Beilstein Journal of Organic Chemistry最新文献

The use of 1,3-diamino-2-propanol with competitive N- and O-nucleophilic centers in a three-component cyclization with ethyl 4,4,4-trifluoroacetoacetate and methyl ketones enables the synthesis to be carried out for octahydropyrido[1,2-a]pyrimidin-6-ones and hexahydrooxazolo[3,2-a]pyridin-5-ones, the preferential formation of which depends on the substituent in the methyl ketone component. Dual acid-base catalysis of the reactions with alkyl methyl ketones increases the regioselectivity in the synthesis of octahydropyrido[1,2-a]pyrimidinones. The cyclization with acetophenone is characterized by the regiospecific generation of these bicycles. The presence of three chiral centers in the synthesized bicycles, depending on the alkyl substituent, causes the formation of two to four diastereomers, the structure of which has been determined with ¹H, ¹⁹F, ¹³C, 2D ¹H-¹³C HSQC/HMBC, ¹H-¹H COSY/NOESY NMR and X-ray diffraction analysis.

The synthesis of trifluoromethylated isothiazolium thiocyanates and 4-thiocyanato-2,5-dihydrofurans is presented through hydrothiocyanation/cyclization of CF₃-iminopropargyl alcohols using NaSCN in AcOH/MeCN. The formation of the two products can be explained by different directions of cyclization of the primary adducts of thiocyanic acid at the triple bond - vinyl thiocyanates. This protocol features simple operating, readily prepared starting materials and occurs under relatively mild conditions.

In this paper, the mechanism of the hydroxy(tosyloxy)iodobenzene (HTIB)-mediated conversion of chalcones (α,β-unsaturated carbonyl compounds) to ditosyloxy ketones is investigated. Here, at β-carbon of the chalcone, an aryl group with a para-substituent is present. Our study focuses on investigating the effect of different nature of para-substituents on the reaction mechanism. The substituents considered in the study include -OCH₃, -SCH₃, -Cl and -NO₂ groups. For these chalcones, different possible pathways at various steps during the reaction are investigated leading to formation of α,β-ditosyloxy ketones and β,β-ditosyloxy ketones. It is found that the mechanism for the formation of α,β-ditosyloxy ketone involves only electrophilic addition of HTIB, and the mechanism is the same for all studied chalcones, irrespective of whether an electron-donating or electron-withdrawing substituent is present on the aryl ring. However, the detailed mechanism for the formation of β,β-ditosyloxy ketones is different and depends on the nature of the substituent. Broadly, the formation of β,β-ditosyloxy ketones involves electrophilic addition followed by 1,2-aryl migration. Our study shows that the presence of an electron-donating group on the migrating aryl ring favours the formation of β,β-ditosyloxy ketones while in case of electron-withdrawing groups, there are nearly equal chances of the formation of α,β-ditosyloxy ketones and β,β-ditosyloxy ketones.

The Veratrum alkaloids constitute a class of natural products with particularly intricate polycyclic frameworks and dense stereochemistry and, thus, have stood long as benchmarks in chemical synthesis. Recently, these steroid alkaloids gained popularity as challenging targets in total synthesis, with a clear shift toward convergent strategies. Not only do these syntheses feature rapid assembly of their challenging cores through modular and strategic bond connections, but they also give a reflection on the advancement of modern synthetic methods and retrosynthetic logic. This review will cover recent syntheses, highlighting the convergence of modern strategic disconnections, stereocontrol, and late-stage functionalization for rapid access to these exceptional alkaloids, while also showcasing the evolution of the art of synthesis and its ability in meeting the demands posed by molecular complexity.

New tetra- and pentacyclic derivatives of the dibenzo[c,f][1,2]thiazepine ring system have been synthesized. The target compounds contain methylenedioxy or ethylenedioxy substituents linked to the benzene ring. The key step for the construction of the ring systems has been implemented by an intramolecular Friedel-Crafts cyclization. Altogether eight new ring systems are described here, five of them are also characterized by single-crystal X-ray diffraction.

