Base-Mediated Cyclocondensation of Salicylaldehydes and 2-Bromoallyl Sulfones for the Synthesis of 3-Sulfonylchromene Derivatives and Their Regioselective Friedel–Crafts Heteroarylation Reactions

A formal vinylic substitution reaction for the synthesis of α,β-unsaturated enol esters and their anticancer potential

Arylsulfonyl group-bearing α,β-unsaturated enol esters were readily assembled via the Cs2CO3-mediated union of 2-bromoallyl sulfones and cinnamic acids. The overall transformation is equivalent to an sp2 carbon-oxygen coupling reaction, and therefore constitutes a formal vinylic substitution. Several of the products display promising levels of antiproliferative activities higher than that of the anticancer drug carboplatin. Thiophenol reacted with 2-bromoallyl sulfones under identical conditions to afford α-thiophenyl-α'-tosyl acetone via an apparent aerial oxidation.

Visible-Light Induced Radical Addition-Elimination Reaction for Constructing Allylic Sulfones from Sulfonyl Chlorides and Allyl Bromides

Allyl sulfones are commonly present in bioactive compounds and organic building blocks. This work introduces a photocatalytic radical addition-elimination reaction involving readily accessible sulfonyl chlorides and allyl bromides. It delivers structurally diverse allylic sulfones in moderate to excellent yields, showcasing a high tolerance to functional groups. Notably, this method operates under mild reaction conditions without the need for oxidants, stoichiometric reducing metals, or additives.

Hybrid Heterocycles: Ag(I)-Catalyzed C-C/C-N/C-O Coupled Cascade Dual Cyclization to Valuable Indolo-4H-indolones and Indolo-4H-chromenes

Herein, we report a highly efficient Ag(I)-catalyzed indolyzation with Friedel-Crafts alkylation through a cascade cyclization strategy for accessing valuable hybrid heterocycles for the first time. This general strategy consists of forming four C-C/C-N/C-O bonds toward dual annulation reactions of 2-alkynylanilines with methyl benzoate-2-carboxaldehydes and aromatic amines, as well as with salicylaldehydes and malononitrile. Variably substituted new indolo-4H-phthalimidines and indolo-4H-chromenes were synthesized with excellent yields (85-93%) under mild reaction conditions.

Tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides for the synthesis of 4-phosphorylated 4H-chromenes

A Hg(OTf)2-catalyzed tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides is presented. This protocol provides a new and supplementary approach for the preparation of 4-phosphorylated 4H-chromenes in good yields (up to 99%). In addition, this domino reaction allows the successful construction of two new C-P and C-O bonds in a one-pot operation.

Efficient Synthesis of 3-Sulfonyl-2-sulfonylmethyl-2H-chromenes via Tandem Knoevenagel Condensation/Oxa-Michael Addition Protocol

An organocatalytic [4 + 2] cascade annulation of salicylaldehydes and 1,3-bisarylsulfonylpropenes has been developed. This protocol enables the efficient and straightforward synthesis of a new series of 3-sulfonyl-2-sulfonylmethyl-2H-chromenes that are useful for exploring pharmacologically valued compounds. Further reductive modifications result in 3-desulfonylated chromene or chromane derivatives. This protocol can be expanded to the synthesis of 3-sulfonyl-2-sulfonylmethyl 1,2-dihydroquinoline.

Rapid synthesis of azepinoindole derivatives from tryptamine sulfonamides and bromoallyl sulfones via an acid-mediated cyclization and rearrangement

The azepinoindole framework present in natural alkaloids such as subincanadine F, ibogaine and catharanthine was formed in a novel acid-promoted cyclization-rearrangement of tryptamine-derived N-sulfonyl enamines. The latter were conveniently prepared via a cesium carbonate mediated formal vinylic substitution reaction of 2-bromoallyl sulfones (allenyl sulfone surrogate) and tryptamine sulfonamides. The azepinoindole forming cyclization-rearrangement involves the initial generation of a six-membered tetrahydro-β-carboline derivative. The steric bulk of the N-sulfonyl group on tryptamine plays an important role in deciding the reaction outcome.

