In the last few years, the development of versatile methodologies to incorporate trifluoromethyl groups into organic molecules has attracted significant attention in synthetic chemistry. This review gives an overview over the development on the trifluoromethylation of alkynes, which have not been solely discussed before. Formation of diverse C(sp, sp², sp³)CF₃ bonds are all covered in this review.

A copper-catalyzed difunctionalizing trifluoromethylation of activated alkynes with the cheap reagent sodium trifluoromethanesulfinate (NaSO₂CF₃ or Langlois’ reagent) has been developed incorporating a tandem cyclization/dearomatization process. This strategy affords a straightforward route to synthesis of 3-(trifluoromethyl)-spiro[4.5]trienones, and presents an example of difunctionalization of alkynes for simultaneous formation of two carbon–carbon single bonds and one carbon–oxygen double bond.

A convenient strategy is presented for the easy preparation of a series of 2 H-chromenes under mild conditions through iodocyclization of readily accessible propynols. In addition, various 4-chromanones can be synthesized through a p-toluenesulfonic acid catalyzed cascade cyclization with high efficiency (yields up to 99 %). Our developed reaction systems are proven to have good functional-group applicability and can be scaled up to gram quantities in satisfactory yields. These systems also provide a new synthetic strategy for two types of important flavonoid skeleton without using costly and toxic metal catalysts. Additionally, the resulting halides could be further exploited in subsequent palladium-catalyzed coupling reactions, so these compounds could act as potential intermediates for the construction of some valuable drug molecules.

An efficient synthetic approach to tetrahalogenated spiroketals has been developed through a tandem iodocyclization of various α,β-diynyl ketodiols. The diastereoselective construction of a chiral spiroketal center induced by the chiral alkynol functional groups is possible. The obtained tetrahalogenated spiroketals can be applied in subsequent palladium-catalyzed coupling reactions to produce compounds with multiple aromatic substituents.

A convenient zinc-promoted [4+3] cycloaddition of a carbonyl ene–yne with simple dienes was first achieved. This reaction provided an efficient strategy to prepare various cyclohepta[b]furan rings by cascade cycloadditions. Additionally, a multicomponent reaction of dione, alkynal, and diene was also reported, which exhibited a novel strategy for selective creations of CO bonds and CC bonds.

A new and efficient Pd^II-catalyzed intermolecular annulation of N-benzoylsulfonamide with allenes for the synthesis of 3,4-dihydroisoquinolin-1(2H)-ones is reported. This CH functionalization is compatible with ambient air and moisture, and it can be applied to terminal or internal allenes with different synthetically attractive functional groups. Control experiments and a kinetic isotope effect study are conducted and a plausible mechanism is proposed.

A novel copper-catalyzed one-pot functionalization of homopropargylic alcohols that involves trifluoromethylation, aryl migration, and formation of a carbonyl moiety has been developed. This reaction constitutes the first direct conversion of homopropargylic alcohols into CF₃-containing 3-butenal or 3-buten-1-one derivatives in a regioselective manner. Mechanistic studies indicate that the 1,4-aryl migration proceeds through a radical pathway.

A novel and direct synthesis of 1-aryl-5-arylvinyl-tetrazoles from easily prepared propargylic alcohols and TMSN₃ is developed in the presence of TMSCl under mild conditions (TMS=trimethylsilyl). The process involves an allenylazide intermediate, followed by a CC-bond cleavage and CN-bond formation to afford the desired products. Moreover, this method offers a good functional-group applicability and can be scaled-up to grams (yield up to 85 %).

A straightforward method for the synthesis of highly functionalized vinylarenes through palladium-catalyzed, norbornene-mediated CH activation/carbene migratory insertion is described. Extension to a one-pot procedure is also developed. Furthermore, this method can also be used to generate polysubstituted bicyclic molecules. The reaction proceeds under mild conditions to give the products in satisfactory yields using readily available starting materials. This is a Catellani–Lautens reaction that incorporates different types of coupling partners. Additionally, this reaction is the first to demonstrate the possibility of combining Pd-catalyzed insertion of diazo compounds and Pd-catalyzed CH activation.

Without extra addition of sulfinate salt, allylic sulfones were synthesized by palladium-catalyzed cross-coupling of aryl iodide with N-tosylhydrazone. In this transformation, not only the diazo compound but also the sulfinate salt, which were both generated in situ from base-mediated decomposition of the N-tosylhydrazone, was used as nucleophilic partner.

A platinum-catalyzed cascade heterocyclization and formal [3+2] cycloaddition reaction of 2-(1-alkynyl)-3-aryl-2-propenals and arylethenes has been developed. This cyclization reaction shows excellent regioselectivity to obtain highly substituted 4H-cyclopenta[b]furans in moderate to excellent yields.

