Palladium-Catalyzed Asymmetric Reductive Heck Reaction of Aryl Halides

Base-Controlled Palladium-Catalyzed Intramolecular 'One Substrate - Five Reactions' of 5-Benzyl-1-(2-halobenzyl)-2-phenyl-1H-pyrazol-3(2H)-ones

Achieving site-selectivity and chemoselectivity is enormously challenging for substrates with multi-reactive sites in organic reactions. One kind of model substrates, 5-benzyl-1-(2-halobenzyl)-2-phenyl-1H-pyrazol-3(2H)-ones with six reactive sites were chosen as the examples to probe their intramolecular four kinds of five reactions including C(sp³ )-H arylation, C(sp² )-H arylation, reductive Heck reaction, and domino Heck reaction/alkylation of aryl C(sp² )-H bonds through variation of the reaction conditions. Screening of the reaction conditions showed that the different bases controlled the palladium-catalyzed intramolecular site-selectivity and chemoselectivity of the substrates: (i) Cesium carbonate (Cs₂ CO₃ ) promoted the benzyl C(sp³ )-H arylation of the substrates providing dihydropyrazolo[1,5-b]isoquinolin-2(1H)-ones at 100 °C, and isomerization of the dihydropyrazolo[1,5-b]isoquinolin-2(1H)-ones gave isoquinoline derivatives at a higher temperature (140 °C); (ii) Sodium acetate (NaOAc) mediated the aryl C(sp² )-H arylation of the substrates affording seven-membered biphenyl N-heterocycles; (iii) Sodium dichloroacetate (Cl₂ HCCO₂ Na) facilitated occurrence of the reductive Heck reaction of the substrates affording 1H-pyrazolo[5,1-a]isoindol-2(8H)-ones; (iv) Sodium trifluoroacetate (F₃ CCO₂ Na) assisted performance of the domino Heck reaction/aryl C(sp² )-H alkylation of the substrates leading to the spiro heterocycles. The 'one substrate - multiple reactions - multiple products' strategy greatly reduces cost, increases diversity of products, provides more opportunity for screening of pharmaceutical molecules, and enriches modern organic synthetic chemistry.

Pd0 -Catalyzed Asymmetric Carbonitratation Reaction Featuring an H-Bonding-Driven Alkyl-PdII -ONO2 Reductive Elimination

Reductive elimination of alkyl-Pd^II -O is a synthetically useful yet underdeveloped elementary reaction. Here we report that the combination of an H-bonding donor [PyH][BF₄ ] and AgNO₃ additive under toluene/H₂ O biphasic system can enable such elementary step to form alkyl nitrate. This results in the Pd⁰ -catalyzed asymmetric carbonitratations of (Z)-1-iodo-1,6-dienes with (R)-BINAP as the chiral ligand, affording alkyl nitrates up to 96 % ee. Mechanistic studies disclose that the reaction consists of oxidative addition of Pd⁰ catalyst to vinyl iodide, anion ligand exchange between I^- and NO₃ ^- , alkene insertion and S_N 2-type alkyl-Pd^II -ONO₂ reductive elimination. Evidences suggest that H-bonding interaction of PyH⋅⋅⋅ONO₂ can facilitate dissociation of O₂ NO^- ligand from the alkyl-Pd^II -ONO₂ species, thus enabling the challenging alkyl-Pd^II -ONO₂ reductive elimination to be feasible.

Sequential Pd0 - and PdII -Catalyzed Cyclizations: Enantioselective Heck and Nucleopalladation Reactions

An enantioselective consecutive cyclization/coupling process, catalyzed by palladium is reported. Stereoinduction arises from an enantioselective carbopalladation, generating an intermediate which promotes a nucleopalladation step. The dual cyclization sequence was compatible with a variety of alkyne-tethered oxygen- and nitrogen-centered nucleophiles, and a variety of alkenyl-tethered aryl iodides, to forge numerous bisheterocycles in good yields and high regio- and enantioselectivities.

Asymmetric Three-Component Heck Arylation/Amination of Nonconjugated Cyclodienes

Substituted cyclohexylamines are becoming increasingly important in drug discovery. Asymmetric Heck insertion/amination of nonconjugated cyclodienes proceeds to give 5-aryl cyclohexenylamines with good enantioselectivity and exclusive trans configurations. Primary and secondary anilines, indoline, and benzylamines are suitable amines. The weakly donating diphosphite Kelliphite forms a deep unsymmetrical pocket, which is essential for stereoselective anti attack of amines.

Palladium-Catalyzed Asymmetric Intramolecular Reductive Heck Desymmetrization of Cyclopentenes: Access to Chiral Bicyclo[3.2.1]octanes

A palladium-catalyzed asymmetric reductive Heck reaction of unactivated aliphatic alkenes, with eliminable β-hydrogen atoms, has been realized for the first time. A series of optically active bicyclo[3.2.1]octanes bearing chiral quaternary and tertiary carbon stereocenters were obtained in good yields with excellent enantioselectivities, exhibiting good functional-group tolerance and scalability. Moreover, deuterated optically active bicyclo[3.2.1]octanes were also obtained in high efficiency.

Palladium functionalized phosphinite polyethyleneimine grafted magnetic silica nanoparticles as an efficient catalyst for the synthesis of isoquinolino[1,2-b]quinazolin-8-ones

Novel 5-methyl-8H-isoquinolino[1,2-b]quinazolin-8-one derivatives are synthesized using a reusable immobilized palladium catalyzed intramolecular carbon–carbon bond formation.

Regioselective access of alkylidendibenzo[c,f]oxocine framework via cyclocarbopalladation/cross-coupling cascade reactions and reductive Heck strategy

Palladium-catalyzed dual strategies of cascade cyclocarbopalladation/cross-coupling of alkynes and a reductive Heck reaction have been developed to construct dibenzo[c,f]oxocine frameworks with tri- and tetra-substituted exo-cyclic alkenes with high stereo- and regio-control.