Pd-Catalyzed Formal [3 + 3] Heteroannulation of Allylic gem-Diacetates: Synthesis of Chromene-Based Natural Products and Exploration of Photochromic Properties

Lewis Acid-Mediated Domino Glycosylation/Cyclization of Substituted Glycals: A Stereoselective Route Toward the Synthesis of 1,2-Annulated C-Glycosides

Annulated C-glycosides are widely recognized for their natural abundance and diverse bioactivity. Traditional synthesis emphasizes stereoselective α/β C-glycoside formation, but efficiently engaging both reactive carbons of glycosyl donors remains challenging. This study introduces a novel domino sequence using substituted glycals and β-naphthols under Lewis acid catalysis, generating glycosylated intermediates that undergo cascade reactions to yield annulated 1,2-C-glycosides. The method features a broad substrate scope, mild conditions, and versatility. Notably, annulation type varies with substituted glycals, yielding [3 + 2] or [3 + 3] fused pyran systems. Control experiments and DFT calculations provide mechanistic insights into substrate-specific product formation.

Formation of 2H- and 4H-chromene Rings in Intramolecular Rauhut-Currier Reaction, Catalyzed by Lithium Selenolates

In this paper, we present the first example of using a catalytic amount of a nucleophilic seleno-organic catalyst in a tandem seleno-Michael/Michael reaction, leading to the formation of 2H/4H-chromenes. Chromenes represent a highly significant group of oxygen-containing heterocycles commonly found as structural scaffolds in a diverse range of fields such as medicinal chemistry, pharmaceutical agents, drug candidates, synthetic chemistry, and materials chemistry. Various preparation methods have been developed, utilizing different substrates in conjunction with metal catalysts, organocatalysts, Brønsted acids, bases, or Lewis acids. The synthetic utility of lithium selenolates has been demonstrated as efficient nucleophilic catalysts in the Rauhut-Currier cyclization of chalcone derivatives. This methodology allows for the synthesis of 2H- and 4H-chromenes depending on the substituents directly connected to the carbonyl group. The investigation focuses on the impact of various substituents in the aromatic fragment as well as conditions and selenolates. The scope of different starting materials was also considered.

Synthetic Approaches, Properties, and Applications of Acylals in Preparative and Medicinal Chemistry

Diesters of geminal diols (R-CH(O-CO-R')2, RR'C(OCOR″)2, etc. with R = H, aryl or alkyl) are termed acylals according to IUPAC recommendations (Rule P-65.6.3.6 Acylals) if the acids involved are carboxylic acids. Similar condensation products can be obtained from various other acidic structures as well, but these related "non-classical acylals", as one might call them, differ in various aspects from classical acylals and will not be discussed in this article. Carboxylic acid diesters of geminal diols play a prominent role in organic chemistry, not only in their application as protective groups for aldehydes and ketones but also as precursors in the total synthesis of natural compounds and in a variety of organic reactions. What is more, acylals are useful as a key structural motif in clinically validated prodrug approaches. In this review, we summarise the syntheses and chemical properties of such classical acylals and show what potentially under-explored possibilities exist in the field of drug design, especially prodrugs, and classify this functional group in medicinal chemistry.

One-Pot Three-Component Synthesis of Indolyl-4H-chromene-3-sulfonyl Fluoride: A Class of Important Pharmacophore

A one-pot, sequential three-component reaction between salicylaldehyde, indole, and 2-bromoprop-2-ene-1-sulfonyl fluoride (BPESF) has been demonstrated for the synthesis of sulfonyl fluoride substituted 4H-chromene derivatives in moderate to excellent yields (45%-94%). This one-pot sequential method features easily available starting materials, wide substrate scope, mild conditions, and great efficiency.

Synthesis of tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles via palladium-catalyzed intramolecular direct heteroarylation

We report a palladium-catalyzed intramolecular direct heteroarylation of oxazole tethered β-naphthols to access corresponding tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles. Various functional groups are well tolerated and furnished the desired products in good to excellent yields under the present reaction conditions. The scale-up reaction and synthetic utility of the resulting molecules have been demonstrated. Moreover, UV/vis absorption and fluorescence emission properties have been evaluated for these polyheterocyclic compounds.