Tandem Double-Michael-Addition/Cyclization/Acyl Migration of 1,4-Dien-3-ones and Ethyl Isocyanoacetate: Stereoselective Synthesis of Pyrrolizidines

Anion Cascade Reactions II: Synthesis of 3-Isoquinuclidone-Based Bridged Polycyclic Lactams

A facile and convenient anion cascade strategy was developed for the synthesis of bridged-ring amides in moderate to excellent yields in one step in the presence of tBuOK in EtOH under mild conditions, starting from various cheap and commercially available 2-cyanoacetamides and precisely designed straight-chain and annular 1,4-dienones. This simple protocol was generally applicable to a wide range of substrates with high chemical conversion and diastereoselectivity.

Divergent Synthesis of Chromenoindoles and Spiroindolines via Domino Reaction of Indolyl-Substituted Isocyanides with Quinone Esters

A dearomative spirocyclization of tryptamine-derived isocyanides with quinone esters is developed for the divergent synthesis of structurally complex chromeno[2,3-b]indole and polycyclic spiroindoline scaffolds. This domino reaction features the formation and conversion of the six-membered dihydropyran ring with an amendable N,O-aminal moiety.

Diastereodivergent synthesis of chromeno[2,3-b]chromenes by tuning all of the reactivity centers of isocyanoacetate

A novel diastereodivergent tricyclization of isocyanoacetates with o-quinone methides was accomplished for the efficient synthesis of chromeno[2,3-b]chromene derivatives. All three reactive centers of isocyanoacetate reacted sequentially with two o-QMs, affording the products with four adjacent stereocenters in a diastereoselective manner. The asymmetric version was preliminarily investigated.

Silver-promoted dearomative [3+4] cycloaddition of anthranils with α-isocyanoacetates: access to benzodiazepines

The first example of silver-promoted [3+4] cycloaddition of α-isocyanoacetates with anthranils as aromatic Michael accepters, offering access to benzo[d][1,3]diazepinones, has been developed. Mechanistic studies revealed that an "oxygen migration" rearrangement process was involved in this dearomative cycloaddition reaction. Additionally, benzo[d][1,3]diazepinones were obtained efficiently as well under catalytic conditions. Broad functional groups were well tolerated under mild reaction conditions.

Ionic Reactivity of 2-Isocyanoaryl Thioethers: Access to 2-Halo and 2-Aminobenzothia/Selenazoles

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides has been successfully developed for the efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. This synthetic protocol, incorporating a halogen atom when forming the five-membered ring of benzothia/selenazoles, is different from the existing ones, where halogenation of the preformed benzothia/selenazole precursors happens. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.

Recent Advances in the Transition Metal-Free Synthesis of Heterocycles from α, β-Unsaturated Ketones

Heterocyclic compounds are an inevitable part of our life. These important classes of molecules have a wide range of applications starting from life-sustaining drugs to agrochemicals. Numerous methods, including metal...

Dinucleophilic Reactivity of Isocyanoacetate: Base-Catalyzed One-Pot Access to 4-Azafluorenes and 4-Azafluorenones

A base-catalyzed double annulation of isocyanoacetates with various enynones has been developed for the expeditious synthesis of 4-azafluorene and 4-azafluorenone derivatives. Against the well-known 1,3-dipolar reactivities, the active methylene and isocyano groups of isocyanoacetate serve as nucleophiles in this domino transformation.

Cu/base co-catalyzed [3+3] cycloaddition for the synthesis of highly functionalized 4-fluoropyridines

An efficient, straightforward and general method for the de novo synthesis of highly functionalized 4-fluoropyridines was developed via a cooperative copper- and base-catalyzed [3+3] cycloaddition of active methylene isocyanides with difluorocyclopropenes. The resulting 4-fluoropyridines can be readily diversified by various nucleophiles.

Silver-Catalyzed Asymmetric Dearomatization of Electron-Deficient Heteroarenes via Interrupted Barton-Zard Reaction

Herein we report a catalytic asymmetric dearomatization reaction of electron-deficient heteroarenes with α-substituted isocyanoacetates through an interrupted Barton-Zard reaction. A range of optically active pyrrolo[3,4-b]indole derivatives was obtained in good yields (up to 97 %) with high stereoselectivities (up to >20:1 dr and 97 % ee), using a catalytic system consisting of a cinchona-derived amino-phosphine and silver oxide. This reaction features wide substrate scope and mild conditions, and provides a new strategy for developing asymmetric dearomatization reactions.

A catalyst-free aqueous mediated multicomponent reaction of isocyanide: expeditious synthesis of polyfunctionalized cyclo[b]fused mono-, di- and tricarbazoles

A new multi-component reaction is developed for the synthesis of cyclo[b]fused mono-, di- and tricarbazoles from o-alkenyl arylisocyanides, aldehydes, and cyclic diketones in ethanol/water (1 : 1) as the solvent system.

