Chlorinative Cyclization of 1,6-Enynes by Enantioselective Palladium(II)/Palladium(IV) Catalysis

Regio- and Stereoselective Hydrochlorination/Cyclization of 1,n-Enynes by FeCl3 Catalysis

A highly regio- and stereoselective hydrochlorination/cyclization of enynes has been reported by FeCl₃ catalysis. A variety of enynes undergo this cyclization transformation with acetic chloride as the chlorine source and H₂O providing protons via a cationic pathway. This protocol provides a cheap, simple, stereospecific, and effective cyclization to afford heterocyclic alkenyl chloride compounds as Z isomers with high yields (≤98%) and regioselectivity.

Oxidation of Pd(II) with disilane in a palladium-catalyzed disilylation of aryl halides: a theoretical view

Density functional theory (DFT) calculation has been used to reveal the mechanism of the Pd-catalyzed disilylation reaction of aryl halides. The DFT calculations indicate that the reaction starts with the oxidative addition of the C-I bond to the Pd(0) catalyst. Concerted metalation-deprotonation (CMD) can then generate a five-membered palladacycle. Insertion of Pd(ii) into the Si-Si bond in disilane followed by two sequential steps of reductive eliminations yields the disilylation product and regenerates the Pd(0) catalyst. According to the NPA charge analysis along the reaction coordinates, the formal oxidative addition of the Si-Si bond to palladium could be considered as the insertion of palladium into the Si-Si bond. However, the conventional oxidative addition of the C-I bond to palladium is exactly an oxidation process with the electron transfer from the palladium atom to the C-I bond. Therefore, electron rich Pd(0) is beneficial for the oxidation process, and Pd(ii) prone to acquire electrons is beneficial for the insertion process.

PhI(OAc)2-Mediated Dihalogenative Cyclization of 1,6-Enyne with Lithium Halide

The dihalogenative cyclization of 1,6-enyne with the assistance of PhI(OAc)₂ and lithium halide is presented. A plausible radical mechanism is proposed, which consists of addition of halogen radical to alkene, 5-exo-dig radical cyclization of enyne and halogenation via radical coupling. The alkenyl- and alkyl-halide groups in the resulted pyrrolidine products have been demonstrated to be facile handles for further transformations.

Synthesis of Highly Conjugated Functionalized 2-Pyridones by Palladium-Catalyzed Aerobic Oxidative Dicarbonation Reactions of N-(Furan-2-ylmethyl) Alkyne Amides and Alkenes as Coupling Partners

A mild, step-economical method for the synthesis of highly conjugated functionalized 2-pyridones from N-(furan-2-ylmethyl) alkyne amides is reported. This method involves Pd-catalyzed aerobic oxidative dicarbonation reactions of alkynes with carbon nucleophiles of a furan ring and an acrylate or styrene as coupling partners. The UV-vis absorption spectra of some of the 2-pyridones indicated that they absorbed shortwave radiation, suggesting their potential utility for filtration of such radiation.

Palladium-Catalyzed Regioselective Syn-Chloropalladation-Olefin Insertion-Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.

Palladium-catalyzed highly diastereoselective cascade dihalogenation of alkyne-tethered cyclohexadienones via Umpolung of palladium enolate

A highly regio- and diastereoselective Pd(ii)-catalyzed cascade dihalogenation of alkyne-tethered cyclohexadienones proceeding via an electrophilic oxa-π-allyl palladium-species was demonstrated.

Palladacycle catalysis: an innovation to the Suzuki–Miyaura cross-coupling reaction

A new approach to the Suzuki cross-coupling reaction based on the catalysis of a thiosemicarbazone palladacycle is presented.

Structural Features and Asymmetric Environment of i-Pr-SPRIX Ligand

Novel chiral diisopropyl spiro bis(isoxazoline) ligands, anti-i-Pr-SPRIX and syn-i-Pr-SPRIX, were designed and synthesized. Their catalytic utility, X-ray crystallographic analyses, and complexation studies demonstrated the structural features of tetraisopropyl spiro bis(isoxazoline) ligand, i-Pr-SPRIX, which is a prominent ligand in various enantioselective Pd catalytic processes: All i-Pr groups work in collaboration to create an effective asymmetric environment.

Pd-catalyzed enantioselective intramolecular α-arylation of α-substituted cyclic ketones: facile synthesis of functionalized chiral spirobicycles

Synthesis of chiral spirocyclic ketones was accomplishedviathe Pd-catalyzed intramolecular α-arylation of α-substituted cyclic ketones. The obtained spirocyclic ketone could be converted into an acid–base organocatalyst.

Palladium(ii)-catalyzed intramolecular carboxypalladation–olefin insertion cascade: direct access to indeno[1,2-b]furan-2-ones

An efficient intramolecular carboxypalladation–olefin insertion cascade was developed for the synthesis of indeno[1,2-b]furan-2-ones.

Pd(II)-SDP-catalyzed enantioselective 5-exo-dig cyclization of γ-alkynoic acids: application to the synthesis of functionalized dihydofuran-2(3H)-ones containing a chiral quaternary carbon center

The Pd(II)-SDP-catalyzed first enantioselective intramolecular cyclization of α,α-disubstituted γ-alkynoic acids is described. This 5-exo-dig cyclization afforded dihydrofuran-2(3H)-ones bearing a chiral quaternary carbon center in excellent yields with enantioselectivities up to 71%. A mechanism involving palladium(II) species is proposed to rationalize the outcome of the reaction.

Highly stereoselective synthesis of (Z)- and (E)-chloro-substituted-α-methylene-γ-butyrolactone by possibly controlling cis- and trans-chloropalladation

A palladium-catalyzed selective synthesis of cis- or trans-chloro-substituted-α-methylene-γ-butyrolactones from single substrate (propiolic acid) has been realized by controlling cis- or trans-chloropalladation. This method is highly effective for building C-Cl, C-O, and C-C bonds into a one-pot procedure because of its good atom and step efficiency.

Enantioselective cyclization of 4-alkenoic acids via an oxidative allylic C-H esterification

An enantioselective intramolecular oxidative cyclization of 4-alkenoic acids was developed. The reaction proceeded via a π-allyl Pd intermediate generated by an allylic C-H activation to give γ-lactone derivatives with moderate to good enantioselectivity. Spiro bis(isoxazoline) ligand, SPRIX, was indispensable for this asymmetric transformation.