In Silico Investigation of Palladium-Catalyzed Chemoselective Monoalkoxycarbonylation of 1,3-diynes for Conjugated Enynes Synthesis.

The palladium-catalyzed monoalkoxycarbonylation of 1,3-diynes provides a chemoselective method for the construction of synthetically useful conjugated enynes. Here, in silico unraveling the detailed mechanism of this reaction and the origin of chemoselectivity were conducted. It is shown that the alkoxycarbonylation reaction preferably proceeds by a NH-Pd pathway, which including three substeps: hydropalladation, CO migratory insertion and methanolysis. The effectiveness of the NH-Pd catalytic system is attributed to the alkynyl-palladium π-back-bonding interaction, C-H⋅⋅⋅π interaction in reactant moiety and d-pπ conjugation between the Pd center and alkenyl group. The hydropalladation step was identified as the rate- and chemoselectivity-determining step, and the first alkoxycarbonylation requires a much lower energy barrier in comparison with the second alkoxycarbonylation, in line with the experimental outcomes that the monoalkoxycarbonylation product was obtained in high yield. Distortion-interaction analysis indicates the more favorable monoalkoxycarbonylation (compared to double alkoxycarbonylation) is caused by steric effect.

Synthesis of Ester-Containing Chroman-4-Ones via Cascade Radical Annulation of 2-(Allyloxy)Arylaldehydes with Oxalates under Metal Free Conditions.

A convenient and practical method for the synthesis of bioactive ester-containing chroman-4-ones through the cascade radical cyclization of 2-(allyloxy)arylaldehydes and oxalates is described. The preliminary studies suggest that an alkoxycarbonyl radical might be involved in the current transformation, which was generated via the decarboxylation of oxalates in the presence of (NH4)2S2O8.

27 Years of Catalytic Carbonylative Coupling Reactions in Hungary (1994-2021).

Palladium-catalyzed carbonylation reactions, in the presence of nucleophiles, serve as very potent tools for the conversion of aryl and alkenyl halides or halide equivalents to carboxylic acid derivatives or to other carbonyl compounds. There are a vast number of applications for the synthesis of simple building blocks as well as for the functionalization of biologically important skeletons. This review covers the history of carbonylative coupling reactions in Hungary between the years 1994 and 2021.

Iron-Catalyzed Alkoxycarbonylation of Alkyl Bromides via a Two-Electron Transfer Process.

Transition metal-catalyzed carbonylative cross-coupling reactions are some of the most widely used methods in organic synthesis. However, despite the obvious advantages of iron as an abundant and low toxicity transition metal catalyst, its practical application in carbonylation reaction remains largely unexplored. Here we report our recent study on Fe-catalyzed alkoxycarbonylation of alkyl halides. Mechanistic studies indicate that the reaction is catalyzed by an in situ generated Fe2- complex. This low-valent iron species activates alkyl bromides via a distinctive two-electron transfer (TET) process, whereas it proceeds via a single electron transfer (SET) process for alkyl iodides which is consistent with literature.

Pd-Catalyzed C(sp2 )-H Alkoxycarbonylation of Phenethyl- and Benzylamines with Chloroformates as CO Surrogates.

The site-selective functionalization of C-H bonds within a complex molecule remains a challenging task of capital synthetic importance. Herein, an unprecedented Pd-catalyzed C(sp2 )-H alkoxycarbonylation of phenylalanine derivatives and other amines featuring picolinamide as the directing group (DG) is reported. This oxidative coupling is distinguished by its scalability, operational simplicity, and avoids the use of toxic carbon monoxide as the C1 source. Remarkably, the easy cleavage of the DG enables the efficient assembly of isoindolinone compounds. Density Functional Theory calculations support a PdII /PdIV catalytic cycle.

Palladium-Catalyzed Enantioselective Alkoxycarbonylation of Propargylic Carbonates with (R)- or (S)-3,4,5-(MeO)3 -MeOBIPHEP.

(R)- and (S)-3,4,5-(MeO)3 -MeOBIPHEP have been identified as the efficient chiral ligands for the palladium-catalyzed highly enantioselective synthesis of 2,3-allenoates from different types of easily available racemic propargylic carbonates with 90-98 % ee and decent yields. The potential of the products was demonstrated with high chirality transfer efficiency.

Efficient and Recyclable RuCl3 ⋠3H2O Catalyst Modified with Ionic Diphosphine for the Alkoxycarbonylation of Aryl Halides.