Base-mediated 1,3-dipolar cycloaddition of pyridinium bromides with bromoallyl sulfones: a facile access to indolizine scaffolds

An expedient and transition-metal-free synthetic strategy has been developed for the construction of substituted indolizines from a unique combination of pyridinium salts and 2-bromoallyl sulfones. This approach does not compromise with the diverse substitutions on both the pyridinium salts and 2-bromoallyl sulfones. Wide substrate scope, operational simplicity, milder reaction conditions and good to moderate yields are the merits associated with the current approach. Moreover, this method provides two products which are amenable for the generation of a library of key indolizine building blocks.

Regioselective synthesis of arylsulfonyl heterocycles from bromoallyl sulfones via intramolecular Heck coupling reaction

Indoles, benzofurans and benzosultams endowed with arylsulfonyl groups were prepared in two steps from 2-bromoallyl sulfones. ortho-Halosulfonamides and ortho-iodophenol reacted with 2-bromoallyl sulfones in the presence of cesium carbonate to furnish products resulting from a formal vinylic substitution reaction. Palladium-catalyzed intramolecular Heck reaction of these adducts furnished sulfonylated indoles, benzosultams and benzofurans. Isomerization of the double bond participating in the Heck reaction under basic conditions led to the formation of two isomeric products in two cases. Conditions for selectively accessing each of the regioisomeric indoles were developed.

Direct synthesis of ortho-methylthio allyl and vinyl ethers via three component reaction of aryne, activated alkene and DMSO

A transition-metal free synthetic strategy for the direct synthesis of ortho-methylthio allyl and vinyl ethers via cascade three-component coupling of aryne, activated alkene and DMSO.

Recent developments in the chemistry of allenyl sulfones

Allenyl sulfones are versatile building blocks for the construction of various acyclic, carbocyclic and heterocyclic motifs. Recent developments in the preparation and synthetic applications of allenyl sulfones are summarised.

Gold-catalysed regioselective cascade cycloisomerisation reactions of aza-enediynes for the synthesis of substituted benzoisoquinoline derivatives

A facile, regioselective, gold-catalysed cascade cycloisomerisation of easily assembled aza-enediynes to afford dihydrobenzo[f]isoquinoline derivatives is reported.

A cascade process for the synthesis of ortho-formyl allyl aryl ethers and 2H-chromen-2-ol derivatives from arynes via trapping of o-quinone methide with an activated alkene

A transition-metal free synthetic strategy for the direct synthesis of ortho-formyl substituted allyl aryl ethers and 2H-chromen-2-ol derivatives via a cascade three-component coupling of arynes, activated alkene and N,N-dimethylformamide.

Synthesis of Diversely Functionalized 2 H-Chromenes through Pd-Catalyzed Cascade Reactions of 1,1-Dibromoolefin Derivatives with Arylboronic Acids

In this work, an unprecedented synthesis of (2 H-chromen-2-ylidene)acetates and (2 H-chromen-2-ylidene)ethanones with controlled stereoselectivity via Pd-catalyzed cascade reactions of 3-(2-(2,2-dibromovinyl)phenoxy)acrylates or 3-(2-(2,2-dibromovinyl)phenoxy)enones with aryl boronic acids has been established. This protocol combines two C-C bond forming reactions (an intermolecular Suzuki coupling followed by an intramolecular Heck coupling) in one pot under the catalysis of the same catalyst. Compared with literature methods for the preparation of 2 H-chromene derivatives, it has advantages such as easily obtainable or commercially available substrates, diverse substitution pattern of products, simple procedure, and excellent stereoselectivity. Interestingly, this cascade reaction could distinguish the subtle difference of the electron-withdrawing capacity and the size of various functional groups and thus resulted in a different chemoselectivity. In addition, the utility of the (2 H-chromen-2-ylidene)acetate thus obtained was showcased by its facile transformation into the synthetically and photophysically significant 3 H-xanthen-3-one derivative.

