From Distillation to Hard Negative Sampling

Proceedings of the 45th International ACM SIGIR Conference on Research and Development in Information Retrieval, Journal Year: 2022, Volume and Issue: unknown

Published: July 6, 2022

Neural retrievers based on dense representations combined with Approximate Nearest Neighbors search have recently received a lot of attention, owing their success to distillation and/or better sampling examples for training -- while still relying the same backbone architecture. In meantime, sparse representation learning fueled by traditional inverted indexing techniques has seen growing interest, inheriting from desirable IR priors such as explicit lexical matching. While some architectural variants been proposed, lesser effort put in models. this work, we build SPLADE expansion-based retriever and show which extent it is able benefit improvements models, studying effect distillation, hard-negative mining well Pre-trained Language Model initialization. We furthermore study link between effectiveness efficiency, in-domain zero-shot settings, leading state-of-the-art results both scenarios sufficiently expressive

Language: Английский

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Novel Stereo‐Induction Pattern in Pudovik Addition/Phospha‐Brook Rearrangement Towards Chiral Trisubstituted Allenes

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: 63(22)

Published: March 23, 2024

Abstract Despite the significance of chiral allene skeletons in catalysis, organic synthesis and medicinal chemistry et al., there is a scarcity reports on axially allenyl phosphorus compounds. Here, we disclosed an efficient straightforward cascade reaction between ethynyl ketones phosphine oxides, resulting broad array trisubstituted allenes incorporating moiety high yields with excellent stereoselectivities facilitated by peptide‐mimic phosphonium salt (PPS) Additionally, comprehensive series mechanistic experiments have been conducted to elucidate that this proceeds via asymmetric Pudovik addition followed subsequent phospha ‐Brook rearrangement occurs concomitantly kinetic resolution, representing stereospecific protonation process facilitating central‐to‐axial chirality transfer manner. We anticipate our research will pave way for promising exploration novel stereo‐induction pattern addition/ reaction.

Language: Английский

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Regiodivergent Organocatalytic Reactions

Catalysts, Journal Year: 2021, Volume and Issue: 11(8), P. 1013 - 1013

Published: Aug. 22, 2021

Organocatalysts are abundantly used for various transformations, particularly to obtain highly enantio- and diastereomeric pure products by controlling the stereochemistry. These applications of organocatalysts have been topic several reviews. emerged as one very essential areas research due their mild reaction conditions, cost-effective nature, non-toxicity, environmentally benign approach that obviates need transition metal catalysts other toxic reagents. Various types including amine catalysts, Brønsted acids, Lewis bases such N-heterocyclic carbene (NHC) cinchona alkaloids, 4-dimethylaminopyridine (DMAP), hydrogen bond-donating gained renewed interest because regioselectivity. In this review, we present recent advances in regiodivergent reactions governed organocatalysts. Additionally, briefly discuss pathways achieving changes conditions solvents, additives, or temperature.

Language: Английский

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Structurally divergent enantioselective synthesis of benzofuran fused azocine derivatives and spiro-cyclopentanone benzofurans enabled by sequential catalysis

Chemical Science, Journal Year: 2023, Volume and Issue: 14(39), P. 10768 - 10776

Published: Jan. 1, 2023

An important objective in organic synthesis and medicinal chemistry is the capacity to access structurally varied complex molecules rapidly affordably from easily available starting materials. Herein, a protocol for divergent of benzofuran fused azocine derivatives spiro-cyclopentanone benzofurans has been developed via chiral bifunctional urea catalyzed reaction between aurone-derived α,β-unsaturated imine ynone followed by switchable annulation reactions Lewis base catalysts (DBU PPh3) with concomitant epimerization. The skeletally diversified products were formed high yields diastereo- enantioselectivities. Computational analysis DFT accurate DLPNO-CCSD(T) employed gain deeper insights into mechanistic intricacies investigate role skeletal diversity.

Language: Английский

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Ruthenium‐Catalyzed C−C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β‐Acetylenic Ketones (Ynones) via Oxidative Alkynylation

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 62(23)

Published: March 31, 2023

Abstract The first metal‐catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β‐acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms transient vinylruthenium complex that deprotonates the terminal active alkynylruthenium nucleophile.

Language: Английский

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Acid-Promoted Phosphorylation of Ynones for the Synthesis of Phosphoryl Enones

Organic Letters, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 23, 2025

An efficient phospha-aldol/Meyer-Schuster rearrangement cascade reaction between propargylic aldehydes and phosphine oxides has been developed in which various phosphoryl enones were obtained moderate to excellent yields. A comprehensive series of mechanistic experiments, including the identification key intermediates application 18O isotope labeling, confirmed that this proceeds through a phospha-aldol followed by Meyer–Schuster reaction.

Language: Английский

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Application of Indolyl Ynones in the Construction of Chiral Carbazoles and Pyrroloindolines by Organo and Metal Sequential Catalysis

Organic Letters, Journal Year: 2025, Volume and Issue: unknown

Published: June 4, 2025

The enantioselective synthesis of carbazoles and pyrroloindolines has been achieved through organo-catalyzed metal sequential-catalyzed one-pot reactions indolyl ynones. Chiral can be synthesized from the ynones nitroolefins an Michael addition followed by a gold-catalyzed Friedel-Crafts reaction/aromatization process. N-tosyl imines lead to generation via Mannich reaction silver-catalyzed dearomatizing spirocyclization/N,N-acetalization cascade reaction.

Language: Английский

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Regio- and enantioselective conjugate addition of β-nitro α,β-unsaturated carbonyls to construct 3-alkenyl disubstituted oxindoles

Chinese Chemical Letters, Journal Year: 2022, Volume and Issue: 34(1), P. 107487 - 107487

Published: May 10, 2022

Language: Английский

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Oxetane-, Azetidine-, and Bicyclopentane-Bearing N-Heterocycles from Ynones: Scaffold Diversification via Ruthenium-Catalyzed Oxidative Alkynylation

Organic Letters, Journal Year: 2023, Volume and Issue: 25(31), P. 5907 - 5910

Published: Aug. 1, 2023

A process for 3-fold scaffold diversification is achieved via ruthenium-catalyzed oxidative alkynylation of commercially available oxetanols, azetidinols and bicyclopentanols to form α,β-acetylenic ketones (ynones), which are subsequently converted oxetane-, azetidine- bicyclopentane-bearing pyrazoles, isoxazoles pyrimidines. one-pot alkynylation-condensation protocol that directly converts azetidine-substituted pyrazoles or pyrimidines demonstrated.

Language: Английский

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Recent advances in [4 + 4] annulation of conjugated heterodienes with 1,4-dipolar species for the synthesis of eight-membered heterocycles

Organic & Biomolecular Chemistry, Journal Year: 2023, Volume and Issue: 22(2), P. 252 - 268

Published: Nov. 28, 2023

Eight-membered heterocycles are important but their synthesis is usually challenging. This review summarizes the recent advances in [4 + 4] annulation of conjugated heterodienes with 1,4-dipolar species for assembling eight-membered heterocycles.

Language: Английский

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