A series of ionic (mono-/di-)phosphines (L2, L4, and L6) with structural similarity and their corresponding neutral counterparts (L1, L3, and L5) were applied to modulate the catalytic performance of RuCl3 ⋅ 3H2O. With the involvement of the ionic diphosphine (L4), in which the two phosphino-fragments were linked by butylene group, RuCl3 ⋅ 3H2O with advantages of low cost, robustness, and good availability was found to be an efficient and recyclable catalyst for the alkoxycarbonylation of aryl halides. The L4-based RuCl3 ⋅ 3H2O system corresponded to the best conversion of PhI (96 %) along with 99 % selectivity to the target product of methyl benzoate as well as the good generality to alkoxycarbonylation of different aryl halides (ArX, X=I and Br) with alcohols MeOH, EtOH, i-PrOH and n-BuOH. The electronic and steric effects of the applied phosphines, which were analyzed by the 31P NMR for 1 J 31 P- 77 Se 1 J measurement and single-crystal X-ray diffraction, were carefully co-related to the performance RuCl3 ⋅ 3H2O catalyst. In addition, the L4-based RuCl3 ⋅ 3H2O system could be recycled successfully for at least eight runs in the ionic liquid [Bmim]PF6.

Gas chromatographic-mass spectrometric characterization of thebaol, an opium constituent, and its structural analogs.

A GC-MS method is described for the characterization of thebaol, a component of opium poppy. The method includes preliminary sample derivatization to TMS, TBDMS, TFA, PFP and HFB substituted products. Fragmentation of resulting derivatives is unique under electron ionization, and proceeds via consecutive loss of two radicals that violate the "even-electron rule". Peaks of [M-2CH3]+. and [M-C4H9-CH3]+. ions show maximum intensities in the spectra of trimethyl- and tert-butyldimethylsilyl-thebaols. Elimination of perfluoroalkyl and methyl radicals from M+. is characteristic for TFA, PFP and HFB thebaols. The same fragmentation peculiarity is characteristic for derivatives prepared from related natural compounds containing vicinal 2-methoxyphenol moieties. The unique fragmentation of trialkylsilyl and perfluoroacyl derivatives of thebaol can be successfully used for thebaol determination within complex mixtures. This is part 4 from the series "Analytical derivatives in mass spectrometry", parts 1, 2 and 3 see [1-3].

Immobilization of Carbonylcobalt Catalyst by Poly(4-vinylpyridine) (P4VP) through N→Co Coordination Bonds: The Promotional Effect of Pyridine and the Reusability of Polymer Catalyst.

A carbonylcobalt catalyst, immobilized by poly(4-vinylpyridine) (P4VP) through N→Co coordination bonds, has been prepared by solvothermal method. It has been revealed that the pyridine fragments in the polymer catalyst act not only as promoters to improve the catalytic performance of the carbonylcobalt catalyst for alkoxycarbonylation of ethylene oxide to methyl 3-hydroxypropanoate but also as stabilizers to enhance the reusability of the polymer catalyst. Furthermore, the polymer catalyst could be easily separated by filtration and reused with only a slight loss of catalytic efficiency.

Multifunctional Single-Site Catalysts for Alkoxycarbonylation of Terminal Alkynes.

A multifunctional copolymer (PyPPh2 -SO3 H@porous organic polymers, POPs) was prepared by combining acidic groups and heterogeneous P,N ligands through the copolymerization of vinyl-functionalized 2-pyridyldiphenylphosphine (2-PyPPh2 ) and p-styrene sulfonic acid under solvothermal conditions. The morphology and chemical structure of the copolymer were evaluated using a series of characterization techniques. Compared with traditional homogeneous Pd(OAc)2 /2-PyPPh2 / p-toluenesulfonic acid catalyst, the copolymer supported palladium catalyst (Pd-PyPPh2 -SO3 H@POPs) exhibited higher activity for alkoxycarbonylation of terminal alkynes under the same conditions. This phenomenon could be attributed to the synergistic effect between the single-site Pd centers, 2-PyPPh2 ligands, and SO3 H groups, the outstanding swelling properties as well as the high enrichment of the reactant concentration by the porous catalyst. In addition, the catalyst could be reused at least 4 times without any apparent loss of activity. The excellent catalytic reactivity and good recycling properties make it an attractive catalyst for industrial applications. This work paves the way for advanced multifunctional porous organic polymers as a new type of platform for heterogeneous catalysis in the future.

Synthesis of new diphosphine ligands and their application in Pd-catalyzed alkoxycarbonylation reactions.

Carbocyclic and N-heterocyclic analogues of the industrially applied ligand bis(di-tert-butylphosphinomethyl)benzene (1) have been synthesized in moderate to very good yields. The new ligands are based on benzene, tetralin, lutidine, pyrazine, quinoxaline, and maleimide backbones. Electronic and steric variations of the phosphorous donor sites were performed. As a benchmark reaction, the palladium-catalyzed methoxycarbonylation of 1-octene has been tested. Ester yields up to 64% and high linear selectivities up to 92% were achieved.