Copper difluorocarbene-involved catalytic gem-difluoropropargylation

The use of metal for catalytic difluorocarbene transfer reactions has long been hindered by the lack of understanding of metal difluorocarbene chemistry, despite the potential implications for medicinal chemistry and advanced materials science. Here, we report a copper-catalyzed difluorocarbene transfer reaction via 1,1-migration of copper difluorocarbene, in contrast to the previous nucleophilic addition of copper difluorocarbene pathway. This reaction enables the development of a modular catalytic gem-difluoropropargylation reaction using a variety of simple and widely available potassium propiolates, terminal alkynes, and allyl/propargyl electrophiles to couple difluorocarbene, opening an avenue to the precise synthesis of organofluorine compounds without tedious synthetic procedures. The impact of this protocol is demonstrated by the efficient synthesis of complex fluorinated skeletons and the rapid synthesis of key intermediates for pheromone derivatives and PGF2 agonists. Mechanistic studies reveal that the migratory insertion of difluorocarbene into the C-Cu bond of the alkynylcopper species is a key step in the reaction.

Recent advances in the applications of gem-difluoromethylene alkynes

As a special class of alkynes, gem-difluoromethylene alkynes exhibit a variety of fascinating properties due to the presence of the gem-difluoro substitution. This substitution highlights the distinctive fluorine effects in influencing the chemoselectivity of reactions. As a result, chemical scientists have shown great interest and enthusiasm for investigating their reactions. In this review, we briefly summarize recent advances in transition metal-catalysed reactions of gem-difluoromethylene alkynes with multiple reaction pathways. Their mechanistic studies and challenges will be highlighted. The purpose of this review is to provide illustrations of elegant gem-difluoromethylene alkynes and thereby elicit further interest among synthetic chemists in developing innovative transformations of gem-difluoromethylene alkynes.

Rhodium(III)-Catalyzed Annulation Synthesis of Difluorinated Quinazolinone Derivatives Using an Amide Carbonyl as the Directing Group

The use of amide carbonyl groups of substrates as weakly coordinating directing groups has received a significant amount of attention. Recently, difluoromethylene alkynes have been successfully used in fluorination reactions, resulting in the preparation of various fluorine-containing compounds. This work describes a [4+2] annulation method for creating a range of fluorinated quinolino[2,1-b]quinazolinone derivatives. The derivatives are formed through Rh(III)-catalyzed cascade cyclization of 3-phenylquinazolinones and gem-difluoromethylene alkynes.

Solvent-Dependent Selective Synthesis of CF3-Tethered Indazole Derivatives Based on Multiple Bond Activations

Presented herein is a solvent-dependent selective synthesis of CF₃-tethered indazole derivatives via the cascade reactions of 1-arylpyrazolidinones with trifluoromethyl ynones. Mechanistically, the formation of the title products involves cascade N-H/C-H/C-N/C-C bond cleavage along with pyrazole ring formation and pyrazolidinone ring opening. For the formation of a pyrazole scaffold, 1-phenylpyrazolidinone acts as a C2N2 synthon, while trifluoromethyl ynone serves as a C1 synthon. Meanwhile, trifluoromethyl ynone also acts as an enol unit to facilitate the ring opening of the pyrazolidinone ring and provide a trifluoropropenoxy fragment via cleavage of the alkynyl triple bond and migration of the cleaved moiety. When the reaction was run in trifluoroethanol instead of DCE, it selectively afforded indazole derivatives tethered with a trifluoroethoxy moiety through in situ transesterification. To our knowledge, this is the first synthesis of CF₃-tethered indazole derivatives via concurrent alkynyl activation, pyrazole formation, and CF₃ migration.

Regioselective Dichotomy in Ru(II)-Catalyzed C-H Annulation of Aryl Pyrazolidinones with 1,3-Diynes

Herein, we present a substrate-controlled regiodivergent strategy for the selective synthesis of C3 or C2-alkynylated indoles via ruthenium-catalyzed [3 + 2]-annulation of readily available pyrazolidinones and 1,3-diynes. Remarkably, C3-alkynylated indoles were obtained in good yields when 1,4-diarylbuta-1,3-diynes were employed as the coupling partners. On the other hand, dialkyl-1,3-diynes led to the selective formation of C2-alkynylated indoles. The key features of the strategy are the operationally simple conditions and external-oxidant-free, broad-scope, and substrate-switchable indole synthesis. Scale-up reactions and further transformations expanded the synthetic utility of the protocol.

Rh(iii)-catalyzed simultaneous [3 + 3]/[5 + 1] annulation of 1-arylpyrazolidinones with gem-difluorocyclopropenes leading to fluorinated pyridopyrimidinone derivatives

Presented herein is an efficient and concise synthesis of fluorinated pyridopyrimidinone derivatives through formal [3 + 3]/[5 + 1] annulation of 1-arylpyrazolidinones with gem-difluorocyclopropenes.