Domino synthesis of fully substituted pyridines by silver-catalyzed chemoselective hetero-dimerization of isocyanides

A silver-catalyzed hetero-dimerization of various vinyl isocyanides with isocyanoacetamides has been developed for the efficient and practical synthesis of fully substituted pyridines in a single operation.

Synthesis of Benzothiophene-Fused Oxa[6.6.5]tricyclic Skeletons through a Cinchonidine- or NaOH-Promoted Quadruple Domino Sequence

Two base-promoted quadruple domino reactions between thioaurones and allylic phosphonium salts have been developed to synthesize benzothiophene-fused oxa[6.6.5]tricyclic skeletons in moderate to good yields with excellent stereoselectivity and broad functional-group tolerance. This is a simple and useful protocol for the rapid construction of the umbrella-like oxa[6.6.5]tricyclic skeleton.

[1 + 2 + 3] Annulation as a General Access to Indolo[3,2- b]carbazoles: Synthesis of Malasseziazole C

A formal [1 + 2 + 3] annulation of methyleneindolinones with o-alkenyl arylisocyanides has been developed for the general and efficient synthesis of both symmetrical and unsymmetrical indolo[3,2- b]carbazoles. The chemoselectivity of this domino reaction was tuned by a tethered alkenyl group, which enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology was used as a key step in the synthesis of the alkaloid malasseziazole C.

A [4 + 1] annulation of ortho-electrophile-substituted para-quinone methides for the synthesis of indanes and isoindolines

Indanes and isoindolines were obtained via a 1,6-conjugated addition/1,4-Michael addition of ortho-electrophile-substituted para-quinone methides with nucleophiles in high yields and with good functional group tolerance.

Formal [1 + 2 + 3] Annulation: Domino Access to Carbazoles and Indolocarbazole Alkaloids

A new formal [1 + 2 + 3] annulation of o-alkenyl arylisocyanides with α, β-unsaturated ketones under metal-, base-, and acid-free conditions is disclosed. This domino reaction provides a general protocol for the efficient and practical synthesis of a wide range of carbazole derivatives from readily available starting materials in a single operation. Furthermore, this methodology was used as the key step in a protecting-group-free synthesis of indolocarbazole alkaloids arcyriaflavin A and racemosin B.

Triple Nucleophilic Attack of Nitromethane on (2-Iminoaryl)divinyl Ketones: A Domino Synthetic Strategy for Hexahydrophenanthridinones

A novel domino reaction of (2-iminoaryl)divinyl ketones with nitromethane was developed for the efficient synthesis of hexahydrophenanthridin-9(5H)-ones. The reaction proceeded smoothly from readily available starting materials under mild reaction conditions to construct three new bonds and two rings with high diastereoselectivities in good to excellent yields in a single step. A mechanism is proposed, involving a stepwise double Michael addition/aza-Henry reaction cascade, and in this transformation, nitromethane acts as a trinucleophile.

Catalytic asymmetric synthesis of pyrrolidine derivatives bearing heteroatom-substituted quaternary stereocenters

An enantioselective [3 + 2] cycloaddition of heteroatom-substituted alkenes with α-substituted isocyanoacetates has been developed. Excellent reactivity and enantioselectivity were obtained.

"In Water": Organocatalyzed Diastereoselective Multicomponent Reactions toward 2-Azapyrrolizidine Alkaloid Scaffolds

Synthesis of the 2-aza analogues of pyrrolizidine and spirooxindole-2-azapyrrolizidine hybrid, a spiro-tetracyclic scaffold possessing multiple contiguous stereocenters, by an exclusive regio-, chemo-, and diastereoselective multicomponent reaction in water is reported. This logical and didactical tactic has integrated the principles of an ideal organic synthesis, privileged substructure-based diversity-oriented synthesis, and biology-oriented synthesis to access hybrid heterocyclic scaffolds.

Silver-catalyzed formal [3+2]-cycloaddition of α-trifluoromethylated methyl isocyanides: a facile stereoselective synthesis of CF3-substituted heterocycles

An Ag-catalyzed formal [3+2]-cycloaddition of α-trifluoromethylated methyl isocyanides with polar double bonds has been developed for the expeditious synthesis of trifluoromethylated oxazolines, imidazolines and pyrrolines under mild conditions.

Organocatalyzed aerobic oxidative Robinson-type annulation of 2-isocyanochalcones: expedient synthesis of phenanthridines

An unprecedented organocatalyzed aerobic oxidative Robinson annulation of 2-isocyanochalcones with active methylene ketones was developed for the expedient synthesis of phenanthridines and hydrophenanthridinones in high to excellent yields.