Domino Approach to Heterocycles-Based Unsymmetrical Triarylmethanes through Heteroannulation of 2-(2-Enynyl)-pyridines with Enaminones

Herein, we report a copper-catalyzed protocol to access unsymmetrical triarylmethanes containing both indolizine and the chromone scaffolds in the same molecule via a 5-endo-dig cyclization of 2-(2-enynyl)-pyridines followed by reaction with 2-hydroxyaryl enaminones. A variety of 2-hydroxyaryl enaminones and 2-(2-enynyl)-pyridines were subjected to reaction under the optimal reaction conditions, and the respective triarylmethanes were obtained in good to excellent yields.

Transition-Metal-Free Synthesis of 3-Acyl Chromones by the Tandem Reaction of Ynones and Methyl Salicylates

A facile and effective tandem reaction of ynones and methyl salicylates was developed to obtain a broad range of 3-acyl chromones in moderate-to-excellent yields. This protocol underwent a Michael addition and cyclization process, which exhibited easily accessible substrates, broad substrate scope, and high regioselectivity under mild and transition-metal-free conditions. Moreover, gram-scale reaction and further chemical transformation of the products were also further studied.

Phosphine-Catalyzed Synthesis of 3-Allyl-4-pyrones by the Tandem Reaction of Diynones and Allylic Alcohols

A simple and effective tandem reaction of diynones and allylic alcohols was developed to afford functionalized 3-allyl-4-pyrones in moderate to excellent yields. This protocol underwent a Michael addition─Claisen rearrangement─O-cyclization process, which exhibited broad substrate tolerance, high regioselectivity, and atom economy under a metal-free condition. Moreover, functional transformation of the products was also further studied.

Access to Chiral Chromenones through Organocatalyzed Mannich/Annulation Sequence

Herein we report an efficient and practical method to access chiral chromenones bearing one α-amino stereogenic center in the β position of the carbonyl group. The quinine-derived squaramide could efficiently promote Mannich/cycloketalization/dehydration tandem reactions between 1-(2-hydroxyaryl)-1,3-diketones and functionalized imines generated in situ, providing a wide range of chiral chromenones with propargylamine or α-amino ester moieties with good results (54 examples, up to 98% ee).

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions

The synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via a sequential [3+2] cycloaddition/ring-opening/O-arylation reaction under transition metal- and additive-free conditions is reported.

Selective Mono-allylation of 1,3-Diketones and Their Use in the Synthesis of 3-Allyl Chromones and Benzannulated 6,5-Bicyclic Ketals

The selective mono-allylation of 1,3-diketone containing compounds is described. The reaction proceeds under mild reaction conditions and in moderate to high yield (66-99 %). Using this procedure to access the key mono-allylated intermediate, the hitherto difficult to access 3-allyl chromones were synthesized in excellent yield (87-98 %). Finally, the utility of this newly developed procedure was showcased through the rapid synthesis of the scaffold of the xyloketal family of natural products.

An effective preparation of both 1,3-diketones and nitriles from alkynones with oximes as hydroxide sources

An effective phosphine-catalyzed protocol has been established for the syntheses of 1,3-diketones and nitriles from alkynones with oximes as hydroxide surrogates. This method features the use of a phosphine catalyst, compatibility with various functional groups and ambient temperature, which makes this approach very practical. A plausible mechanism was proposed.

Facile synthesis of 9H-pyrrolo[1,2-a]indoles via Brønsted acid catalyzed cascade reactions

A Brønsted acid system promotes the Friedel–Crafts alkenylation/1,6-addition/condensation cascade reaction of ynones with indoles to access 9H-pyrrolo[1,2-a]indoles.

An efficient tandem synthesis of chromones from o-bromoaryl ynones and benzaldehyde oxime

A transition-metal-free approach was developed to synthesize chromones from o-bromoaryl ynones and benzaldehyde oxime by sequential C–O bond formation.

Transition-metal-free insertion reactions of alkynes into the C–N σ-bonds of imides: synthesis of substituted enamides or chromones

Transition-metal-free insertion of ynones into the C–N σ-bonds of imides for the chemo-selective synthesis of chromones or enamides.

Transition-metal-free synthesis of 3-sulfenylated chromones via KIO3-catalyzed radical C(sp2)-H sulfenylation

The reactions between o-hydroxylphenyl-functionalized enaminones and sulfonyl hydrazines providing 3-sulfenylated chromones via domino chromone ring construction and C(sp²)-H bond sulfenylation have been achieved under transition-metal-free conditions by using KIO₃ as the only catalyst.

Synthesis of Chromones from 1,1-Diacylcyclopropanes: Toward the Synthesis of Bromophycoic Acid E

A tandem deprotection-cyclization reaction of 1,1-diacylcyclopropanes is described which allows rapid access to structurally diverse 2,3-disubstituted chromones in good yields, and with straightforward purification. The utility of this reaction is showcased by the construction of the potent antibacterial marine natural product bromophycoic acid E scaffold.

The base-promoted synthesis of multisubstituted benzo[b][1,4]oxazepines

A variety of substituted benzo[b][1,4]oxazepines have been prepared via base-promoted intramolecular O-arylation from N-(2-haloaryl)enaminones under metal-free conditions.

Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N(1)-Alkyne-1,2-diamines

A one-pot protocol for the diversity oriented synthesis of two N-polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N(1)-alkyne-1,2-diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6-endo-dig cyclization, 1,2-migration with ring expansion, and re-aromatization), or diazepine and triazole rings through 1,3-dipolar cycloaddition.

Base-Promoted N-Pyridylation of Heteroarenes Using N-Propargyl Enaminones as Equivalents of Pyridine Scaffolds

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using N-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H2O as the sole byproduct.

Metal-free catalytic cascade to chromones: direct coupling of salicylaldehydes and activated alkynes triggered by aryloxyl radicals

The first intermolecular addition reaction of aryloxyl radicals to CC bonds was disclosed, which can afford biologically important chromonsviaa PhNMe₃I-catalyzed direct coupling of salicylaldehydes and activated internal alkynes in only one step.

Cleavage of the C–C triple bond of ketoalkynes: synthesis of 4(3H)-quinazolinones

A novel strategy to 4(3H)-quinazolinones from ketoalkynes and o-aminobenzamides through C–C triple bond fragmentation and two C–N bond formations under external oxidant and metal free conditions.

A metal-free synthesis of diaryl-1,2-diketones by C–C triple bond cleavage of alkynones

A novel and environmentally benign protocol for diaryl-1,2-diketones was developed.