Stereoselective hetero-Diels-Alder reaction of 3-(trifluoroacetyl)chromones with cyclic enol ethers: synthesis of 3-aroyl-2-(trifluoromethyl)pyridines with ω-hydroxyalkyl groups

3-(Trifluoroacetyl)chromones undergo heterodiene cycloaddition to 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild conditions, producing novel fused pyrans with high stereoselectivity and in good yields. These pyrans were transformed into functionalized pyridines on treatment with ammonium acetate in ethanol. The structures of the endo-cycloadducts were established by ¹H NMR spectroscopy and X-ray diffraction analysis.     

Successive Michael reactions on chromone derivatives with dimethyl 1,3-acetonedicarboxylate: one-pot synthesis of functionalized benzophenones, benzo[c]chromones and hydroxybenzoylfuroates

Chromones were reacted with dimethyl acetonedicarboxylate in the presence of DBU in THF at room temperature to furnish good yields of products, their structure depending on the substituent at 3-position. Unsubstituted chromones lead to methyl 7-hydroxy-6-oxo-6H-benzo[c]chromone-8-carboxylates 2, whereas by using 3-bromochromone, the methyl furoate 3c along with the unexpected furylcyclopropyl-chromene carboxylate 4c was isolated. Finally, from 3-formyl-chromones functionalized benzophenones 5 were isolated, in good yields. Plausible mechanisms are proposed.     

An efficient fluoride-mediated O-arylation of sterically hindered halophenols with silylaryl triflates under mild reaction conditions

The reaction between 2,6-dihalophenols and 2-(trimethylsilyl)aryl triflates in the presence of CsF using acetonitrile as solvent at room temperature led to the formation of functionalized diaryl ethers in very good yields.     

Synthesis of Functionalized 1‐Azadienes by Reaction of 2,6‐Dimethylphenyl Isocyanide and Acetylenic Esters in the Presence of CH Acids

The adducts produced in the reaction between 2,6‐dimethylphenyl isocyanide and acetylenic esters were trapped by 3‐chloroacetylacetone, dialkyl 2‐chloromalonates, or dimethoxy methoxymalonate to produce highly functionalized 1‐azadienes in good yields.     

Synthesis of functionalized chromones via organocatalysis

A facile and versatile organocatalytic approach to access 2-substituted and 2,3-disubstituted chromone derivatives under mild conditions was developed, which was effectively catalyzed by novel proline phenylsulphonylhydrazide or pyrrolidine. As a result, diversely functionalized chromones were obtained in up to 99% yield. In addition, further modification of the corresponding chromones afforded novel polycyclic chromones.     

3-(2-二唑啉基)-色酮类化合物的合成研究

报道了取代的邻羟基苯乙酮(1a～1e)经Vilsmeier-Haack反应一步制得3-醛基色酮(2a～2e),2a～2e与取代的芳酰肼(3a～3c)缩合制得15个酰腙类化合物(4a～4o),4a～4o在醋酸酐作用下关环得15个3-(2-苝二唑啉基)-色酮(5a～5o),并通过元素分析,IR,~1H NMR和MS诺数据确证了上述化合物的结构。     

3-(2-卓二唑啉基) - 色酮类化合物的合成研究

报道了取代的邻羟基苯乙酮(1a～1e)经Vilsmeier-Haack反应一步制得3－醛基色酮(2a～2e),2a～2e与取代的芳酰肼(3a～3c)缩合制得15个酰腙类化合物(4a～4o),4a～4o在醋酸酐作用下关环得15个3-(2-卓二唑啉基)-色酮(5a～5o),并通过元素分析,IR,^1^HNMR和MS谱数据确证了上述化合物的结构。     

Reactions of 3-(polyfluoroacyl)chromones with hydroxylamine. The first synthesis of 3-cyano-2-(polyfluoroalkyl)chromones

Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine proceeds via nucleophilic 1,4-addition followed by opening of the pyrone ring and subsequent cyclization to 4-(polyfluoroalkyl)-4H-chromeno[3,4-d]isoxazol-4-ols in good yields. On treatment with trifluoroacetic acid, the isoxazole ring of this annulated heterocyclic system opens to give 3-cyano-2-(polyfluoroalkyl)chromones. Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine hydrochloride occurs only at the carbonyl carbon atom connected to the R^F group to give the corresponding oximes in low yields.     