A gold-catalyzed benzannulation of enynones for synthesizing oxabicyclic compounds and naphthyl ketones with high regioselectivity has been developed. Divergent products can be obtained from the same substrates through different types of cycloaddition. In this reaction, enynones were selectively transformed through [3+2] cycloadditions to give oxabicycles 2 in the presence of [L³AuCl] (L³=[tris(para-trifluoromethylphenyl)phosphine], 5 mol %). When [L²(CNCH₃)Au]SbF₆ (L²=[2-(di-tert-butylphosphino)biphenyl]) was used as the catalyst, the [4+2] cycloaddition naphthyl ketone products dihydrobenzo[f]isoquinolines 3 were obtained. The value of this method is indicated by the applicability of various enynones substrates and the highly regioselective synthesis of two potentially useful polycyclic compounds.

Functionalized 3,4-dihalogenated furan-2(5 H)-ones can be readily prepared in moderate to good yields by treating 4-hydroxy-4-arylbut-2-ynoate derivatives with ICl, IBr, and I₂. Both halogen atoms of the electrophile are incorporated in the product. The resulting halides can further afford polycyclic aromatic compounds using known palladium-catalyzed coupling reactions.

A mild and direct pathway for the formation of five-membered heterocyclic compounds from hydroxylated enynes has been developed. In this reaction, hydroxylated enynes were selectively transformed into five-membered heterocyclic compounds 2, with an allene moiety at the 3-position, in the presence of F₃CSO₃H (0.1 mol %). When R¹, R²=Ph, diphenylvinyl-2,3-dihydro-1H-pyrrole (2 y) was obtained. With HSbF₆ (5 mol %) as the catalyst, polycyclic skeletons 3 and 4 with adjacent stereocenters were obtained. When R¹=H and R²=styrene, 1,3-dienyl-2,5-dihydro-1H-pyrrole (6 as) was formed. This Brønsted acid catalyzed domino process involves the formation of an allene carbocation intermediate, which can be readily trapped by olefins to give various novel five-membered heterocyclic skeletons.

A simple and tandem synthetic approach, which offers an efficient, direct route to highly substituted indenes, has been developed by palladium- or nickel-catalyzed cyclization of propargylic compounds and nitrogen nucleophiles. The reaction takes place under mild conditions, and a possible mechansim is proposed.

An interesting migration of the rigid structure of benzene was observed when propargylic esters were introduced to the cyclization chemistry of o-alkynyl(oxo)benzene. Various 8-oxabicyclo[3.2.1]octane derivatives with many functional groups could be synthesized from this efficient approach catalyzed by platinum. The high stereo- and regioselectivity involved in this transformation was also attractive.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A variety of polysubstituted 3-iodopyrans were readily prepared in good to excellent yield under mild reaction conditions by the reaction of alkynyl carboxamides with ICl, I₂, and NIS. The products obtained from this process are versatile materials that can be used to construct other complex functionalized pyran structures of importance. The occurrence of the pyranyl group in both natural products and pharmaceuticals confers important value to this study. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A simple, convenient and efficient synthetic approach to highly substituted pyrroles has been developed by utilizing a gold(III)-catalyzed tandem amination-intramolecular hydroamination reaction. The first examples of gold-catalyzed, selective amination of 1-en-4-yn-3-ols have also been disclosed.

A simple and convenient synthetic approach to difurylmethane derivatives has been developed via gold-catalyzed cycloisomerization of 1-oxiranyl-2-alkynyl esters and dimerization of the 2-(α-hydroxyalkyl)furans. The reaction takes place in the presence of 2 mol% of tetrachloroauric acid tetrahydrate (HAuCl₄⋅4 H₂O) under very mild conditions.

Highly substituted indene and naphthalene derivatives have been readily prepared in good-to-high yields by a palladium-catalyzed domino reaction. This domino reaction involves a Heck carbopalladation/cyclization/coupling process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A novel gold-catalyzed tandem cyclization/[1,2]-alkyl migration process of epoxy alkynes to spiropyranones has been discovered. From this process, the construction of adjacent multiple stereocenters with a new quaternary carbon atom is achieved. The gold-catalyzed domino process is stereospecific with respect to the migrating carbon atom. A type of unusual CC bond cleavage of epoxide systems has also been discovered, which can lead to the formation of two Z alkenes and a carbonyl functional group in one step with excellent stereoselectivity. Furthermore, this efficient domino process could be achieved in the presence of the simplest and least expensive gold catalyst [NaAuCl₄]⋅2 H₂O with a low catalyst loading.