CuCl/Et3N-Catalyzed Synthesis of Indanone-Fused 2-Methylene Pyrrolidines from Enynals and Propargylamines

Dihydro-10H-indeno[1,2-b]benzofurans and Tetrahydroindeno[1,2-c]isochromenes via Stereoselective Intramolecular Carbocation Cascade Cyclization

Nazarov cyclization of the (E)-(2-stilbenyl)methanols under the catalysis of p-TsOH immobilized on silica (PTS-Si) proceeded to give the corresponding indanyl cation with the exclusive trans relationship at the two newly formed adjacent stereogenic centers. The ensuing intramolecular nucleophilic addition by the MOM-protected phenol (m = 0) or benzyl alcohol (m = 1) furnished the Indane-fused benzofuran [5/5] or isochroman [5/6] system, respectively, with the exclusive cis stereocontrol at the two-carbon ring junction. Thus, in a single step, from nonchiral starting materials, the intramolecular cascade carbocation cyclization (CCC) furnished the [5/5] or [5/6] oxygen-containing Indane fused-ring systems in moderate to good yields with excellent stereoselectivity on all three contiguous stereogenic centers.

Palladium-Catalyzed Synthesis of Indanone via C-H Annulation Reaction of Aldehydes with Norbornenes

A novel methodology for the synthesis of indanone derivates has been developed. The palladium-catalyzed annulation reaction of o-bromobenzaldehydes with norbornene derivatives is achieved through extremely concise reaction processes. The indanone skeleton was established directly via C-H activation of the aldehyde group under a mild reaction condition. This method is simple and practical, which simplified the traditional synthesis method for the rapid construction of indanone.

Divergent access to 5,6,7-perifused cycles

Nitrogen-containing heterocycles are the key components in many pharmaceuticals and functional materials. In this study, we report a transition metal-catalyzed high-order reaction sequence for synthesizing a structurally unique N-center 5,6,7-perifused cycle (NCPC). The key characteristics include the formation of a seven-membered ring by the 8π electrocyclization of various alkenes and aromatic heterocycles as π-components, in which metal carbene species are generated that further induce the cleavage of the α-C-H or -C-C bond. Specifically, the latter can react with various nucleophilic reagents containing -O, -S, -N, and -C. The stereo-controlled late-stage modification of some complicated pharmaceuticals indicates the versatility of this protocol.

A regioselective [3 + 2] cycloaddition reaction of 2-benzylidene-1-indenones with functional olefins to access indanone-fused 2D/3D skeletons

The regioselective [3 + 2] cycloaddition reaction of 2-benzylidene-1-indenones with functional olefins was established with DABCO as a base under mild conditions. Using this approach, a series of diversely substituted indanone-fused cyclopentane polycycles with highly crowded multiple substituents were synthesized in high yields.

Intramolecular cyclization reactions of arylpropargyl amides of electron-deficient α,β-alkenyl carboxylates and related compounds

Intramolecular cyclization reactions of arylpropargyl amides of electron-deficient α,β-alkenyl carboxylates such as fumarates and ethenetricarboxylates were investigated. The reaction of the fumaramides with a base, Et₃N or DBU in xylenes at 140 °C under air gave benz[f]isoindoline derivatives in 21-63% yields. The benz[f]isoindolines may be produced via the formation of an allenic intermediate, intramolecular Diels-Alder reaction, proton transfer, and dehydrogenation by oxygen. The suitable bases and the product yields depend on the substituents on the benzene ring. On the other hand, the reaction of the amides of fumarate and ethenetricarboxylate by heating in DMSO gave aroyl-substituted pyrrolidine derivatives as major products, probably via addition of water under metal-free conditions. Furthermore, cyclization reactions of H and Me substituted alkyne derivatives were investigated for comparison. The selective formation of various types of products, such as ethyl 2-(1-benzyl-4-formyl-2-oxopyrrolidin-3-yl)acetate and diethyl 2-(1-benzyl-2-oxo-4-vinylidenepyrrolidin-3-yl)malonate, was found, depending upon the alkyne substituents and the reaction conditions. The reaction mechanisms have been discussed using density functional theory (DFT) calculations.

Cleavage and Reassembly of the C═O Bond of 2-Alkynylbenzaldehydes: A Metal-Free Access to Inden-1-ones

A metal-free approach to inden-1-ones from 2-alkynylbenzaldehydes mediated by pyrrolidine has been developed. The reaction proceeds under mild conditions in a step- and atom-economy process by cleaving the C═O bond and constructing new C-C as well as C═O bonds. Oxygen-18 and deuterium labeling experiments revealed an aza-Petasis-Ferrier rearrangement of an intermediate 1-amino-3-methylene-dihydroisobenzofuran.