Herein, we report a concise chemoenzymatic synthesis of the cardenolide rhodexin A in 9 steps and the first protecting-group-free synthesis of its aglycone sarmentogenin in 7 steps from 17-deoxycortisone. The synthesis features a scalable enzymatic C₁₄-H α-hydroxylation, a Bestmann ylide-enabled one-step construction of the butenolide motif, a late stage Mukaiyama hydration, and a stereoselective C11 carbonyl reduction.

Various 5-arylidene derivatives were prepared via a Knoevenagel condensation-type reaction of aromatic/heteroaromatic aldehydes with rhodanine or thiazolidine-2,4-dione (TZD) catalyzed by EDA/AcOH under microwave heating. This convenient methodology is broad in scope (49 different products were obtained), delivers excellent yields (up to 99%), and requires low catalyst loading (10 mol %). This new approach was successfully applied to the synthesis of eight novel imidazo[1,2-a]pyridine-thiazolidinone hybrids in good to excellent yields (66-99%). A spectroscopic study of compounds 3n and 4n was carried out using torsion angle analysis and ¹³C NMR chemical shift calculations to evaluate the absence of expected signals in the NMR spectra of these compounds. Their photophysical properties were also assessed, confirming a preference for a fluorescence mechanism via an ICT (intramolecular charge transfer) process.

This study establishes an efficient solid-phase strategy for the total synthesis of segetalins A-H, J and K (1-10), bioactive cyclopeptides isolated from Vaccaria segetalis. Linear precursors were assembled on cost-effective 2-chlorotrityl chloride resin via Fmoc-SPPS, followed by PyBOP-mediated head-to-tail cyclization in DMF (10^-3 M). After RP-HPLC purification, all cyclopeptides were obtained in 45-70% isolated yields. Structural identities were confirmed by HRESIMS, NMR, and HPLC (>95% purity). Circular dichroism (CD) spectroscopy revealed distinct secondary structures, including β-sheets (1, 2, 3, 4, 7, 8, 10) and α-helical elements (5, 6). This scalable methodology overcomes limitations of prior syntheses, enabling biological evaluation.

Anion removal from aqueous solutions remains a major challenge due to the strong hydration of anions. Here, we report the preparation of silica gel functionalized with covalently anchored bambusuril macrocycles. In aqueous solution, this material efficiently sorbs dicyanoaurate(I), the key anion in gold mining, even in the presence of competing dicyanoargentate(I) anions. We also examine the recyclability of the material and assess its stability in organic solvents, comparing its performance with that of a previously developed material containing noncovalently bound bambusuril.

Over the past two decades, organocatalyzed visible-light-mediated radical chemistry has significantly influenced modern synthetic organic chemistry. In particular, dual catalysis combining N-heterocyclic carbenes (NHCs) with organophotocatalysts (e.g., 4CzIPN, eosin Y, rhodamine, 3DPAFIPN, Mes-Acr-Me⁺ClO₄ ^-) has emerged as a powerful photocatalytic strategy for efficiently constructing a wide variety of carbonyl compounds via radical cross-coupling processes. This cooperative organic dual catalysis has great potential in medicinal, pharmaceutical, and materials science applications, including the development of organic semiconductors and polymers. In recent years, NHC-involved photocatalysis has attracted considerable attention in synthetic organic chemistry, and particularly in the late-stage functionalization of bioactive compounds, drugs, and natural products. This review highlights recent advances in NHC-organophotoredox dual catalysis, focusing on methodology development, mechanistic insights, and reaction scope for synthesizing carbonyl compounds and pharmaceutically relevant intermediates. Moreover, this catalytic system operates under green and sustainable conditions, tolerating a broad range of functional groups and substrate scope, and utilizes low-cost, atom-economical, non-toxic starting materials.