Cycloisomerization between Aryl Enol Ether and Silylalkynes under Ruthenium Hydride Catalysis: Synthesis of 2,3-Disubstituted Benzofurans

Tandem Sulfonylative Annulation/Halogenation of 1,7-Enynes with Sodium Sulfinate and TBAX for the Assembly of 4-Methylenechromanes

An effective and stereoselective synthesis of halogenated (E)-4-methylenechromanes with a sulfonyl group was developed via the copper-catalyzed sulfonylative annulation/halogenation of 1,7-enynes, in which sodium sulfinates were used as the sulfonyl reagents and tetrabutylammonium halide provided the halogen sources. The formed alkenyl C-X bonds were valuable and can efficiently undergo the subsequent hydrolysis, alkenylation, alkynylation, arylation, alkylthiolation, and alkoxylation to furnish a series of highly functionalized 4-methylenechromanes.

Lewis Base-Catalyzed Intramolecular Vinylogous Aldol Reaction and Chemoselective Syntheses of 3-Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines

A Lewis base-catalyzed intramolecular vinylogous aldol reaction of o-(allyloxy)phenyl ketoesters or o-(allylamino)phenyl ketoesters has been developed. This reaction provides ready access to 3-hydroxy-2,3-disubstituted dihydrobenzofurans and indolines in high yields with excellent chemoselectivity and diastereoselectivity. An acid-promoted dehydration of such products further extends the utility of the reaction to the synthesis of 2-alkenyl benzofurans and indoles.

Visible-Light-Mediated Tandem Difluoromethylation/Cyclization of Alkenyl Aldehydes toward CF2H-Substituted Chroman-4-one Derivatives

An efficient and facile visible-light-mediated tandem difluoromethylation/cyclization of alkenyl aldehydes, with easily accessible and air-stable [Ph₃PCF₂H]⁺Br^- as the difluoromethylation reagent, has been established. A range of CF₂H-substituted chroman-4-one skeletons and their derivatives, such as 2,3-dihydroquinolin-4(1H)-ones, chroman, 3,4-dihydronaphthalen-1(2H)-one, 2,3-dihydrobenzofuran, and 2,3-dihydro-1H-inden-1-one, are efficiently produced in moderate to good yields with excellent chemoselectivity under mild reaction conditions.

Intermolecular Sonogashira Coupling and Intramolecular 5-Exo-dig Cycloisomerization Cascade: A One-Pot Pathway for Accessing (3-Benzylbenzofuran-2-yl)(phenyl)methanones

Herein, we present an efficient and straightforward strategy enabling access to 2,3-disubstituted benzo[b]furans. The whole synthetic process proceeds via a domino intermolecular Sonogashira coupling of 2-(2-bromophenoxy)-1-phenylethan-1-ones/alkyl 2-(2-bromophenoxy)acetates/2-(2-bromophenoxy)acetonitrile/1-(2-bromophenoxy)propan-2-one with terminal acetylenes followed by an intramolecular carbanion-yne cyclization in a 5-exo-dig manner and subsequent double-bond isomerization. Notably, two C-C bonds have been constructed in a one-pot manner and a wide variety of (3-benzylbenzofuran-2-yl)(phenyl)methanones were accomplished with good functional group tolerance.

Iron(ii)-induced cycloisomerization of alkynes via"non-vinylidene" pathways for iron(ii)-indolizine and -indolizinone complexes

Reactions between pyridine-functionalized alkynes and an Fe(ii) precursor supported by 2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane afforded the first Fe(ii)-indolizine and -indolizinone complexes. Structural analysis and theoretical calculations revealed the existence of unconventional "non-vinylidene" pathways and challenged the generality of vinylidene intermediacy in Fe(ii)-induced alkyne transformations.

Iridium-Catalyzed Intramolecular Cycloisomerization between Functionalized Alkyne with Aryl Vinyl Ether: Synthesis of 2-Vinyl-3-functionalized Methylbenzofurans

We have developed cycloisomerization between an aryl vinyl ether and a functionalized alkyne, such as silylalkyne, to give 2,3-disubstituted benzofuran derivatives using [IrCl(cod)]₂, PCy₃, and NaBAr^F₄. This catalyst system not only catalyzes the above cycloisomerization but also isomerize a terminal olefin to give an aryl vinyl ether.

Synthesis of 2-Substituted Benzo[b]furans/furo-Pyridines Catalyzed by NiCl2

The first Ni-catalyzed tandem synthesis of 2-substituted benzo[b]furans/furo-pyridines from 2-halophenols and 1-alkynes was explored under Cu-free and phosphine-free conditions. The protocol was carried out with NiCl2/5-nitro-1, 10-phenanthroline in DMA (N,N-dimethylacetamide) at 120 °C. It was found to be simple, cost effective, and have a wide substrate scope. Additionally, the method is compatible with heteroaryl substrates, resulting in the formation of 2-substituted benzo[b]furans/furo-pyridines in reasonable to good yields.

One-Pot Allylation-Intramolecular Vinylogous Michael Addition-Isomerization Cascade of o-Hydroxycinnamates and Congeners: Synthesis of Substituted Benzofuran Derivatives

A unique intramolecular vinylogous Michael addition leading to the synthesis of heterocycles has been disclosed. Base-promoted one-pot sequential O-allylation of o-hydroxy-cinnamates or -cinnamonitrile or -chalcones with γ-bromocrotonates followed by an intramolecular conjugate addition of vinylogous Michael donors resulted in the formation of highly substituted benzofuran derivatives in good to excellent yields. The intramolecular event followed by two [1,3]-H shifts leading to aromatization appears to be the key to the success of this unprecedented transformation.

Platinum-catalyzed selective N-allylation of 2,3-disubstituted indoles with allylic acetates in water

Herein, we have demonstrated that the platinum-catalyzed selective N-allylation of 2,3-disubstituted indoles proceeds in water.

Ruthenium-Catalyzed Intramolecular Double Hydroalkoxylation of Internal Alkynes

Intramolecular double hydroalkoxylation of internal alkynes could be achieved using a Grubbs-type ruthenium carbene complex or its modified species to deliver a series of bridged- and spiroacetal derivatives in moderate to good yields. This study represents a new example of nonmetathetic reactions catalyzed by Grubbs-type ruthenium carbene complexes.

Transition-Metal-Free Cyclization of Propargylic Alcohols with Aryne: Synthesis of 3-Benzofuranyl-2-oxindole and 3-Spirooxindole Benzofuran Derivatives ⊥

An unprecedented base-mediated cyclization of propargylic alcohols with aryne is reported, providing a novel method for the synthesis of 3-benzofuranyl-2-oxindole and 3-spirooxindole benzofuran scaffolds via a propargyl Claisen rearrangement/cycloaddition pathway. The nature of the substituent on acetylene group of propargylic alcohol influences the outcome of the reaction. The protocol offers a transition-metal-free and operationally simple methodology with broad substrate scope as a ready access to complex oxindole-linked heterocyclic compounds.