Organocatalytic Asymmetric Synthesis of C-N Atropisomers with Pyrrole, Oxindole and Succinimide Scaffold

An asymmetric synthesis of C-N atropisomers with pyrrole, oxindole and succinimide moities was developed via organocatalytic desymmetric Michael addition of 3-pyrrolyloxindole with prochiral N-aryl maleimides. The C-N atropisomers were obtained in acceptable yields with high diastero- and enantioselectivities (>20 : 1 dr, up to >99 % ee). C-N Rotational energy barrier has also been determined.

Synthesis of Benzofuro[3,2-b]indol-3-one Derivatives via Dearomative (3 + 2) Cycloaddition of 2-Nitrobenzofurans and para-Quinamines

An efficient dearomative (3 + 2) cycloaddition of para-quinamines and 2-nitrobenzofurans has been developed. This reaction proceeds smoothly under mild conditions and affords a series of benzofuro[3,2-b]indol-3-one derivatives in good to excellent yields (up to 98%) with perfect diastereoselectivities (all cases > 20:1 dr). The scale-up synthesis and versatile derivatizations demonstrate the potential synthetic application of the protocol. A plausible reaction mechanism is also proposed to account for the observed reaction process. This work represents the first instance of the N-triggered dearomative (3 + 2) cycloaddition of 2-nitrobenzofurans.

Sequential organo and metal catalyzed reaction between 3-pyrrolyloxindoles and linear nitroenynes: access to cyclic aza-spirooxindoles

An asymmetric Michael addition/hydroarylation reaction sequence, catalyzed by a sequential catalytic system consisting of a squaramide and a combination of silver and gold salts, provides a new series of cyclic aza-spirooxindole derivatives in excellent yields (up to 94%) and high diastero- and enantioselectivities (up to 7 : 1 dr, up to >99% ee). Computational study has also been performed.

Diastereoselective Synthesis of Dihydrobenzofuran-Fused Spiroindolizidines via Double-Dearomative [3 + 2] Cycloadditions

Spiroindolizidine oxindoles represent a kind of privileged scaffold in many biologically active natural alkaloids. 2,3-Dihydrobenzofuran derivatives exhibit significant bioactivities in a variety of pharmaceuticals. Herein, we assembled these two privileged fragments into a small molecule via double-dearomative [3 + 2] cycloadditions with pyridinium ylides and 2-nitrobenzofurans. This protocol features remarkable advantages including wide substrate scope, mild condition, high level of diastereoselectivities and yields. Thus, a collection of spiroindolizidine-fused dihydrobenzofurans/indolines were facilely produced efficiently.

Dearomative Michael addition involving enals and 2-nitrobenzofurans realized under NHC-catalysis

In this manuscript, the first enantioselective dearomative Michael addition between α,β-unsaturated aldehydes and 2-nitrobenzofurans realized under N-heterocyclic carbene activation has been described. The reaction proceeds via addition of homoenolate to Michael acceptors leading to the formation of biologically important heterocycles with high yields and stereoselectivities. Their functionalization potential has been confirmed in selected, diastereoselective transformations.

Dearomatization of 3-Nitroindoles Enabled Using Palladium-Catalyzed Decarboxylative [4 + 2] Cycloaddition of 2-Alkylidenetrimethylene Carbonates

A dearomatization process of 3-nitroindoles enabled using palladium-catalyzed decarboxylative [4 + 2] cycloaddition of either 2-alkylidenetrimethylene carbonates or 2-(hydroxymethyl)-3-arylallyl carbonates has been developed, affording a wide range of indoline-fused tetrahydropyrans in good yields with excellent diastereoselectivities. This reaction features a wide substrate scope and mild conditions and represents the first example of the application of π-allyl palladium 1,4-[O,C]-dipole species for the dearomative cycloaddition of electron-deficient heteroarenes.

