Organic chemistry frontiers : an international journal of organic chemistry最新文献

The asymmetric Michael addition of phosphorus nucleophiles to electron-deficient alkenes is one of the most direct and atom-economical methods to provide chiral organophosphorus compounds with high efficiency in recent years. Herein, we report a cobalt-catalyzed imidazolyl-directed asymmetric phospha-Michael-type reaction of diarylphosphine oxides with electron-deficient alkenes for synthesizing chiral organophosphorus compounds in moderate to good yields and good to excellent enantioselectivities (25 examples, up to 99% yield, and 99% ee). This protocol features broad substrate scope, good functional group tolerance, and mild conditions as well as avoids the release of massive metal wastes and the use of noble transition metal catalysts. The excellent enantioselectivity of the phospha-Michael reaction can be due to the adoption of a novel chiral N4-ligand. Furthermore, the DFT calculation indicates that the bulky 2,4,6-(i-Pr)₃C₆H₂ group of the ligand induces large steric hindrance which blocks the nucleophilic attack from the Si-face.

From the historical perspective, all widely accepted privileged chiral ligands tune the catalytic activity of the metal complexes that they form and impart stereoselectivity to asymmetric reactions exclusively relying on the coordination with phosphorus, nitrogen or hetero-atom hybrids. Nowadays, works with N,N’-dioxide amides, i.e., Feng ligands, break with this tradition and have shown that oxygen-coordinated ligands can also be privileged, allowing for the proliferation of chiral metal catalysts and highly enantioselective transformations.

A synthetic method that relies on [Au₂(μ-dppm)₂]Cl₂ (dppm = bis(diphenylphosphino)methane) and UVA LED (LED = light emitting diode) light (λ = 365 nm) to mediate the α-alkynylation of tertiary α-silylamines by 1-iodoalkynes is described. The site-selective desilylative C(sp³)–C(sp) bond formation protocol was demonstrated to exhibit excellent functional group tolerance as it was applicable to a broad range of coupling partners and a variety of bioactive molecules and natural products. Experimental and computational studies suggest the reaction mechanism follows an oxidative quench pathway that generates the two surmised radical species of the amine and alkyne substrates. It also implied the possible involvement of the dimeric metal complex in mediating the ensuing cross-coupling of the two radical species, which is unprecedented in photoredox gold(i,i) catalysis.

C–H annulations at N- and C2-aryls of an imidazole have been researched well, while the annulation on C4(5)-aryls especially the reactivity and site-selectivity among these aryls remains unknown. Herein, a molecular engineering strategy involving six reaction modes based on the rhodium-catalyzed C4(5)_aryl–H activation/annulation of imidazoles with alkynes has been developed, giving diverse neutral/cationic N-heterocycles with broad scope (>60 examples) and high selectivity. More importantly, through a series of intramolecular competition experiments and DFT calculations, the reactivity of the peripheral C–H bonds has been studied and ranked for the first time: C2_aryl–H > C4(5)_aryl–H > C4(5)_styryl–H/C2_styryl–H > residual C4(5)_aryl–H/C4(5)_styryl–H. Furthermore, the remote bulky C2-subsituent is found to have a big influence on the regioselectivity of C4(5)_aryl–H activation.

A method for direct oxidation of boronic esters to the carbonyl groups has been established herein. Under the irradiation of visible light and O₂ atmosphere, ketones and aldehydes can be obtained in moderate to excellent yields. Using tetrabutylammonium tribromide (TBATB) as the catalyst, this procedure avoids using of metal-based (photo)catalysts. α-Borylalkyl radicals have been proposed as the key intermediates of this oxidation process.

A new fan-like adaptive porous organic cage (FPOC) was synthesized for the structure determination of liquid perfume molecules. The FPOC was used as a molecule catcher because (i) it contains extrinsic cavities in the network; (ii) the CN moiety can be used as the hydrogen bond acceptor, and the numerous hydrocarbons can be used as hydrogen bond donors; and (iii) the rich benzene rings can form aromatic interactions. The liquid perfume guests 1–9 [N,N-diethyl-3-methylbenzamide (1), 1,3-dimethoxybenzene (2), toluene (3), eugenyl acetate (4), (E)-methyl isoeugenol (5), (R)-carvone (6), (S)-carvone (7), trans-anethole (8) and 1,8-cineole (9)] are successfully encapsulated in the extrinsic cavity of the FPOC and ten new crystals were obtained (including the cage). Theoretical calculations using Multiwfn software showed that the guest volumes were found to be in a wide range from 180.189–661.027 ų, indicating that the FPOC was guest adaptive. To the best of our knowledge, this is the first report on the encapsulation properties between an adaptive porous organic cage and liquid perfume molecules. All guests form C–H⋯π or C–H⋯O interactions with the FPOC, highlighting the important role of weak interactions in the structure determination of liquid perfume molecules.

Kinetic resolution is a practical method that affords recovered starting materials and products in high enantiomeric excess from relatively simple racemic starting materials. However, intramolecular kinetic resolution is less reported due to its high reliance on designed substrates and catalysts that must match perfectly compared to intermolecular pathways. In this review, achievements in intramolecular kinetic resolution have been summarized and systematically discussed. The current review is divided into five sections based on different reaction types, mainly including cyclization, elimination, isomerization, rearrangement and miscellaneous reactions. The aim of this review article is to highlight the importance and elegance of this specialized resolution pathway in the construction of important and attractive chiral skeletons.

A palladium-catalyzed cascade reaction for the synthesis of tetrahydro-β-carbolines and other polycyclic indoles from 2-(hydroxyenyl)sulfonanilides by combining the Pd(ii)-catalyzed cyclization of alkynes and intramolecular redox-relay Heck arylation of alkenols is presented. This method enables the construction of two rings and installs a remote carbonyl group in a single operation, offering broad synthetic utility for further elaborations.

Herein, we report the use of the readily available and bench-stable pyrimidinyl sulfones as electrophiles in Ni-catalyzed Suzuki−Miyaura cross-coupling reactions. This method allows the facile synthesis of 2,4-disubstituted pyrimidines that are pharmaceutically relevant. These reactions were carried out under mild conditions and show a remarkable substrate scope. In this approach, the C–sulfone bond is cleaved efficiently and regioselectively. Preliminary mechanistic studies revealed the importance of the α-nitrogen atom in pyrimidine in facilitating these transformations.

M₄L₂ metalla-cages bearing large electron-rich ovoid cavities constructed through coordination-driven self-assembly from square planar palladium complexes and extended tetrathiafulvalene (exTTF)-based ligands are depicted. Their binding properties for polyaromatic hydrocarbons (PAHs) or zinc tetraphenylporphyrin have been evaluated and compared with previously described smaller cage analogues, showing a high size selectivity.