Diversity-Oriented Synthesis of Spirooxindoles via Asymmetric Organocatalytic Regiodivergent Cascade Reactions

A regiodivergent strategy for the asymmetric diversity-oriented synthesis of spirooxindoles via organocatalytic cascade reactions is developed. Two regioselective pathways can be precisely controlled with different aminocatalysts in the reaction of 2-hydroxycinnamaldehydes and β,β-disubstituted 3-alkylidene oxindoles. The cascade vinylogous Michael/oxa-Michael/aldol reactions gave spiro-bridged oxindoles bearing two adjacent quaternary stereocenters, while the cascade oxa-Michael/Michael reactions gave spirooxindoles. Moreover, during the synthetic application studies, an acid-catalyzed rearrangement of spiro-bridged oxindoles was found to yield biologically important 3-alkylidene oxindoles.

InCl3/TfOH-Mediated Convenient Synthesis of 3-Alkylideneoxindoles from 2-Oxindoles with 1,3-Diones, Ketones, or Aldehydes

Two efficient and convenient methods for the synthesis of 3-alkylideneoxindoles are described in this paper. The InCl3/TfOH-mediated tandem Knoevenagel condensation-deacylation sequence of various 2-oxindoles with 1,3-diones or acetoacetate furnished 3-alkylideneoxindoles in satisfactory to excellent yields (up to >99% yield). Employing the reaction system, the condensation of 2-oxindoles with ketones or aldehydes also proceeded smoothly to produce 3-alkylideneoxindoles. This protocol can be amenable to scale up. The effect of acids on this condensation reaction and intermolecular competition experiments were investigated to understand the aspect of the reaction.

Organocatalytic Asymmetric Direct Vinylogous Michael Initiated Ring Closure Reaction of 4-Nitroisoxazole Derivatives to 3-Isopropylidene Oxindoles

Herein, we present the first ever use of 3-isopropylidene oxindoles as electrophiles in vinylogous Michael initiated ring closure reaction (MIRC). Among the various alkylidene oxindoles used in enantioselective spirocyclization reactions, isopropylidene oxindoles are the least explored to date. The competing reactivity of isopropylidene oxindoles (electrophilicity vs nucleophilicity) in the presence of a chiral organocatalyst is controlled by the logical selection of a more reactive nucleophile. The methodology produces a library of densely substituted highly enantioenriched spirocyclopropyl oxindoles with excellent yield and stereoselectivities. Moreover, the first enantioselective synthesis of HIV-1 NNRT inhibitor indicates the importance of our synthesized spiro-cyclopropyl oxindole core.

Construction of Unique Spiro[dibenzo[a,f]azulene-6,2'-indenes] via Unprecedented Annulation of ortho-C-H Bond of Benzylidene Group

The domino reaction of alkyl and aryl isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C resulted in unique functionalized spiro[dibenzo[a,f]azulene-6,2'-indenes] in good yields, in which the two 2-arylidene-1,3-indanediones acted as different building blocks to construct the polycyclic system. More importantly, the unprecedented anticipation of the ortho-position of benzylidene group to form a novel dibenzo[a,f]azulene ring through a formal [5 + 2] cycloaddition process was first observed. On the other hand, DABCO-promoted reaction of the isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C afforded functionalized spiro[cyclopenta[a]-indene-2,2'-indene] derivatives.

Convenient construction of polycyclic architectures via multicomponent reaction of amino acids, dialkyl but-2-ynedioates and 2-(o-hydroxyarylidene)-1,3-indanediones

Unique polyheterocyclic compounds were efficiently synthesized by cascade reaction of the in situ generation of a special kind of azomethine ylide, 1,3-dipolar cycloaddition and annulation of phenoxide.

Enantioselective Organocatalytic Three-Component Vinylogous Michael/Aldol Tandem Reaction among 3-Alkylidene oxindoles, Methyleneindolinones, and Aldehydes

We reported a one-pot enantioselective three-component vinylogous Michael/aldol tandem reaction of prochiral 3-alkylidene oxindoles with methyleneindolinones and aldehydes using bifunctional organocatalysts. A variety of enantioenriched 3,3-disubstituted oxindoles 3 and spirolactones 4 were generated in moderate yields (up to 78%) with high stereoselectivities (up to >20:1 dr, >99% ee). Intriguingly, we observed that the aldol reaction with paraformaldehyde generates 3,3-disubstituted oxindoles 3 bearing a hydroxymethyl group, while the reaction with aliphatic aldehydes generates spirolactones 4.