Ag-Catalyzed Asymmetric Interrupted Barton-Zard Reaction Enabling the Enantioselective Dearomatization of 2- and 3-Nitroindoles

We disclose a Ag-catalyzed asymmetric interrupted Barton-Zard reaction of α-aryl-substituted isocyanoacetates with 2- and 3-nitroindoles, which enables the dearomatization of nitroindoles and hence offers rapid access to an array of optically active tetrahydropyrrolo[3,4-b]indole derivatives bearing three contiguous stereogenic centers, including two tetrasubstituted chiral carbon atoms with pretty outcomes (up to 99% yield, 91:9 dr, and 96% ee). The synthetic potential of the protocol was showcased by the gram-scale reaction and versatile transformations of the product.

Asymmetric Decarboxylative [3+2] Cycloaddition for the Diastereo- and Enantioselective Synthesis of Spiro[2.4]heptanes via Cyclopropanation

Asymmetric cycloaddition reaction has emerged as one of the powful and reliable strategies for the construction of enantioenriched molecules, especially those with polycyclic frameworks. Herein, we report the asymmetric decarboxylative...

Higher-order [10 + 2] cycloaddition of 2-alkylidene-1-indanones enables the dearomatization of 3-nitroindoles: access to polycyclic cyclopenta[b]indoline derivatives

The higher-order [10 + 2] cycloaddition of 3-nitroindoles and 2-alkylidene-1-indanones enables the dearomatization of 3-nitroindoles and affords a range of structurally diverse cyclopenta[b]indolines with excellent results.

DBU-catalyzed dearomative annulation of 2-pyridylacetates with α,β-unsaturated pyrazolamides for the synthesis of multisubstituted 2,3-dihydro-4H-quinolizin-4-ones

DBU-catalyzed dearomative [3 + 3] annulation of 2-pyridylacetates and α,β-unsaturated pyrazolamides for the synthesis of multisubstituted 2,3-dihydro-4H-quinolizin-4-ones was developed.

Catalytic Asymmetric Dearomative 1,3-Dipolar Cycloaddition of 2-Nitrobenzothiophenes and Isatin-Derived Azomethine Ylides

An enantioselective dearomative 1,3-dipolar cycloaddition of 2-nitrobenzothiophenes and isatin-derived azomethine ylides with a bifunctional hydrogen-bonding thiourea catalyst was established, giving polyheterocyclic compounds in excellent results (up to 99% yield, >20:1 dr for all cases and up to 99% ee). The enantioselectivity could be reversed by the bifunctional hydrogen-bonding squaramide catalyst containing the same chiral source as in the thiourea catalyst. DFT calculations revealed the origin of the observed stereochemistry and the reversal of enantioselectivity.

Dinuclear Zinc Catalyzed Enantioselective Dearomatization [3+2] Annulation of 2-Nitrobenzofurans and 2-Nitrobenzothiophenes

The application of dinuclear zinc catalysts in a dearomatization reaction has been developed. Catalytic asymmetric dearomatization [3+2] annulations of 2-nitrobenzofurans or 2-nitrobenzothiophenes with CF₃ -containing N-unprotected isatin-derived azomethine ylides catalyzed by dinuclear zinc catalysts are realized with excellent diastereomer ratios (dr) of >20 : 1 and enantiomeric excess (ee) of up to 99 %. This protocol provides a practical, straightforward access to structurally diverse pyrrolidinyl spirooxindoles containing a 2,3-fused-dihydrobenzofuran (or dihydrobenzothiphene) moiety, and four contiguous stereocenters. Reactions can be performed on a gram scale. The absolute configuration of products is confirmed by X-ray single crystal structure analysis, and a possible mechanism is proposed.

