Regioselective Cycloaddition of Trifluorodiazoethane with Electron-Deficient Allenic Esters and Ketones: Access to CF₃-Substituted Pyrazolines and Pyrazoles

Abstract

A highly regioselective cycloaddition procedure of electron-deficient allenes with trifluorodiazoethane (CF3CHN2) is described. In absence of bases, the reaction proceeded smoothly to give 5-(trifluoromethyl)pyrazolines, whereas the utility of Et3N led to the formation of 3-(trifluoromethyl)pyrazoles.

Telescoping Reactions with Trifluorodiazoethane‐Derived Aza‐Wittig Reagents and Allenyl esters

“…[1][2][3][4][5][6][7] Under Lewis base catalysis, the sp-hybridized b carbon of allenyl estersr eacts with a phosphine or an amine nucleophile to produce zwitterionic intermediates that feature ac arbanion localizeda tt he a or g carbon atoms, the reactivity of whichs trongly depends on the electrophilic partner and reactionc onditions. [9][10][11][12] We thought it would be effective, but we weres urprised to obtain at otally different reaction product, which was identified as an iminophosphorane (Scheme 1b). Great advances have been madew ith the allenyl ester chemical scaffold, which continues to be ab reeding ground for the discoveryo fn ew reactions.…”

“…[8] We envisioned that thesen ovel phosphazenes would react with allenyle sters in af ormal [3+ +2] cycloaddition to provide new trifluoromethylated 3H-pyrazoles, with unprecedented patterns,a nd further aromatic 1H-pyrazoles throught hermal [1,5]-sigmatropic rearrangement( Scheme 1a). [9][10][11][12] We thought it would be effective, but we weres urprised to obtain at otally different reaction product, which was identified as an iminophosphorane (Scheme 1b). We are not aware of any reports on the formation of a-iminophosphorane products from allenyl esters.…”

“…For the purpose of generating molecular diversity from allenyl esters, we oriented our research to uncover new reaction products with phosphazenes (aza‐Wittig reagents) derived from trifluorodiazoethane (CF 3 CHN 2 ) . We envisioned that these novel phosphazenes would react with allenyl esters in a formal [3+2] cycloaddition to provide new trifluoromethylated 3 H ‐pyrazoles, with unprecedented patterns, and further aromatic 1 H ‐pyrazoles through thermal [1,5]‐sigmatropic rearrangement (Scheme a) . We thought it would be effective, but we were surprised to obtain a totally different reaction product, which was identified as an iminophosphorane (Scheme b).…”

A density functional theory study of the stereoselectivity of Cu(OTf)2‐catalyzed [3+2] cycloaddition of trifluoromethylated N‐acylhydrazones and isoprene: A concerted asynchronous mechanism

“…[ 29–32 ] However, investigations concerning the synthesis of CF 3 ‐substituted pyrazolidines and pyrazolines are rather limited. [ 33–39 ] Therefore, methods that can synthesize CF 3 ‐substituted pyrazolidines and pyrazolines efficiently have been widely explored owing to their potential applications in the fields of biology and materials.…”

Syntheses, Experimental and Theoretical Studies on Absorption/Emission Properties of Pyrazoline-Containing Aryl/Methoxynaphthyl Substituents

“…[9][10][11][12][13][14] Substituents of different nature, electron withdrawing group (EWG) and electron releasing group (ERG), in aromatic aldehydes, ketones and hydrazines, make them versatile synthetic auxiliaries in classical organic synthesis. Reports in the literature [15][16][17][18] have attributed an increase in the biological properties of pyrazoline derivatives to the combined effect of ERG, aryl substituents and π-extended configuration. These electronic and structural characteristics of compounds containing the pyrazole nucleus are also widely used in electroluminescence fields.…”