Selective Synthesis of Diverse Spiro-oxindole-fluorene Derivatives via a DABCO-Promoted Annulation Reaction of Bindone and 3-Methyleneoxindoles

A DABCO-promoted annulation reaction of bindone ([1,2'-biindenylidene]-1',3,3'-trione) and 3-methyleneoxindoles showed very interesting molecular diversity under different reaction conditions. The base-promoted annulation reaction of bindone and 3-phenacylideneoxindoles in DCM at room temperature afforded spiro[indeno[1,2-a]fluorene-5,3'-indoline] derivatives in good yields and with high diastereoselectivity. However, the similar reaction of 2-(2-oxoindolin-3-ylidene) acetates resulted in Z/E-isomeric spiro[indeno[1,2-a]fluorene-5,3'-indolines] with diastereomeric ratios of 2:1 to 10:1. On the other hand, the DABCO-promoted annulation reaction of bindone and 3-methyleneoxindoles in acetonitrile at different temperatures selectively gave spiro[benzo[5,6]pentaleno[1,6a-b]naphthalene-7,3'-indoline] derivatives and complex dispiro[indoline-3,6'-[4b,6a]ethanoindeno[1,2-a]fluorene-14',3″-indolines] in satisfactory yields.

Enantioselective Synthesis of Spiropyrazolone-Fused Cyclopenta[c]chromen-4-ones Bearing Five Contiguous Stereocenters via (3+2) Cycloaddition

An enantioselective synthesis of spiropyrazolone-fused cyclopenta[c]chromen-4-ones is demonstrated via a (3+2) cycloaddition reaction. The reactions of 3-homoacylcoumarins and α,β-unsaturated pyrazolones in the presence of the cinchona-alkaloid derived hydrogen-bonding catalyst provide aforementioned spiropyrazolone-chromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 98%) with good to excellent stereoselectivities (>25:1 dr and up to 99% ee). This one-pot methodology could also be practically demonstrated on a gram-scale with similar efficacy.

Chromone–indanedione reactant: a bifunctional 3C synthon for diastereoselective construction of skeleton-diversified bispiro-[chromanocyclopentane-oxindole-indanedione]

A new type of bifunctional 3C synthon, a chromone–indanedione precursor, was employed for diastereoselective Michael/Michael cycloaddition with methyleneindolinones to generate a series of potentially bioactive bispiro-[chromanocyclopentane-oxindole-indanedione] frameworks with skeletal diversity in a single operation.

Stereoselective formal [3 + 3] annulation of 3-alkylidene-2-oxindoles with β,γ-unsaturated α-keto esters

1,4-Diazabicyclo[2.2.2]octane (DABCO)-catalyzed [3 + 3] cycloaddition reaction of 3-alkylidene-2-oxindole and β,γ-unsaturated α-keto esters under mild reaction conditions afforded the spirocyclohexene-oxindole with excellent diastereoselectivity. The [3 + 3] annulation is found to proceed through a vinylogous Michael-aldol cascade reaction and it allows rapid access to a diverse set of highly functionalized spirocyclohexene-oxindoles. Also, a bioactivity study of the compounds on mammalian sarcoma cells has reflected cell growth inhibitory/anti-cancer properties.

Design, synthesis and biological evaluation of indole-2-one derivatives as potent BRD4 inhibitors

Bromodomain protein 4 (BRD4) plays a crucial role in transcriptional regulation and is considered to be a viable drug target for cancer treatment. Herein, we designed and synthesized a series of indole-2-one derivatives through scaffold hopping drug design. Most of the compounds showed potent BRD4 inhibitory activities and anti-proliferation activities in cancer cell lines. Especially, compound 12j exhibited excellent BRD4 inhibitory activities (BD1 IC₅₀ = 19 nM, BD2 IC₅₀ = 28 nM) and anti-proliferation potency with IC₅₀ values of 4.75 μM and 1.35 μM in HT-29 and HL-60 cells, respectively. Additionally, docking studies showed that the hydrophobic pocket next to KAc region and WPF shelf were critical to the activity of the compound. Compound 12j could arrest the cell-cycle progression of HT-29 cells into the G1 phase and reduce the expression of c-Myc. Moreover, compound 12j exhibited favorable oral pharmacokinetic properties. All the results demonstrated that compound 12j was a potent BRD4 inhibitor and had merely potential for colon cancer treatment.

