Organocatalytic allylic alkylation of alkyne-substituted MBH carbonates: access to quaternary carbon-containing 1,4-enynes.

A DABCO-catalyzed allylic alkylation of tertiary propargylic alcohol-derived MBH carbonates with nitromethane was developed. A series of substituted 1,4-enynes with an all-carbon quaternary stereocenter were efficiently obtained in moderate to high yields. The synthetic utility of the product was demonstrated by facile synthesis of 1,4-enyne-embedded 2-pyrrolidinones.

Catalytic asymmetric synthesis of α-stereogenic carboxylic acids: recent advances.

Chiral carboxylic acids bearing an α-stereogenic center constitute the backbone of many natural products and therapeutic reagents as well as privileged chiral ligands and catalysts. Hence, it is not surprising that a large number of elegant catalytic asymmetric strategies have been developed toward the efficient synthesis of α-chiral carboxylic acids, such as α-hydroxy acids and α-amino acids. In this review, the recent advances in asymmetric synthesis of α-stereogenic free carboxylic acids via organocatalysis and transition metal catalysis are summarized (mainly from 2010 to 2020). The content is organized by the reaction type of the carboxyl source involved, including asymmetric functionalization of substituted carboxylic acids, cyclic anhydrides, α-keto acids, substituted α,ß-unsaturated acids and so on. We hope that this review will motivate further interest in catalytic asymmetric synthesis of chiral α-substituted carboxylic acids.

Direct Noncovalent Activation of α,ß-Unsaturated Aldehydes for the Stereodivergent Synthesis of Substituted Cyclohexenes.

HOMO-raising noncovalent activation of α-aryl α,ß-unsaturated aldehydes using a bifunctional Brønsted base catalyst is achieved. The catalytically generated dienolate intermediate undergoes all-carbon [4+2] cyclizations with nitroolefins, leading to chiral cyclohexenes with four contiguous stereocenters in high yields and with excellent enantioseletivity. Furthermore, the diastereodivergent synthesis of the products is realized by introducing a second steric control to the bifunctional catalyst; 4 isomers out of 16 possible stereoisomers of the products were selectively produced by simple use of two catalysts and their (pseudo)enantiomers. The results presented here provide new insights into the remote activation of the carbonyl functionality as well as the stereodivergent synthesis of complex chiral molecules with multiple stereocenters.

One-pot asymmetric synthesis of quaternary pyrroloindolones through a multicatalytic N-allylation/hydroacylation sequence.

An intramolecular, quaternary carbon center forming hydroacylation of α-substituted acrylates has been discovered. This interesting transformation can be readily incorporated into a multicatalytic tandem process enabled by a combination of nucleophilic tertiary amine and N-heterocyclic carbene catalysis. With no additional stoichiometric base required, this transformation affords the quaternary pyrroloindolones with high levels of enantioselectivity.

Boosting the sonophotocatalytic performance of BiOCl by Eu doping: DFT and an experimental study.

Bismuth oxychloride (BiOCl) has a unique layered structure and uneven charge distribution, resulting in an internal electric field under polarization, which promotes the efficient separation and migration of photogenerated carriers. BiOCl could be a candidate for sonophotocatalysts. However, the low utilization of visible light limits the application of BiOCl in photocatalysts. In this study, the photocatalytic performance of rare earth element (Nd, Sm, Eu, Er and Er)-doped BiOCl was studied by density functional theory (DFT) and experimentally to screen high-performance catalysts. The band structure, density of states, and optical properties were calculated by the DFT method to predict the photocatalytic activity of rare earth-doped BiOCl. The built-in electric field formed in Eu-doped BiOCl inhibiting electron and hole recombination can be observed. Subsequently, the activity of the photocatalyst and sonophotocatalysts was evaluated. The results show that the photocatalytic and sonophotocatalytic activity of Eu-doped BiOCl is improved, which is consistent with the theoretical prediction. Combining theoretical calculations with experiments, the sonophotocatalytic activity of Eu-doped BiOCl is enhanced, mainly due to the synergistic effect of inhibiting carrier recombination, and expansion to the visible light absorption region.

Fe-Catalyzed Sequential C(sp3)-H/N-H Annulation of 2-Methylindoles with Ethyl Trifluoropyruvate at Room Temperature: Construction of Pyrrolo[1,2-α]indoles.

An efficient and benign iron-catalyzed room-temperature method was developed for direct sequential C(sp3)-H/N-H annulation to construct pyrroloindole scaffolds. This strategy features cheap and readily available raw materials and mild room-temperature reaction conditions and provides a green and practical method for the one-pot rapid synthesis of a wide range of diversely functionalized pyrrolo[1,2-α]indoles.

Asymmetric Organocatalytic Synthesis of 2,3-Allenamides from Hydrogen-Bond-Stabilized Enynamides.

Asymmetric catalytic synthesis of 2,3-allenamides from hydrogen-bond-stabilized enynamides in the presence of quinine-based bifunctional squaramide organocatalysts is described. This protocol forms a variety of 2,3-allenamides in high yields and excellent stereoselectivities, in which the elaborated introduction of intramolecular H-bonds within the N, N-bidentate amide group constitutes one of the keys to this highly enantioselective transformation. The synthetic practicality of this reaction has been demonstrated by the axis-to-center chirality transfer of allenamides to furnish enantiomerically enriched building blocks.

Photoredox-Induced Intramolecular 1,5-H Transfer Reaction of Aryl Iodides for the Synthesis of Spirocyclic γ-Lactams.

This work develops a photocatalysis method for the synthesis of γ-spirolactams through a tandem intramolecular 1,5-HAT reaction-cyclization process. A variety of novel γ-spirolactams are prepared in good to excellent yields with this method. This transformation features mild reaction conditions and exceptional functional group tolerance. Additionally, γ-terpinene is applied to this transformation as a hydrogen atom donor for the first time.

A C1-symmetric N-heterocyclic carbene catalysed oxidative spiroannulation of isatin-derived enals: highly enantioselective synthesis of spirooxindole δ-lactones.

A C1-symmetric N-heterocyclic carbene (NHC)-catalysed activation of isatin-derived enals under oxidative conditions was achieved. The in situ generated α,ß-unsaturated acyl azolium species was efficiently trapped by 1,3-dicarbonyl compounds via a Michael addition/spiroannualtion cascade, delivering a series of synthetically important spirooxindole δ-lactones with up to 96% enantioselectivity.

Dearomative Dienolate-Mediated Catalysis: A Remote Activation Strategy for Asymmetric Functionalization of Benzylic C-H Bonds of Heteroaryl Aldehydes.

A dearomative remote activation strategy for the asymmetric functionalization of benzylic C-H bonds of heteroaryl aldehydes under bifunctional Brønsted base catalysis has been developed. The in situ generated o-QDMs-type dienolate intermediates were efficiently and stereoselectively trapped by nitroolefins through an asymmetric Michael/nitro-aldol cascade reaction. Using this strategy, a wide variety of synthetically significant tetrahydrodibenzothiophene and tetrahydrodibenzofuran derivatives were synthesized in good yields with high enantioselectivities.