10.1039/c39800000884
The research investigates intramolecular nucleophilic substitutions of coordinated aryl halides to prepare chromans. The key chemicals involved include 3-(0-fluorophenyl)propan-1-ol, chromium tricarbonyl complexes, (η?-benzene)(+ethyl-tetramethylcyclopentadienyl)rhodium(III) cation, potassium t-butoxide, and boron trifluoride-ether. The study found that coordination with a chromium tricarbonyl residue significantly enhances the rate of intramolecular nucleophilic substitution. The hexafluorophosphate(V) salt of the complexed rhodium(III) cation was also used to catalyze the cyclizations of fluoro alcohols to chromans under mild conditions. However, attempts to use these systems for the preparation of five-membered oxygen heterocycles were unsuccessful, likely due to the strain associated with the bicyclic intermediate.
10.1002/anie.201600379
The research aims to develop a highly enantioselective method for synthesizing chiral 1,4-benzodioxanes, 1,4-benzooxazines, and chromans, which are important structural units in many bioactive natural products and drugs. The study focuses on using palladium-catalyzed alkene aryloxyarylation reactions, with key chemicals including 2-((2-methylallyl)oxy)phenol (1a), various aryl halides such as bromobenzene (2a), and chiral monophosphorus ligands like L4 and L5. The researchers optimized the reaction conditions, finding that a strong base like NaOtBu and a solvent like hexafluorobenzene (C6F6) enhanced both yield and enantioselectivity. The method demonstrated high yields (up to 90%) and excellent enantioselectivity (up to 95% ee) for a range of substrates, including those with different aryl and heteroaryl groups. The study concludes that the chiral monophosphorus ligands L4 and L5 are crucial for the high reactivity and enantioselectivity of the transformations. The findings not only provide a practical route for synthesizing these chiral compounds but also offer valuable insights into the design of better catalytic systems for similar transformations.
10.3998/ark.5550190.p008.801
The research aims to develop a simple and efficient method for synthesizing 2-aryl-3-nitro-2H-chromenes and 2,3,4-trisubstituted chromanes, which are important building blocks in organic synthesis and pharmaceuticals. The study employs salicylaldehydes and β-nitrostyrenes as starting materials, using a combination of pyrrolidine and benzoic acid as catalysts to achieve tandem oxa-Michael-Henry reactions in refluxing ethanol, yielding 2-aryl-3-nitro-2H-chromenes with up to 83% yield. These chromenes are then reacted with acetone under the same catalytic combination in brine to produce 2,3,4-trisubstituted chromanes with yields up to 86% and excellent stereoselectivities. The structures of the synthesized compounds are confirmed by X-ray single crystal diffraction analysis. Additionally, the reductive amination of a suitable 2,3,4-trisubstituted chromane with Zn/HOAc yields a fused tricyclic amine in 92% yield. The research concludes that this catalytic strategy is practical and efficient, offering a reliable synthesis method under mild conditions, and ongoing work is focused on exploring enantioselective synthesis using various organocatalysts.
10.1002/chem.200800210
The study explores the use of gold catalysis to synthesize various heterocycles, including chromans, dihydrobenzofurans, dihydroindoles, and tetrahydroquinolines. The researchers prepared furans containing ynamide or alkynyl ether moieties in the side chain and used gold-catalyzed transformations to achieve these syntheses at room temperature through fast reactions. The heteroatom directly attached to the intermediate arene oxides stabilized the intermediates, leading to highly selective reactions, even with mono-substituted furans. The study involved various chemicals, including lithiated furans for the introduction of side chains, oxiranes and enones for synthesis of alcohols, and dichlorovinyl ethers and toluenesulfonamides as starting points for ynamide syntheses. The gold-catalyzed reactions resulted in the formation of the desired heterocycles with good yields and selectivity, highlighting the efficiency and versatility of gold catalysis in organic synthesis.
