Yuya Hu

Going for a ′SPIN′: The enantioselective synthesis of a series of 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed using a sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF₃‐promoted diastereoselective spirocyclization. Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands.

Abstract

The enantioselective synthesis of a series of C₂‐symmetric 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed by sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF₃‐promoted diastereoselective spirocyclization (>20:1 d.r. and >99 % ee for all examples). Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands.

Synlett
DOI: 10.1055/s-0037-1611381

Amines are an important class of compounds in organic chemistry and serve as an important motif in various industries, including pharmaceuticals, agrochemicals, and biotechnology. Several methods have been developed for the C–H functionalization of amines using various directing groups, but functionalization of free amines remains a challenge. Here, we discuss our recently developed carbon dioxide driven highly site-selective γ-arylation of alkyl- and benzylic amines via a palladium-catalyzed C–H bond-activation process. By using carbon dioxide as an inexpensive, sustainable, and transient directing group, a wide variety of amines were arylated at either γ-sp3 or sp2 carbon–hydrogen bonds with high selectivity based on substrate and conditions. This newly developed strategy provides straightforward access to important scaffolds in organic and medicinal chemistry without the need for any expensive directing groups.1 Introduction2 C(sp3)–H Arylation of Aliphatic Amines3 C(sp2)–H Arylation of Benzylamines4 Mechanistic Questions5 Future Outlook
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© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Waste not, want not: Benzyl alcohols underwent C−C bond formation with alkynes under thermal conditions in the presence of a catalytic amount of KO^tBu to provide α‐alkylated ketones with 100 % atom economy (see scheme). The reaction showed unusual regioselectivity to give products in which the C=O group was located on the side of the molecule derived from the alcohol.

Abstract

We report a C−C bond‐forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO^tBu to form α‐alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.

Matchmaker: The commercially available precatalyst system MesCu/(R,R)‐Ph‐BPE couples Ph₃SiH with the fast‐reacting enantiomer of racemic mixtures of tertiary propargylic alcohols. This non‐enzymatic kinetic resolution provides access to synthetically valuable and versatile enantiomerically enriched tertiary propargylic alcohols and the corresponding silyl ethers (see scheme).

Abstract

A broad range of tertiary propargylic alcohols were kinetically resolved by catalyst‐controlled enantioselective silylation. This non‐enzymatic kinetic resolution is catalyzed by a Cu−H species and makes use of the commercially available precatalyst MesCu/(R,R)‐Ph‐BPE and a simple hydrosilane as the resolving reagent. Both alkyl,aryl‐ as well as dialkyl‐substituted propargylic alcohols participate, and especially high selectivity factors are achieved when the alkyne terminus carries a TIPS group, which also enables facile post‐functionalization in this position (s up to 207).

Just diene to be arylated: A strategy was developed for the chemoselective hydroarylation of 1,3‐dienes with phenols through a borane‐promoted protonation/Friedel–Crafts‐type mechanism (see scheme). The transformation showed good functional‐group compatibility for the efficient synthesis of diverse ortho‐allyl phenols.

Abstract

A B(C₆F₅)₃‐catalyzed hydroarylation of a series of 1,3‐dienes with various phenols has been established through a combination of theoretical and experimental investigations, affording structurally diverse ortho‐allyl phenols. DFT calculations show that the reaction proceeds through a borane‐promoted protonation/Friedel–Crafts pathway involving a π‐complex of a carbocation–anion contact ion pair. This protocol features simple and mild reaction conditions, broad functional‐group tolerance, and low catalyst loading. The obtained ortho‐allyl phenols could be further converted into flavan derivatives using B(C₆F₅)₃ with good cis diastereoselectivity. Furthermore, this transformation was applied in the late‐stage modification of pharmaceutical compounds.

Abstract

Among the attempts to consolidate the so‐called circular economy, the conversion of carbon dioxide (CO₂) into added‐value products has gained more and more attention during the last three decades. One of the feasible applications of CO₂ as a C₁ building block is its incorporation into cyclic organic carbonates (COCs) and aliphatic polycarbonates (APCs) by reaction with epoxides. A plethora of homogeneous catalytic systems has been reported to promote this reaction, based mainly on magnesium, aluminium, cobalt, chromium and zinc complexes. Despite the abundance and low toxicity of iron, only few examples of catalysts based on this metal had been reported until fifteen years ago, and relevant advances were made only during the last decade. This review seeks to cover this progress and to give a renewed impulse for further research into iron utilisation in this kind of catalysis.

Abstract

Various CO₂ adducts of tetra‐hydropyrimidin‐2‐ylidene (THPE) derived from the commercially available 1, 5‐diazabicyclo[4.3.0]non‐5‐ene (DBN) were firstly synthesized. X‐ray single crystal analysis revealed the bent geometry of the binding CO₂ having an O−C−O angle of 127.50∼129.51° for THPE−CO₂ adducts. In situ FTIR experiments demonstrated that THPE−CO₂ adducts had unprecedented thermal stability in DMSO, even at 100 °C without decomposition. It was found that the THPE−CO₂ adducts were highly active in catalyzing the carboxylative cyclization of CO₂ with propargylic alcohols under mild conditions, significantly higher than the previously reported organocatalysts. Various internal and terminal functionalized propargylic alcohols were tolerated in these processes to afford the corresponding α‐alkylidene cyclic carbonates in moderate to good yields with complete (Z)‐stereoselectivity. Isotope labeling, in combination with in‐situ FTIR and stoichiometric experiments, reveal that the catalytic reaction tends to proceed via the THPE−CO₂‐mediated basic ionic pair mechanism.

Manganese can label it: A metal‐catalyzed methylation process has been developed. By employing an air‐ and moisture‐stable manganese catalyst together with isotopically labeled methanol, a series of D‐, CD₃‐, and ¹³C‐labeled products were obtained in good yields under mild reaction conditions with water as the only byproduct.

Abstract

A metal‐catalyzed methylation process has been developed. By employing an air‐ and moisture‐stable manganese catalyst together with isotopically labeled methanol, a series of D‐, CD₃‐, and ¹³C‐labeled products were obtained in good yields under mild reaction conditions with water as the only byproduct.

OMEGA is not the end: A nanocrystalline ruthenium catalyst, embedded into a zeolite, catalyses the hydrogenolysis of cyclic carbonates into glycols and methane. The catalyst displays unprecedented selectivity towards methane, and the reaction may be considered as an extension of the OMEGA process, in which both a valuable liquid and gaseous product are formed.

Abstract

We report a ruthenium‐modified zeolite which efficiently transforms propylene carbonate to propylene glycol and methane, under solvent‐free conditions. The catalyst achieved high product selectivity and no significant ageing effect was observed after multiple cycles. The resulting liquid product (water‐containing glycol) can be directly used as anti‐freeze solution and the gas phase can directly be used as an energy carrier in the form of H₂‐enriched methane. This process efficiently bridges energy storage and an important chemical synthesis under sustainable (CO₂ consuming) conditions.

Genome-edited baby claim provokes international outcry

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