Synlett

Lipopolysaccharides (LPSs) are major virulence determinants in Gram-negative bacteria and are responsible for many pathophysiological processes during bacterial infections. However, the accessibility of LPS-associated oligosaccharides for infectious mechanism study and vaccine development remains challenging. We report an efficient stereocontrolled approach for the synthesis of a common inner-core trisaccharide containing difficult-to-access, rare, higher-carbon sugars: a heptose (Hep) and 3-deoxy-α-d-manno-oct-2-ulosonic acid (Kdo). Key features include comprehensive elaboration of a practical synthesis of versatile Hep and Kdo building blocks, and stereoselective assembly of an inner-core trisaccharide from multiple pathogenic bacteria.

(Trifluoromethyl)sulfanylamides are an important class of organic compounds that are common among natural products and drug molecules. Here, we report a (trifluoromethyl)sulfanylation reaction using silver(I) (trifluoromethyl)sulfide as a free-radical (trifluoromethyl)sulfanylation reagent for β-amide compounds. This reaction does not require stoichiometric oxidants or additional transition-metal catalysts, and can be achieved by adding common organic acids. This method has excellent applicability and can accommodate several functional groups, including ester groups, acyl groups, and even bromo or iodo groups. Heterocyclic α,β-amides can also be readily converted into the corresponding products. This reaction also provides a new method for the synthesis of deuterated (trifluoromethyl)sulfanylamides.

Herein, we report the novel strategy for the synthesis of 4-enamino-5-phenyl-2,3-dihydroisothiazole 1-oxides (in other words α-phenyl β-enamino γ-sultims) based on the CSIC reaction. Particularly, readily available α-amino nitriles (the Strecker products) reacted with benzyl sulfinyl chloride to give the corresponding sulfinamides, which upon treatment with excess of LiHMDS converted into the target α-phenyl β-enamino γ-sultims. The method works well and tolerates strained 3- and 4-membered spirocyclic substituents. A preliminary in silico study indicated that the γ-sultim scaffold can be considered a promising pharmacophore template.

Two novel copper-catalyzed cyclization reactions involving a remote propargylic substitution/cyclization/isomerization cascade are disclosed. Derivatives of the seldomly studied heterocycles thieno[2,3-c]pyrrole and thieno[2,3-d]pyridazine are conveniently synthesized in moderate to good yields from primary amines or arylhydrazines through [4+1] and [4+2] reactions, respectively. Preliminary mechanistic experiments corroborated the occurrence of the designed cascade reactions.

A visible-light-catalyzed arylcarboxylation of allenes with CO2 was developed using [Ir(ppy)2(dtbbpy)]PF6 (ppy = 2-phenylpyridine; dtbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) as a photocatalyst to synthesis β-aryl β,γ-unsaturated carboxylic acids. This multicomponent protocol proceeds in an atom-economical way with exclusive regioselectivity. Preliminary mechanistic experiments suggested that allylic carbanion species are the key intermediates.

Synlett 2024; 35: 832-832DOI: 10.1055/s-0043-1763761Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents  |  Full text

Synlett 2024; 35: V-DOI: 10.1055/s-0043-1763762Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

Herein, we present a rapid and efficient method for synthesizing cyclic acetals and ketals utilizing a rotary evaporator. Unlike the conventional Dean–Stark dehydration process, which typically demands extended reaction times and copious amounts of organic solvents, our approach affords the synthesis of cyclic acetals and ketals with varying ring sizes in 30 min while using minimal quantities of dimethyl sulfoxide as the solvent. This innovative protocol features high yields, fast reactions, easy operation, and broad substrate applicability.

An expedient and easy-to-handle synthetic platform has been established for the constructing of 2H-thiophenes carrying fluorine atoms through [4+1] cyclization of enaminothiones with fluorinated carbene precursors. This simple reaction system is well compatible with a wide range of substrates under completely metal-free conditions. The resulting 2H-thiophenes can undergo further late-stage modifications to yield a wide range of fluorine-substituted heterocycles.

Catalytic C–H activation reactions are now established as a means to directly transform organic molecules and are commonly associated with metals such as palladium, rhodium, ruthenium and iridium. This Account will describe a short number of reports demonstrating that structures containing main group elements can facilitate C–H activation processes. In particular, boron-based catalysts can promote catalytic arene C–H borylation reactions, and an emerging approach using phosphenium ions can also cleave sp2 C–H bonds. These processes use a Lewis acidic main group atom combined with a pendant base to cleave C–H bonds, which compares with metal-catalyzed reactions that proceed via concerted metalation deprotonation mechanisms.1 Introduction2 Metal-Catalyzed C–H Activation via CMD/AMLA Mechanisms3 C–H Borylation via Boron-Based Catalysts4 C–H Activation Using Phosphenium Ions5 Conclusions