Regio- and Diastereoselective Hydrophosphination and Hydroamidation of gem-Difluorocyclopropenes

In this study, concise, efficient, and modular hydrophosphinylation and hydroamidation of gem-difluorocyclopropenes were disclosed in a mild and transition-metal-free pattern. Through this approach, phosphorus, and nitrogen-containing gem-difluorocyclopropanes were produced in moderate to good yields with excellent regio- and diastereoselectivity. Readily available gem-difluorocyclopropenes and nucleophilic reagents, along with inexpensive inorganic bases, were employed. Multiple synthetic applications, including gram-scale and derivatization reactions and modification of bioactive molecules, were subsequently elaborated.

CsF-Mediated Reaction of Trifluorodiazoethane with 3-Nitroindoles Enables Access to Trifluoromethylpyrazolo[4,3-b]indoles

A mild and metal-free strategy for the construction of trifluoromethylated pyrazolo[4,3-b]indoles through the reaction of N-substituted 3-nitroindoles with trifluorodiazoethane is reported. This operationally simple transformation involves a [3 + 2] cycloaddition of trifluorodiazoethane with 3-nitroindole, followed by the elimination of the nitro group to furnish pyrazole-fused indoles. The synthetic utility of this method is further demonstrated by applying it to other heterocycles, such as 3-nitrobenzothiophene and 2-nitrobenzofuran.

Construction of heterocyclic rings from cyclopropenes

Heterocyclic rings are the fundamental building blocks of biological systems and have wide applications in synthetic chemistry and medicinal science. The development of novel synthetic methodology for heterocyclic skeletons from a variety of starting materials has made great progress in the past decades. Meanwhile, highly strained cyclopropenes as reactive reagents in organic transformations have drawn much attention from chemists. The rich chemical reactivity and reaction routes have been well investigated, and some review articles related to the reactivity of cyclopropenes and the construction of carbocycles and acyclic compounds have appeared in these years. Thus, this review mainly focuses on the progress in the construction of heterocyclic rings starting from various cyclopropenes including the reactions of commonly available stable cyclopropenes, in situ generated reactive cyclopropenes and cyclopropene precursors during this decade. Firstly, the transformations of common cyclopropenes into donor-type vinyl metal carbenes via transition metal induced ring opening, direct metalation of the CC bond of metal complexes, and cycloaddition reactions with 1,3-dipoles are described. Next, the annulation reactions of reactive cyclopropenes generated in situ with donor-acceptor reagents, intramolecular nucleophilic addition, and the cycloaddition reactions with 1,3-dipoles are introduced. Then, the transformation of cyclopropene precursors such as alkyl 1-chloro- or 1-alkoxy-2-aroylcyclopropanecarboxylates into five-membered heteroaromatic compounds is also mentioned. In addition, a brief outlook of the opportunity and challenges in the field of bio-orthogonal reactions related to cyclopropenes is given.

Synthesis of 4-trifluoromethyl pyridazines via annulation of pyridinium ylides with trifluoroacetyl diazoester

A base promoted annulation of pyridinium ylides with trifluoroacetyl diazoester has been reported. Highly functionalized 4-trifluoromethyl pyridazines were synthesized in good yields without the use of any heavy metal catalysts. The developed methodology was compatible with a variety of important functional groups. Mechanistic studies revealed that trifluoroacetylated hydrazone was an active intermediate of this three-component annulation. Synthetic versatility of the method via aminolysis and condensation toward amide- and pyridazino[4,5-c]pyridazine-derivatives has been showcased.

Zinc-Enabled Annulation of Trifluorodiazoethane with 2H-Azirines to Construct Trifluoromethyl Pyrazolines, Pyrazoles, and Pyridazines

A diethylzinc-promoted unconventional annulation reaction of 2,2,2-trifluorodiazoethane with 2H-azirines is described. This transformation involves two [3 + 2] cycloaddition steps and one dinitrogen extrusion process in one pot, thus giving a broad array of 3-trifluoromethyl pyrazolines in good yields with excellent diastereoselectivities. Further transformations provide facile access to 3-trifluoromethyl pyrazoles and 3,5-ditrifluoromethyl pyridazines with good efficiency.

Synthesis of pertrifluoromethyl pyridazine derivatives via a tandem reaction of aryldiazonium salts with hexafluoroacetylacetone

A method for the synthesis of pertrifluoromethyl pyridazine derivatives by the condensation of arenediazonium salts with hexafluoroacetylacetone has been developed.

A rhodium-catalyzed three-component reaction of arylisocyanides, trifluorodiazoethane, and activated methylene isocyanides or azomethine ylides: an efficient synthesis of trifluoroethyl-substituted imidazoles

A novel method for the synthesis of trifluoroethyl-substituted imidazoles is reported via a rhodium-catalyzed three-component reaction of isocyanides, 2,2,2-trifluorodiazoethane and activated methylene isocyanides or azomethine ylides.

Highly enantioselective synthesis of trifluoromethyl cyclopropanes by using Ru(ii)–Pheox catalysts

An asymmetric synthesis of various trifluoromethyl cyclopropanes from olefins, such as vinyl ferrocene, vinyl ethers, vinyl amines, vinyl carbamates and dienes, was achieved by using Ru(ii)–Pheox catalysts.

Heptafluoroisopropyl diazomethane (i-C3F7CHN2): in situ generation and synthesis of pyrazoles

A novel chemical reagent, heptafluoroisopropyl diazomethane (i-C₃F₇CHN₂), has been generated in situ in aqueous media. It reacts with electron-deficient alkynes towards polyfluorinated pyrazoles that are important in agrochemistry.