high enantioselectivity is reported. This transformation tolerates a large variety of functionalized substrates. The versatility of this new reaction is illustrated in the catalytic asymmetric synthesis of the Martinelline alkaloids chromene derivative core.

Copper-catalyzed enantioselective allylic substitution with alkylboranes

The first catalytic enantioselective allylic substitution reaction with alkylboron compounds has been achieved. The reaction between alkyl-9-BBN reagents and primary allylic chlorides proceeded with excellent γ-selectivities and high enantioselectivities under catalysis of a Cu(I)-DTBM-SEGPHOS system. The protocol produces terminal alkenes with an allylic stereogenic center branched with functionalized sp(3)-alkyl groups. The reaction with a γ-silicon-substituted allyl chloride affords an efficient strategy for the enantioselective synthesis of functionalized α-stereogenic chiral allylsilanes.

Construction of 1,5-enynes by stereospecific Pd-catalyzed allyl-propargyl cross-couplings

The palladium-catalyzed cross-coupling of chiral propargyl acetates and allyl boronates delivers chiral 1,5-enynes with excellent levels of chirality transfer and can be applied across a broad range of substrates.

Ni- and Pd-catalyzed synthesis of substituted and functionalized allylic boronates

Two highly efficient and convenient methods for the synthesis of functionalized and substituted allylic boronates are described. In one procedure, readily available allylic acetates are converted to allylic boronates catalyzed by Ni/PCy(3) or Ni/PPh(3) complexes with high levels of stereoselectivity and in good yields. Alternatively, the borylation can be accomplished with commercially available Pd catalysts [e.g., Pd(2)(dba)(3), PdCl(2), Pd/C], starting with easily accessed allylic halides.