Green Synthesis and Catalysis最新文献

A visible-light-induced brominated spirocyclization of N-arylpropiolamides and CBr₄ for the synthesis of 3-bromo-azaspiro[4,5]trienones is reported here. This process allows the formation of C-Br, C-C, and C=O bonds in a single reaction via a cascade radical addition/ipso-cyclization/oxidative dearomatization sequence. This protocol also features high functional group tolerance, operational simplicity and the use of molecular oxygen as an oxidant as well as sustainable photocatalyst- and additive-free reaction conditions at room temperature. Meanwhile, the presented straightforward and sustainable strategy has also been applied to the synthesis of several biologically active compounds.

A selenium-catalyzed electrosynthesis involving regio- and stereo-selective N-olefination of azoles was developed. The room-temperature reaction was efficient (up to 97% yield) and compatible with various styrenes and azoles. Mechanistic study showed that the cascade reaction was triggered by the selenium-cation-mediated electrophilic trans-aminoselenation, and followed by an oxidative cis-elimination of selane. The electrosynthesis was also well compatible with the more challenging internal alkene substrates, giving the desired N-vinyl azoles in up to 88% yield and > 20:1 Z/E ratio.

We report for the first time the combination of directed evolution focused on enhancing and reversing the stereoselectivity of an enzyme with Cu(I)-mediated click chemistry (CuAAC), providing an asymmetric click approach for versatile chiral triazoles products. In this study, the halohydrin dehalogenase HheG was used as the enzyme which was evolved to induce a stereoselective ring-opening reaction of cyclic epoxides in the presence of NaN₃ with the formation of chiral azido products. Two mutants of opposite stereopreference were generated, which convert cyclohexene oxide as well as cycloheptene oxide to (1S, 2S)-2-azidocyclohexanol, (1R, 2R)-2-azidocyclohexanol, (1S, 2S)-2-azidocycloheptanol and (1R, 2R)-2-azidocycloheptanol with essentially high stereoselectivity. The chiral products were then subjected to CuAAC in reactions with structurally different alkynes. Since HheG was found to be compatible with Cu(I), the process was also performed successfully in a unique 2-step one-pot process leading to various chiral triazoles. In order to understand the enhancement and reversal of the evolved enantioselectivity, QM and MD computations were performed. This approach harnesses the modifiability and high stereoselectivity of the evolved biocatalysts in combination with click chemistry. It holds great potential for diverse fields, particularly in the area of pharmaceuticals.

Given the significance of oxacyclic frameworks in molecular scaffolds and drug discovery, it is intriguing to precisely construct and manipulate such ring systems in chemical research. In this area, the intermolecular, multicomponent cyclization for the synthesis of diversely substituted seven-membered ring oxacycles under simple conditions is still a challenge. Here, we report a dual photoredox/Brønsted acid relay catalytic strategy for in situ generation of ortho-quinone methides and subsequent (4+3) cyclization with 2-indolylalcohols. In this one-pot multicomponent reaction, two C-C and one C-O bonds are formed, providing de novo access to various biologically important indole-fused, oxygen-containing seven-membered heterocycles. By virtue of a chiral phosphoric acid, an asymmetric version can also be achieved with good to excellent levels of enantioselectivity (up to 96:4 er).

With reusable sodium decatungstate (NaDT) as the photocatalyst, hydrocarbons (alkanes, ethers and ketones) as the alkylating agents, a wide range of alkylated fused N-heterocycles were obtained in high yield.

Skeletal editing of organophosphines is highly challenging owing to the high P-C bond dissociation energy. Herein, we report an efficient catalyst- and additive-free skeletal editing strategy to transform easily accessible ortho-chalcone based organophosphines into new and complex phosphine oxides, that are unattainable by conventional methods. Water is indispensable to this transformation and serves as the oxygen source to cleave P-C bonds. Interestingly, it is possible to achieve the peripheral modification of organophosphines into phosphonium salts in the absence of water. This water-controlled skeletal editing or peripheral modification strategy is embedded with the merits of high bond- and ring-forming efficiency and complete regio-, chemo- and stereoselectivity.

Vesicles obtained by the self-assembly of asymmetric tetrablock copolymers are a class of materials with fascinating properties. However, simple strategies to synthesize asymmetric tetrablock copolymers are limited. Herein, we have designed and synthesized an initiator which generates radicals by either heating or photoirradiation. Taking the advantages of organocatalyzed reversible complexation mediated radical polymerization which has lower energy requirements, milder reaction conditions, and reduced generation of hazardous byproducts, a three steps synthetic route following "photo-photo-thermal" initiation condition for the preparation of asymmetric CABC tetrablock copolymers with controllable molecular weight, precise block composition and low polydispersity was developed.

Dydrogesterone as an agonist of the progesterone receptor is an important and selective synthetic progesterone used for the treatment of a variety of conditions associated with progesterone deficiency including menstrual cycle regulation, infertility, and prevention of miscarriage. Its manufacturing process employing photochemical reactions remains a significant challenge. Herein we report the first total synthesis of dydrogesterone via a key 10α-substitution-selective dearomative cyclizationfree of photochemical protocols starting from Hajos-Parrish ketone. A gram-scale synthesis is also accomplished from readily available 9-hydroxy-4-androstene-3,17-dione through a novel aromatization-dearomatization strategy of ring A in steroid chemistry. Key synthetic features include a facile chemical aromatization of 9-hydroxy-4-androstene-3,17-dione, efficient ligand-controlled asymmetric dearomative cyclization to install the 10α-Me group, and an effective hydroxyl-directed hydrogenation of sterically congested tetrasubstituted olefin to establish the 8β-H,9β-H stereochemistry.

A Brønsted acid-promoted, metal-free cascade reaction of easily available enamines/imines with diazopyruvates has been demonstrated. With triflic acid as the promoter, the reaction proceeds smoothly at room temperature through sequential diazo protonation, nucleophilic enamine N-addition/C-addition and dehydrative aromatisation in a highly regioselective manner. Interestingly, the regioselectivity of the reaction is governed by the unusual enamine N-nucleophilic addition. The method provides an operationally trivial approach to the synthesis of multisubstituted pyrroles including tri-, tetra-, and penta-substituted derivatives as well as N-H free pyrroles with diverse functionalities in good yields under extraordinarily simple and mild conditions. The utility of the method is illustrated by the rapid assembly of polysubstituted bispyrroles and an array of diversely structured pyrrole derivatives.