Diversity-oriented synthesis of 3-iodochromones and heteroatom analogues via ICl-induced cyclization

The ICl-induced cyclization of heteroatom-substituted alkynones provides a simple, highly efficient approach to various 3-iodochromones and analogues. This process is run under mild conditions, tolerates various functional groups, and generally provides chromones in good to excellent yields. Subsequent palladium-catalyzed transformations afford a rapid increase in molecular complexity and a convenient preparation of a wide range of functionally substituted chromones, furans, and polycyclic compounds. Iodothiochromenones and iodoquinolinones are also prepared by similar ICl-induced cyclizations.     

Accelerating lead optimization of chromone carboxamide scaffold throughout microwave-assisted organic synthesis

Microwave irradiation offers a considerable advantage over conventional synthesis with rate enhancements and cleaner reactions. Accordingly, a new microwave-assisted method for the synthesis of functionalized chromones was developed allowing the obtention of a library of chromone carboxamides. The method has been shown to present several advantages including operational simplicity, good performance, significant reduction in reaction time, less formation of by-products, and easier work-up.     

Ammonium iodide-mediated regioselective chalcogenation of chromones with diaryl disulfides and diselenides

A metal-free method for the synthesis of 3-chalcogenyl-chromones/quinolones from chromones/quinolones and diorganyl dichalcogenides using ammonium iodide under air was developed. This approach allowed the preparation of a wide range of 3-selenyl- and 3-sulfenyl-chromones/quinolones in good to excellent yields.     

Indium-catalyzed radical reductions of organic halides with hydrosilanes

The In(OAc)3-catalyzed reaction of bromo- and iodoalkanes with PhSiH3 in THF at 70 degrees C gave dehalogenated alkanes in good to high yields. In the presence of Et3B and air, the reduction proceeded smoothly at 30 degrees C. When 2,6-lutidine and air were used as additives, the In(OAc)3-catalyzed system enabled an efficient reduction of simple and functionalized iodoalkanes in EtOH. Catalytic use of GaCl3 was found to be effective in the reduction of haloalkanes with poly(methylhydrosiloxane) (PMHS). These catalytic reductions probably involve a radical chain mechanism in which indium or gallium hydride species work as the actual reductants.     

Catalytic enantioselective allylation of aldehydes using β-amido functionalized allylstannanes with chiral In(OTf)3/i-Pr-pybox complexes

The enantioselective allylation of aldehydes using a variety of β-amido functionalized allyltributylstannanes proceeded smoothly with good to high yields and enantioselectivities in the presence of 10 mol % of a chiral catalytic complex prepared from In(OTf)₃ and 2,6-bis[(S)-4-isopropyloxazolin-2-yl]pyridine {(S)-i-Pr-pybox}, providing the corresponding chiral γ-hydroxy amides.     

Diastereoselective Nucleophilic Ring‐Opening Reactions of 2,6‐Diazasemibullvalenes for the Synthesis of Diverse Functionalized Δ1‐Bipyrroline Derivatives

Nucleophilic ring‐opening reactions of 2,6‐diazasemibullvalenes (NSBVs) were investigated. Different types of nucleophile (alcohols, phenols, thiols, carboxylic acids, water, enols, amines, indoles, metal‐halide salts, sodium azide, organozinc compounds, lithium alkynethiolate, and sulfoxonium ylides) were used to afford diverse functionalized Δ¹‐bipyrroline derivatives in good yields with high regio‐ and diastereoselectivity. Most of the reactions featured milder conditions and higher reactivity relative to those for common aziridine derivatives, probably because of the rigid ring system and substitution patterns of NSBVs.     

