Functionalization of Acetalic C(sp3)‐H Bonds by Scandium(III) Triflate‐Catalyzed Intramolecular Redox Reactions: Tandem 1,4‐Hydride Transfer/1,5‐Cyclization Processes Leading to Protected 1‐Indanones

A new C C bond forming reaction leading to adjacent quaternary carbons is reported. It is a one‐pot hydride shift/cyclization process facilitated by the hydricity of the acetalic C H bonds, with benzylidenemalonate fragments as electrophilic hydride acceptors, and the catalysis of scandium(III) triflate. The reaction products are 1,2‐dihydroindane derivatives. Alkoxy and alkanethiolate groups can be also intramolecularly transferred from the acetalic carbon to the electrophilic benzylidenemalonate CC bond.     

A General Method for the Synthesis of 5H‐Benzo[b]‐, Carbazolo[2,3‐b]‐ and Indolo[2,3‐b]carbazole Derivatives via Copper(II) Triflate‐Catalyzed Heteroannulation

A straightforward approach for the construction of 5H‐benzo[b]‐, carbazolo[2,3‐b]‐ and indolo[2,3‐b]carbazole derivatives has been developed by using copper(II) triflate‐catalyzed heteroannulation.     

Silver Triflate‐Catalyzed or Electrophile‐Mediated Tandem Reaction of N′‐(2‐Alkynylbenzylidene)hydrazides with Dimethyl Acetylenedicarboxylate

Different outcomes were generated under different conditions for the tandem reactions of N′‐(2‐alkynylbenzylidene)hydrazides with dimethyl acetylenedicarboxylate (DMAD) catalyzed by silver triflate or in the presence of electrophiles. The unexpected isoquinoline‐based azomethine ylides were obtained when the reaction was catalyzed by silver triflate or in the presence of bromine, while the fused 1,2‐dihydroisoquinolines were afforded when iodine was employed in the above tandem reactions.     

Palladium‐Catalyzed Tandem Reaction of Alkyne‐Based Aryl Iodides and Salicyl N‐Tosylhydrazones to Construct the Spiro[benzofuran‐3,2′‐chromene] Skeleton

A convenient palladium‐catalyzed tandem reaction of aryl iodides and salicyl N‐tosylhydrazones has been achieved to afford a series of compounds containing the novel spiro[benzofuran‐3,2′‐chromene] scaffold in moderate to good yields. This efficient catalytic reaction, which tolerates various functional groups, combines alkyne‐based 5‐exo‐dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization, generating three new bonds in one reaction.

     

An Efficient Route to 3‐Amidylindoles via a Palladium‐ Catalyzed Tandem Reaction of 2‐Alkynylanilines with Isocyanides

A palladium‐catalyzed reaction of 2‐alkynylaniline, isocyanides, and silver acetate is described, leading to 3‐amidylindoles in moderate to good yields. During the process, five new bonds are formed with high reaction efficiency in one‐pot procedure.     

Gold‐Catalyzed Redox Synthesis of Imidazo[1,2‐a]pyridines using Pyridine N‐Oxide and Alkynes

A mild, catalytic, atom economical synthesis of imidazo[1,2‐a]pyridines has been developed: catalytic dichloro(2‐pyridinecarboxylato)gold [PicAuCl₂] in the presence of an acid produces a range of imidazo[1,2‐a]pyridines in good yields starting from alkynes and 2‐aminopyridine N‐oxides. This strategy is mild and foreseen to be of particular use for the installation of stereogenic centers adjacent to the imidazo[1,2‐a]pyridine ring without loss of enantiomeric excess.

     

Generation of 11‐Fluoro‐11H‐indeno[1,2‐c]quinolines via a Palladium‐Catalyzed Three‐Component Reaction of 2‐Alkynylbromobenzenes, 2‐Alkynylanilines,and N‐Fluorobenzenesulfonimide

A novel and efficient synthesis of 11‐fluoro‐11H‐indeno[1,2‐c]quinolines has been developed via a palladium‐catalyzed three‐component reaction of 2‐alkynylbromobenzenes, 2‐alkynylanilines, and N‐fluorobenzenesulfonimide. The reaction works well with high selectivity. Additionally, the diversity and complexity could be easily introduced via a simple operation from readily available starting materials. In the meantime, a fluorine atom could be incorporated into the scaffold during the reaction process.     

Gold‐Catalyzed Synthesis of 3‐Acylimidazo[1,2‐a]pyridines via Carbene Oxidation

A convenient gold‐catalyzed strategy for the synthesis of imidazo[1,2‐a]pyridine derivatives has been developed via gold carbene complexes. This transformation opens a new synthetic route to a variety of 3‐carbonyl‐substituted imidazo[1,2‐a]pyridines using air as oxidant affording the products in good yields.

     

Regioselective Synthesis of 1,2‐ and 1,4‐Dihydroquinolines by Palladium‐Catalyzed Intramolecular N‐Arylation

A series of 1,2‐ and 1,4‐dihydroquinolines has been successfully prepared. The Pd‐catalyzed intramolecular N‐arylation of Z‐enamines, formally prepared by the Horner–Wadsworth–Emmons olefination, proceeded efficiently to furnish the cyclized products. Depending on the cyclization conditions, substituted 1,4‐dihydroquinolines and further isomerized 1,2‐dihydroquinolines were independently obtained in high yields with an excellent control of isomerization of the double bond.

     

Gold(I)‐Catalyzed Cascade for Synthesis of Pyrrolo[1,2‐a:2′,1′‐c]‐/Pyrido[2,1‐c]pyrrolo[1,2‐a]quinoxalinones

An efficient and convenient method was developed for the one‐pot construction of the complex polycyclic heterocycles pyrrolo[1,2‐a:2′,1′‐c]‐/pyrido[2,1‐c]pyrrolo[1,2‐a]quinoxalinones from two simple starting materials via a gold(I)‐catalyzed domino reaction. This strategy presents an atom economical and environmentally friendly transformation, in which two new C N bonds and one new C C bond are formed in a one‐pot reaction process.     