Organocatalytic Asymmetric Synthesis of Aza-Spirooxindoles via Michael/Friedel-Crafts Cascade Reaction of 1,3-Nitroenynes and 3-Pyrrolyloxindoles

An asymmetric [3+3] cyclization of nitroenynes and 3-pyrrolyloxindoles has been realized with a chiral bifunctional squaramide catalyst. This Michael/Friedel-Crafts cascade strategy provides a facile and efficient access to enantioenriched polycyclic aza-spirooxindoles with 32-95% isolated yields and excellent stereocontrol under mild reaction conditions.

Dearomative 1,6-addition of P(O)–H to in situ formed p-QM-like ion pairs from 2-benzofuryl-ols to C3-phosphinoyl hydrobenzofurans

We report a dearomative C3-phosphorylation and a tandem C3-phosphorylation/aromatization of 2-benzofuryl-ols with P(O)–H species to afford C3-phosphinoyl hydrobenzofurans and benzofurans, respectively.

Catalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones: stereoselective construction of dihydrobenzofuran-bridged polycyclic skeletons

An organocatalytic asymmetric dearomative [4 + 2] annulation of 2-nitrobenzofurans and 5H-thiazol-4-ones is developed for the construction of dihydrobenzofuran-bridged polycyclic skeletons with good results.

Palladium-catalyzed asymmetric allylic alkylation of 3-aminooxindoles to access chiral homoallylic aminooxindoles

An organometal catalytic conversion of 3-aminooxindoles for the diastereo- and enantioselective synthesis of homoallylic aminooxindoles has been described. The asymmetric allylic alkylation of 3-aminooxindoles with allyl carboxylates proceeded smoothly to afford a series of chiral 3-allyl-3-aminooxindoles. This work offers an alternative route to build these scaffolds. The application of this protocol is also highlighted by a significant conversion of products to the potential applicable spiro[indoline-3,2'-pyrrolidin]-2-one derivatives.

Copper-Catalyzed Decarboxylative [3 + 2] Annulation of Ethynylethylene Carbonates with Azlactones: Access to γ-Butyrolactones Bearing Two Vicinal Quaternary Carbon Centers

An efficient decarboxylative [3 + 2] annulation reaction of ethynylethylene carbonates and azlactones has been developed with a copper salt as catalyst. This practical methodology gives access to a diverse library of γ-butyrolactones bearing α,β-two vicinal quaternary carbon centers in good to high yields with good levels of diastereoselectivities (up to 98% yield, >95:5 dr). Preliminary trials on enantioselective variant with a chiral PyBox ligand provided chiral products in up to 71% ee. This synthetic method features mild reaction conditions, broad functional group tolerance, large-scale synthesis, and versatile products transformation. A plausible catalytic cycle for the protocol is proposed based on previous related studies and our experimental observations.

Organocatalytic asymmetric tandem α-functionalization/1,3-proton shift reaction of benzylidene succinimides with β-trifluoromethyl enones

A bifunctional thiourea-catalyzed asymmetric tandem α-functionalization/1,3-proton shift reaction of benzylidene succinimides with β-trifluoromethyl enones has been developed. A series of F₃C-containing chiral Rauhut-Currier type products were obtained in moderate to high yields (up to 98%) with excellent enantioselectivities (up to >99% ee). This represents the first example of benzylidene succinimides undergoing tandem α-functionalization/1,3-proton shift in catalytic enantioselective transformation.

[4 + 2] Annulation Reaction of In Situ Generated Azoalkenes with Azlactones: Access to 4,5-Dihydropyridazin-3(2H)-Ones

An unprecedented [4 + 2] annulation reaction between in situ formed azoalkenes and azlactones has been developed. This reaction provides a facile access to an array of 4,5-dihydropyridazin-3(2H)-one derivatives, which are very promising in medicinal applications as potential biologically active candidates. Notably, these dihydropyridazinones could also be synthesized via a one-pot reaction protocol by using the in situ formed azlactones from N-acyl amino acids and in situ generated azoalkenes from α-halogeno hydrazones. The potential applications of the methodology were also demonstrated by gram-scale experiments and the versatile conversions of the products into other nitrogen-containing compounds.