Improved synthesis of functionalized mesogenic 2,6-bisbenzimidazolylpyridine ligands

A versatile one-pot synthetic platform for the preparation of a range of functionalized 2,6-bisbenzimidazolylpyridine (Bip) derivatives is presented. This protocol significantly reduces the cost and time of previous synthetic routes, while facilitating scale up to multi-gram quantities in good yields (63-90%). The previous synthetic methodology was improved through judicious choice of the reducing agent and solvent in the reduction/ring-closing step. Via this platform, we also successfully accessed a mesogenic Bip ligand and herein report initial liquid crystalline properties of this derivative.     

Domino reactions of 1,3-bis-silyl enol ethers with benzopyrylium triflates: efficient synthesis of fluorescent 6H-benzo[c]chromen-6-ones, dibenzo[c,d]chromen-6-ones, and 2,3-dihydro-1H-4,6-dioxachrysen-5-ones

The condensation of 1,3-bis-silyl enol ethers with benzopyrylium triflates, generated in situ by the reaction of chromones with Me3SiOTf, afforded functionalized 2,3-dihydrobenzopyrans; treatment of the latter with NEt3 or BBr3 resulted in a domino retro-Michael-aldol-lactonization reaction and the formation of a variety of 7-hydroxy-6H-benzo[c]chromen-6-ones. The hydroxy group was functionalized by using Suzuki cross-coupling reactions. The methodology reported was applied to the synthesis of the natural product autumnariol and a new fluorescence dye, which exhibits promising optical properties. 2,3-Dihydro-1H-4,6-dioxachrysen-5-ones were prepared by condensation of chromones with 1,3-bis-silyl enol ethers containing a remote chloride group, domino retro-Michael-aldol-lactonization, and an intramolecular Williamson reaction.     

Direct synthesis of tetrahydropyrans via one-pot Babier-Prins cyclization of allylbromide with carbonyl compounds promoted by RTILs BPyX/SnX′2 or BBIMBr/SnBr2

Tetrahydropyran compounds can be directly synthesized from allylbromide and carbonyl compounds by means of one-pot Babier-Prins cyclization promoted by BPyX/SnX′₂ or BBIMBr/SnBr₂ complex (functionalized RTILs) under solvent-free conditions. 2,6-Homo-bissubstituted- and 2,6,6-trisubstituted, especially 6-(spirocycloalkyl)-, tetrahydropyran compounds can be prepared in good yields.     

Stereoselective hetero-Diels–Alder reaction of 3-(polyfluoroacyl)chromones with enol ethers. Novel synthesis of 2-R-containing nicotinic acid derivatives

3-(Polyfluoroacyl)chromones undergo heterodiene cycloaddition to 3,4-dihydro-2H-pyran, 2,3-dihydrofuran and ethyl vinyl ether under mild conditions, producing novel fused pyrans with high stereoselectivity and in good yields. Some of these pyrans were transformed into 2-R^F-containing pyridines on treatment with ammonium acetate in ethanol.     

Reaction of polyhaloalkyl-substituted chromones, pyrones, and furanones with salicylaldehydes as a direct route to fused 2H-chromenes

Polyhaloalkyl-substituted chromones, gamma-pyrones, and beta-furanones react with salicylaldehydes in the presence of piperidine to give a wide variety of fused 2H-chromenes in good yields. This novel annulation reaction presumably proceeds by a tandem intermolecular oxa-Michael addition and subsequent intramolecular Mannich condensation.     

Tandem [5+1] annulation-isocyanide cyclization: efficient synthesis of hydroindolones

A new strategy for the rapid construction of functionalized reduced indoles starting from activated methylene isocyanides and 1,5-dielectrophilic 5-oxohepta-2,6-dienoates (and their equivalents) through a [5+1] annulation-isocyanide cyclization cascade under basic conditions has been developed. This strategy allows the synthesis of polysubstituted dihydroindolones and tetrahydroindolones in high to excellent yields under extremely mild conditions in a single step.