Direct Access to Bridged Tetrahydroquinolines and Chromanes via an InCl3-Catalyzed Sequential Three-Component Cascade

A sequential three-component cascade process was developed for the synthesis of bridged tetrahydroquinolines and chromanes bearing 2,6-methanobenzo[d][1,3]diazocine and 2,6-methanobenzo[g][1,3]oxazocine scaffolds, respectively, in good yields from readily available materials. The InCl₃-catalyzed reaction progressed via enamine formation, Michael addition, intramolecular cyclization, and intramolecular iminium ion cyclization steps. Notably, this high atom economic approach (-2H₂O) allowed the generation of four new bonds (1 C-C and 3 C-N or 1 C-C, 1 C-O and 2 C-N) and two heterocyclic rings in a single operation.

Domino Reaction of Aromatic Aldehydes and 1,3-Indanediones for Construction of Bicyclo[2.2.2]octanes and Dibenzo[b,g]indeno[1',2':3,4]fluoreno[1,2-d]oxonines

Triethylamine promoted the pseudo-five-component reaction of aromatic aldehyde with four molecules of 1,3-indanediones in refluxing ethanol to give unique polycyclic bicyclo[2.2.2]octane derivatives containing bridged- and spiro-indanone scaffolds in good yields. The mechanistic studies supported that the reaction included base-catalyzed cyclotrimerization of 1,3-indanedione to give an active cyclic diene and the sequential Diels-Alder reaction with in situ generated 2-arylidene-1,3-indanediones as electron-deficient dienophiles. On the other hand, the pseudo-four-component reaction of salicylaldehyde with 1,3-indanedione afforded the dibenzo[b,g]indeno[1',2':3,4]fluoreno[1,2-d]oxonines in high yields. This reaction clearly demonstrated the high efficiency, molecular convergence, atom-economy, and impressive selectivity of multicomponent reactions.

Tandem grinding reactions involving aldol condensation and Michael addition in sequence for synthesis of 3,4,5-trisubstituted isoxazoles

A one-pot, base-catalyzed, tandem grinding process involving carrying out aldol condensation and Michael addition in sequence to produce 3,4,5-trisubstituted isoxazoles from 3,5-dimethyl-4-nitroisoxazole, aromatic aldehydes and activated methylene compounds has been developed. In the presence of 10 mol% of pyrrolidine, aldol condensations of 3,5-dimethyl-4-nitroisoxazole with various aromatic aldehydes were performed with 3-10 minutes of grinding to provide 5-styryl-3-methyl-4-nitroisoxazoles in good to quantitative yields without further purification. Then, Michael additions between 5-styryl-3-methyl-4-nitroisoxazoles and activated methylene compounds (including ethyl 2-nitroacetate and alkyl 2-cyanoacetates) were carried out in the presence of 10 mol% of Et3N in the same mortar with 3-5 minutes of continuous grinding to produce 3,4,5-trisubstituted isoxazoles in good to excellent yields.

Construction of Dispiro-Indenone Scaffolds via Domino Cycloaddition Reactions of α,β-Unsaturated Aldimines with 2-Arylidene-1,3-indenediones and 2,2'-(Arylmethylene)bis(1,3-indenediones)

The catalyst-free domino reaction of α,β-unsaturated N-alkyl or N-arylaldimines with two molecules of 2-arylidene-1,3-indanediones in dry acetonitrile resulted in polysubstituted spiro[indene-2,3'-indeno[2',1':5,6]pyrano[2,3-b]pyridines] in moderate to good yields and with high diastereoselectivity. The reaction mechanism included sequential aza/oxa-Diels-Alder reactions via both endo-transition states. On the other hand, the catalyst-free domino reaction of α,β-unsaturated N-arylaldimines with 2,2'-(arylmethylene)bis(1,3-indenediones) afforded the mixed diastereoisomeric dispiro[indene-2,1'-cyclohexane-3',2″-indene] derivatives in satisfactory yields. The reaction mechanism of this formal [3 + 3] cycloaddition was believed to proceed with sequential nucleophilic 1,4-/1,2-additions.

Construction of indeno[1,2-a]fluorene via domino reaction of 1,3-indanedione and 3-arylideneindolin-2-ones or chalcones

The base promoted domino reaction of 1,3-indanedione with 3-arylideneindolin-2-ones or chalcones afforded novel polysubstituted indeno[1,2-a]fluorenes.