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

In strong Brønsted acids (CF₃SO₃H, FSO₃H, D₂SO₄), (arysulfonyl)allenes (ArSO₂–CR¹=C=CR²R³) and (arylsulfinyl)allenes (ArSO–CR¹=C=CR²R³) undergo cyclization into the corresponding stable 1,2-oxathiolium ions, which were studied by means of NMR and DFT calculations. Quenching of solutions of these cations with low nucleophilic media, aqueous HCl, leads to their deprotonation with a stereoselective formation of (arysulfonyl)butadienes (for instance, ArSO₂–CR¹=C–C(Me)=CH₂, for R² = R³ = Me, yields of 87–98%). Reactions of (arysulfonyl)allenes in the system TfOH (0.1 equiv)–HFIP (hexafluoropropan-2-ol) followed by hydrolysis give rise to allyl alcohols (ArSO₂–CR¹=CH–C(OH)R²R³, yields of 78–99%). Reflux of solutions of (arysulfonyl)allenes in the presence of TfOH (1 equiv) in 1,2-dichlorobenzene leads to the cyclization into thiochromene 1,1-dioxides in high yields. Under the action of TfOH or AlX₃ (X = Cl, Br) followed by hydrolysis of reaction mixtures, (arylsulfinyl)allenes give allyl alcohols (ArSO₂–CR¹=CH–C(OH)R²R³). Plausible reaction mechanisms have been proposed for all studied reactions.

Elemental sulfur accelerated the reactivity of the 3-position of indole for the construction of chromeno[2,3-b]indoles

Elemental sulfur not only acted as an additional oxidant but also facilitated the reactivity of the 3-position of indole to construct chromeno[2,3-b]indoles.

Practical Synthesis of Chromeno[2,3-b]indole Skeleton via an Aldehyde Group Insertion/Aromatization Strategy

The synthesis of chromeno[2,3-b]indole from simple starting materials remains a demanding process. Herein, 2-bromoindole undergoes nucleophilic attack from salicylaldehyde, followed by intramolecular insertion of an aldehyde group and aromatization to generate the desired chromeno[2,3-b]indoles. Moreover, various functional groups were tolerated and a gram-scale synthesis of the product could be achieved under the optimized condition.

One-pot three-component protocol for the synthesis of indolyl-4H-chromene-3-carboxamides as antioxidant and antibacterial agents

A series of newly synthesized 4-(1H-indol-3-yl)-2-methyl-N-phenyl-4H-chromene-3-carboxamide derivatives catalyzed by 1,4-Diazabicyclo [2.2.2]octane (DABCO) (30 mol%) at room temperature.

Facile synthesis of 4H-chromene derivatives via base-mediated annulation of ortho-hydroxychalcones and 2-bromoallyl sulfones

The cesium carbonate-mediated reaction of 2-bromoallyl sulfones and ortho-hydroxychalcones furnished 3-arylsulfonyl-4H-chromene derivatives in 58–67% yield (18 examples). 2-Bromoallyl sulfones functioned as synthetic surrogates for allenyl sulfones in the reaction.

The facile synthesis of 1-benzoazepine derivatives via gold-catalyzed regioselective cycloisomerization reactions of N-(o-alkynylaryl)-N-vinyl sulfonamides

Gold-catalyzed, regioselective cycloisomerization of N-(o-alkynylaryl)-N-vinyl sulfonamides afforded high yields of 2-sulfonylmethyl-1-benzoazepine derivatives.

Ligand-controlled gold-catalyzed cycloisomerization of 1,n-enyne esters toward synthesis of dihydronaphthalene

We describe herein a gold-catalyzed rearrangement of propargyl esters followed by allene–ene cyclization to afford substituted bicyclic [4.4.0] dihydronaphthalene compounds.