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Alkynes as unsaturated hydrocarbons have long been used for cyclization reactions. Various transition metal-catalyzed cyclizations of alkynes have been reported in the past decades. In this minireview, we mainly summarize the recent asymmetric cyclization of alkynes with other functional groups such as carbonyl-alkynes, cyano-alkynes, and enynes under the catalytic system of nickel and chiral ligands. [ABSTRACT FROM AUTHOR]

A novel palladium-catalyzed oxidative cyclization of aniline-tethered alkylidenecyclopropanes using molecular oxygen as the terminal oxidant through β-carbon elimination of aminopalladation intermediates is disclosed. The reaction opens up an effective way to obtain a series of 2- and 3-vinylindoles which are important synthetic intermediates in many natural indole derivatives. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed divergent synthesis of spirooxindoles fused with a five- or a six-membered ring by a cycloaddition reaction of vinylidenecyclopropane-diesters with methyleneindolinones was disclosed. This protocol features an in situ generated unprecedented zwitterionic π-propargyl palladium species in cycloaddition reactions and a switchable process between (3+2) and (4+2) cycloadditions by changing the phosphine ligand. [ABSTRACT FROM AUTHOR]

A novel gold(i)-catalyzed intramolecular tandem cyclization reaction of ortho-(arylethynyl)arenemethylenecyclopropanes provided an efficient approach to prepare functionalized 11H-benzo[a]fluorene derivatives in moderate to good yields. Further transformations as well as applications of the products have been presented and a plausible reaction mechanism has also been proposed on the basis of deuterium labeling and control experiments. [ABSTRACT FROM AUTHOR]

Copper-catalyzed cascade cyclization of 1,5-enynes with two types of hypervalent reagents was developed via consecutive trifluoromethylazidation/diazidation and intramolecular click reaction (CUAAC), providing one-pot self-assembly of triazole fused isoindolines bearing a trifluoromethyl or an azide moiety. Moreover, the construction of a trifluoromethylcyclopropyl unit, which has been considered as a metabolically stable replacement for a tert-butyl moiety and was difficult to access, was also achieved under trifluoromethylazidation conditions. All these reactions exhibited excellent chemoselectivity, good to excellent yields and broad functional group tolerance. [ABSTRACT FROM AUTHOR]

Novel intramolecular cycloisomerizations of nitrogen-tethered cyclopropenes with indole in the presence of Brønsted acids have been developed. The reactions proceeded through the same pathway but stopped at different stages according to different substituent styles, affording azocino[5,4-b]indole 2 and (epiminoethano)cyclopenta[b]indole 4 in moderate to good yields. [ABSTRACT FROM AUTHOR]

The synthesis of medium-sized heterocycles possessing a trans double bond is still a challenge. Herein, gold(i)-catalyzed 1,2-acyloxy migration/intramolecular cyclopropanation/ring enlargement cascade reaction of furans has been developed, providing highly efficient access to ten- and eleven-membered heterocycles with a broad substrate scope under mild reaction conditions. The reaction outcome features high chemoselectivity at the C5-position of furan. Moreover, a trans-double bond was embodied in the medium ring system. [ABSTRACT FROM AUTHOR]

A ring-opening/cyclization cascade reaction of α-brominated amide-tethered alkylidenecyclopropanes in the presence of photocatalyst 4CzIPN under visible-light irradiation was developed to afford polycyclic benzazepine derivatives in good yields with broad substrate scope and good functional tolerance. A plausible mechanism involving a halogen atom transfer (XAT) process and a radical chain process is proposed for this reaction. This study provides a concise and practical strategy for the synthesis of benzazepine derivatives. [ABSTRACT FROM AUTHOR]

A Pt(ii)-catalyzed cyclization of (hetero)aryl-allenes has been developed, providing controllable synthesis of substituted 2,3-dihydropyrroles and polyheterocyclic skeletons. Another notable feature of this method is the dual-role of the Pt(ii) catalyst: initiation of the migration of the (hetero)arylmethylene group and the subsequent Friedel–Crafts type annulation. [ABSTRACT FROM AUTHOR]

An effective synthetic protocol for structurally diverse 4-acyloxy-1,2-dihydroquinoline compounds has been accomplished by a gold(i)-catalyzed tandem [3,3]-rearrangement and intramolecular hydroamination of propargylic esters, affording the desired products in good yields. Moreover, the asymmetric variant of this cyclization has also been achieved using a chiral nitrogen acyclic carbene (NAC) gold(i) complex. These products have application in the enantioselective synthesis of an aromatase inhibitor within three simple steps. [ABSTRACT FROM AUTHOR]

The unprecedented palladium-catalyzed cascade cyclization of allylamine-tethered alkylidenecyclopropanes with an ethyl difluoroiodoacetate or perfluoroalkylated reagent is developed, providing facile access to a variety of synthetically and medicinally valuable iodine/difluoromethylene- and perfluoroalkyl-containing 1-benzazepine frameworks. These reactions exhibited good yields and functional group tolerance via a radical mechanism. [ABSTRACT FROM AUTHOR]

We have developed a facile synthetic method to access furoquinoline and thienoquinoline derivatives via a thermally induced ring-opening and cyclization reaction from ortho-aminoaryl-tethered alkylidenecyclopropanes with the in situ generation of isocyanates or isothiocyanates. These reactions exhibited excellent yields and functional group tolerance under metal-free conditions. [ABSTRACT FROM AUTHOR]

A facile synthetic method to access 3-substituted isoquinoline or dihydroisoquinoline derivatives has been developed via a novel cyclization reaction of N-sulfonyl-1,2,3-triazole derivatives by thermally induced rearrangement. [ABSTRACT FROM AUTHOR]

The chemoselective [4+2] vs. [2+2] cycloaddition between allenoates and dithioesters can be controlled by switching the nucleophilic amine catalyst. The two modes of cyclizations represent the first example of controllable and chemoselective annulations between allenoates and dienophiles catalyzed by amine. These cyclizations are useful in offering a divergent synthesis of sulfur-containing heterocycles. On the basis of this investigation, it can be realized that dithioesters with a vicinal electron-withdrawing group can react not only like a Michael acceptor but also as a ketone or imine. [ABSTRACT FROM AUTHOR]

A novel phosphine-catalyzed highly diastereoselective [3+2] cycloaddition of isatin derived α,β-unsaturated ketones with α-allenic ester has been developed. [ABSTRACT FROM AUTHOR]