A facile and metal-free domino reaction of TsDAM and 2-alkenylarylaldehyde: An easy access to 8-hydroxy-2,8-dihydro indeno [2,1-c]pyrazoles

An efficient straightforward metal free domino approach was developed for the synthesis of various 8-hydroxy-2,8-dihydroindeno[2,1-c]pyrazoles via [3 + 2] cycloaddition of substituted alkenes and TsDAM (TosylDiAzoMethane). The salient features of this protocol include high efficiency, mild reaction conditions, greener solvent, metal-free reaction, scalability and broad substrate scope along with high regioselectivity and yields.

Transition-metal-free oxidative cyclization reaction of enynals to access pyrane-2-one derivatives

A novel and efficient metal-free C-H functionalization of enynals is developed to synthesize α-pyrone derivatives via the formation of two C-O bonds. In this project, K₂S₂O₈ has been introduced as an efficient oxygen source and C-H functionalization agent in regioselective oxidative cyclization reaction with a relatively broad substrate scope.

Recent advances in transition-metal-catalyzed annulations for the construction of a 1-indanone core

Transition metal-catalyzed carbon–carbon bond forming reactions are a well accepted strategy for the synthesis of organic compounds. This review gives a brief update on the transition-metal-catalyzed annulations to construct 1-indanone scaffolds.

Controllable Site-Selective Construction of 4- and 5-Hydroxyalkyl-Substituted Imidazoles from Amidines, Ynals, and Water

The first example of controllable site-selective pathways to construct 4- and 5-hydroxyalkyl-substituted imidazoles through a three-component reaction of amidines, ynals, and water has been documented. Particularly, the high regioselectivity of the reaction was simply switched by changing the additives. In addition, further ¹⁸O-labeled experiments to probe a plausible mechanism and the gram-scale synthesis were studied.

Cu(I)-Catalyzed Three-Component Cyclization for the Construction of Functionalized Thiazoles

A novel and straightforward strategy for the synthesis of functionalized thiazoles from thioamides, ynals, and alcohols via a copper(I)-catalyzed three-component reaction has been described. Through the formation of new C-S, C-N, and C-O bonds in one pot, it is easy to produce various valuable thiazoles fixed with aryl or heteroaryl groups. In addition, the reaction also exhibits other unique advantages, such as high step economics, good functional group tolerance, and good regioselectivity.

Brønsted-acid-catalyzed one-pot tandem annulation/[5 + 2]-cycloaddition of o-propargyl alcohol benzaldehydes with alkynes: regioselective and stereoselective synthesis of dibenzo[a,f]azulen-12-ones

The one-pot synthesis of dibenzo[a,f]azulen-12-ones has been established starting from o-propargyl alcohol benzaldehydes and alkynes.

Synthesis of the Core Structure of Daphnimacropodines

Daphniphyllum alkaloids daphnimacropodines A-C possess a highly congested ring system and share a common tetracyclic ring skeleton. To access the challenging chemical structure of daphnimacropodines, a divergent synthetic approach toward their total synthesis is described. A stereoselective synthesis of the core structure of daphnimacropodines has been achieved from a simple diketone building block. Our approach features an intramolecular carbamate aza-Michael addition and a hydropyrrole synthesis via a Au-catalyzed alkyne hydration followed by an aldol condensation, whereas all the other attempts failed.

Synthesis of 4-(1H-isochromen-1-yl)isoquinolines through the silver-catalysed homodimerization of ortho-alkynylarylaldehydes and subsequent condensation of the 1,5-dicarbonyl motif with NH3

4-(1H-Isochromen-1-yl)isoquinoline derivatives were synthesized in high yields via the AgBF₄-catalyzed self-reaction of ortho-alkynylarylaldehydes to give isochromene intermediates, followed by the dehydration of the 1,5-dicarbonyl motif with NH₃. Compared with electron-rich aromatic substituents, this strategy can provide the desired isochromene products with an electron-deficient isoquinoline unit. The reactions feature simple experimental operations, mild reaction conditions and high product yields.

We demonstrate a strategy that can provide isochromenes with an electron-deficient isoquinoline unit. The reactions feature simple operations, mild conditions and high yields.

Donor- and acceptor-enynals/enynones

Three kinds of transformations based on benzo-fused donor- and acceptor-enynals/enynones, including reactions with alkenes, alkynes, and H₂O, were discussed.

Selectivity-switchable construction of benzo-fused polycyclic compounds through a gold-catalyzed reaction of enyne-lactone

A gold-catalyzed selectivity-switchable reaction of enyne-lactone is reported. The choice of the gold complex is the key for the chemoselectivity.