Synthesis of pyrano[3,2-c]quinolones and furo[3,2-c]quinolones via acid-catalyzed tandem reaction of 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described. Depending mainly on the propargylic alcohol used, these tandem reactions proceed via either a Friedel–Crafts-type allenylation followed by 6-endo-dig cyclization sequence to form pyrano[3,2-c]quinolones or a Friedel–Crafts-type alkylation and 5-exo-dig ring closure sequence to afford furo[3,2-c]quinolones in moderate-to-high yields. The pyrano[3,2-c]quinolones products could be further transformed to tetracyclic 4,9-dihydro-5H-cyclopenta[lmn]phenanthridin-5-one derivatives.

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described.

Synthesis of Chiral Propargylamines, Chiral 1,2-Dihydronaphtho[2,1-b]furans and Naphtho[2,1-b]furans with C-Alkynyl N,N'-di-(tert-butoxycarbonyl)-aminals and β-Naphthols

Chiral phosphoric acid-catalyzed couplings of C-alkynyl N,N'-di-(tert-butoxycarbonyl)-aminals with β-naphthols led to chiral propargylamines in moderate to high yields with high to excellent enantioselectivity, in which the reactions underwent sequential chiral phosphoric acid-catalyzed in situ formation of N-(tert-butoxycarbonyl)-imines (N-Boc-imines) from the aminals, and 1,2-addition of β-naphthols to the N-Boc-imines. Chiral 1,2-dihydronaphtho[2,1-b]furans and naphtho[2,1-b]furans were prepared with satisfactory results when 10 mol% AgOAc and 20 mol% 2,6-lutidine or 1.2 equiv. of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were added to the resulting chiral propargylamines solution, respectively.

Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans

This review describes the progress of the last decade on the synthesis of substituted benzofurans, which are useful scaffolds for the synthesis of numerous natural products and pharmaceuticals. In particular, new intramolecular and intermolecular C-C and/or C-O bond-forming processes, with transition-metal catalysis or metal-free are summarized. (1) Introduction. (2) Ring generation via intramolecular cyclization. (2.1) C7a-O bond formation: (route a). (2.2) O-C2 bond formation: (route b). (2.3) C2-C3 bond formation: (route c). (2.4) C3-C3a bond formation: (route d). (3) Ring generation via intermolecular cyclization. (3.1) C7a-O and C3-C3a bond formation (route a + d). (3.2) O-C2 and C2-C3 bond formation: (route b + c). (3.3) O-C2 and C3-C3a bond formation: (route b + d). (4) Benzannulation. (5) Conclusion.

One-Step Regioselective Synthesis of Benzofurans from Phenols and α-Haloketones

Reported here is the direct synthesis of naphthofurans and benzofurans from readily available phenols and α-haloketones promoted by titanium tetrachloride which combines Friedel–Crafts-like alkylation and intramolecular cyclodehydration into one step. This simple protocol allows for the formation of a variety of high value naphthofurans and benzofurans within which a series of cyclic and acyclic groups are readily incorporated. This process demonstrates the advantages of high levels of regioselectivity, broad substrate scope, and moderate to excellent yields.

A ZnI2-catalyzed regioselective cascade 1,4-conjugate addition/5-exo-dig annulation pathway for one-pot access to heterobiaryl frameworks

Facile access to π-extended heterobiaryl compounds via a non-cross-coupling strategy has been achieved.

Systematic evaluation of petroleum sulfonate: polarity separation and the relationship between its structure and oil recovery properties

Petroleum sulfonate is one of the most important surfactants in the tertiary oil recovery process. However, its complex composition significantly impedes its evaluation, and the relationship between its structure and oil recovery properties is still unclear. In this study, the actives of petroleum sulfonate are subdivided into seven components, a–g, with different polarities via column chromatography. The structural information of each component is fully characterized. Moreover, the relationship between the oil recovery properties and the structure of the separated components is systematically studied. The results reveal the average relative molecular mass in the range of 560–626, average alkyl side chain containing 36–40 carbon atoms and alkyl chain containing an average of 6 branched chains is the ideal structure for enhancing oil recovery properties. Furthermore, this study provides a reliable evaluation method and reveals the relationship between the structure and oil recovery properties of petroleum sulfonate.

Petroleum sulfonate actives are efficiently separated and fully characterized, and the relationship between their structure and oil recovery properties is revealed.

Synthesis of Functionalized Benzo[b]furans via Oxidative Cyclization of o-Cinnamyl Phenols

Disclosed herein is an efficient synthetic route for the synthesis of functionalized 2-benzyl benzo[b]furans via a regioselective 5-exo-trig intramolecular oxidative cyclization of ortho-cinnamyl phenols using [PdCl₂(CH₃CN)₂] as catalyst and benzoquinone as an oxidant. Further, a sequential ortho-cinnamylation of phenols using cinnamyl alcohols catalyzed by Re₂O₇, followed by an oxidative cyclization using the above Pd catalyst, is performed. The reaction showed broad substrate scope with good to excellent yields.

Regioselective, cascade [3+2] annulation of β-naphthols (resorcinols) with Z-enoate propargylic alcohols: a novel entry for the synthesis of complex naphtho(benzo)furans

An unprecedented regioselective, first cascade [3+2] annulation process has been reported between propargylic alcohols and β-naphthols (resorcinols) for the synthesis of naphtho(benzo)furans.

n Bu4NPF6 promoted regioselective cascade synthesis of functionally embellished naphthofurans under acid, metal & solvent free conditions

Various naphthofurans were synthesised from naphthols and propargyl alcohols using a cascade benzylation/5-exo dig cyclisation/isomerization. Preliminary studies showed that some naphthofurans were excellent inhibitors for amyloid formation.

Palladium-catalyzed bisarylation of 3-alkylbenzofurans to 3-arylalkyl-2-arylbenzofurans on water: tandem C(sp3)–H and C(sp2)–H activation reactions of 3-alkylbenzofurans

A protocol involving facile sequential C(sp³)–H and C(sp²)–H activation reactions of 3-alkylbenzofurans catalyzed by Pd(OAc)₂ in the presence of pivalic acid, silver salt, and tricyclohexylphosphine ‘on water’ was developed.