Brønsted Acid‐Catalyzed Four‐Component Cascade Reaction: Facile Synthesis of Hexahydroimidazo[1,2‐a]pyridines

An efficient four‐component cascade reaction for the synthesis of trisubstituted hexahydroimidazo[1,2‐a]pyridines starting from readily available aldehydes, ketones and ethane‐1,2‐diamine catalyzed by p‐toluenesulfonic acid is described. Two new cycles and five new bonds are constructed with all reactants being efficiently utilized in this transformation. The mechanism of the reaction was investigated and some crucial reaction intermediates were observed.     

Diversified Construction of Chromeno[3,4‐c]pyridin‐5‐one and Benzo[c]chromen‐6‐one Derivatives by Domino Reaction of 4‐Alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes

Silver‐catalyzed three‐component, tandem reactions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes, amines and various nucleophiles result in the formation of highly functionalized chromeno[3,4‐c]pyridin‐5‐ones in high yields. Gold‐catalyzed [4+2] cycloadditions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes with alkynes or alkenes have also been achieved to afford benzo[c]chromen‐6‐ones efficiently.

     

Proline‐Mediated Enantioselective Construction of Tetrahydropyridines via a Cascade Mannich‐Type/Intramolecular Cyclization Reaction

A highly diastereo‐ and enantioselective synthesis of 2,3‐disubstituted tetrahydropyridines was accomplished via a proline‐mediated cascade Mannich‐type/intramolecular cyclization reaction from preformed N‐PMP (p‐methoxyphenyl) aldimines and inexpensive aqueous tetrahydro‐2H‐pyran‐2,6‐diol.     

Palladium‐Catalyzed Intramolecular Annulation of 3‐[2‐(2‐Iodobenzylamino)aryl]‐N‐arylpropiolamides: Synthesis of 3‐[5H‐Dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones

A novel palladium‐catalyzed intramolecular tandem annulation method is presented for the synthesis of 3‐[5H‐dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones. This method allows the conversion of various 3‐[2‐(2‐iodobenzylamino)aryl]‐N‐arylpropiolamides to the corresponding 3‐[5H‐dibenzo[b,e]azepin‐11(6H)‐ylidene]indolin‐2‐ones through the diarylation of an alkyne.     

Assembly of Indeno[1,2‐c]chromenes via a Palladium‐Catalyzed Reaction of 1‐Bromo‐2‐(cyclopropylidenemethyl)benzene with 2‐Alkynylphenol

1‐Bromo‐2‐(cyclopropylidenemethyl)benzenes react with 2‐alkynylphenols under palladium catalysis, leading to indeno[1,2‐c]chromenes in moderate to good yields. The molecular complexity and diversity can be introduced efficiently from easily available starting materials.

     

Brønsted Acid‐Catalyzed [3+2] Cyclodimerization of 3‐Alkyl‐ 2‐vinylindoles Leading to the Diastereoselective Construction of a Pyrroloindole Framework

A Brønsted acid‐catalyzed [3+2] cyclodimerization of 3‐alkyl‐2‐vinylindoles has been established, which led to the diastereoselective construction of pyrroloindole frameworks in high yields (up to 98% yield, all >95:5 dr). This reaction not only represents the first application of 3‐alkyl‐2‐vinylindoles as nitrogen‐carbon‐carbon (NCC) building blocks, but also reveals a new [3+2] cyclodimerization of 2‐vinylindoles. Control experiments demonstrated that both the free N H group and the C‐3 alkyl group in the indole moiety play a crucial role in performing the [3+2] cyclodimerization. A preliminary attempt also demonstrated the feasibility of performing heterodimerization.

     

Formal [3+2] Annulation Involving Allylic Bromides and Thioureas. Synthesis of 2‐Iminothiazolidines through a Base‐Catalyzed Intramolecular anti‐Michael Addition

A simple and efficient protocol was developed for the synthesis of 2‐iminothiazolidines through a base‐mediated [3+2] annulation involving substituted thioureas and allylic bromides bearing electron‐withdrawing groups. This domino process consists of nucleophilic displacement, followed by intramolecular anti‐Michael addition of the preformed allylic isothiourea under mild conditions to give the thiazolidine core.

     

Regioselective Copper‐Catalyzed Oxidative Cross‐Coupling of Imidazo[1,2‐a]pyridines with Methyl Ketones: An Efficient Route for Synthesis of 1,2‐Diketones

An efficient copper‐catalyzed oxidative coupling of imidazo[1,2‐a]pyridines with methyl ketones to directly generate structurally sophisticated 1,2‐dicarbonyl imidazo[1,2‐a]pyridine derivatives under oxidative conditions is described. The reaction proceeds in good yields using the environmental friendly molecular oxygen as the oxidant. ¹⁸O‐Labelling experiments unambiguously established that the oxygen of the dicarbonyl products originated from oxygen rather than from water.

     

Synthesis of Pyrazolo[1,2‐a]cinnolines via a Rhodium‐Catalyzed Oxidative Coupling Approach

An efficient synthetic strategy for the unique class of pyrazolo[1,2‐a]cinnolines was developed through a rhodium‐catalyzed oxidative coupling of N‐aryl‐1H‐pyrazol‐5(4H)‐ones with internal alkynes. This protocol features use of the pyrazolone function in the substrate as an intrinsic directing group, hexafluoroisopropyl alcohol (HFIP) as the solvent, and mild reaction conditions as well as a wide substrate scope.