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Formation of Cyclobutylidenepyrazolines by Methanolysis of 6‐(2,3,3‐Trifluorocyclobutenyl)‐4,5‐diazaspiro[2.4]hept‐4‐ene

“…Note that the action of NaOMe/MeOH on 3-(2,3,3-trifluorocyclobut-1-enyl)-1-pyrazoline, which was prepared previously [1] by the 1,3-dipolar cycloaddition of diazomethane to vinyltrifluorocyclobutene 3, at Ϫ20°C resulted in the intense resinification of the reaction mixture, and we failed to identify the expected products of the substitution of methoxy groups for fluorine atoms. This result is indicative of a specific effect of a spirocyclopropane unit on the stability of the resulting cyclobutylidenepyrazolines 5, which remain unchanged at 0°C for several months.…”

“…Initially, we found that the action of an excess of NaOMe in MeOH on compound 2 at Ϫ20°C (i.e., under conditions [1] that were used for preparing pyrazoline 2 from olefin 1) did not result in the formation of new products, such as methoxy derivatives, which were detected upon reaction with in situ generated diazocyclopropane on vinyltetrafluorocyclobutane (1; the reaction mixture was monitored by TLC for 2 h). In contrast, the reaction of olefin 1 with an equimolar amount of NaOMe in CD 2 Cl 2 at Ϫ20°C gave vinyltrifluorocyclobutene (3; approx.…”

“…In our case, methoxy derivatives could be formed via either the partial dehydrofluorination of parent olefin 1 into 1-vinyl-2,3,3-trifluorocyclobutene (3) and its conversion into 6-(2,3,3-trifluoro-1-cyclobutenyl)-4,5-diazaspiro [2.4]hept-4-ene (4) by reaction with diazocyclopropane or the direct dehydrofluorination of tetrafluoride 2 into pyrazoline 4, and further methanolysis of the latter. Indeed, we found previously [1] that unsaturated com-pound 3 reacts with diazocyclopropane, generated in situ by the decomposition of N-cyclopropyl-N-nitrosourea upon reaction with a mixture of KOH and K 2 CO 3 .…”

“…Previously [1,2] we reported that the interaction of 3-vinyl-1,1,2,2-tetrafluorocyclobutane (1) with diazocyclopropane, which was generated in situ by the decomposition of Ncyclopropyl-N-nitrosourea upon reaction with NaOMe at Ϫ20°C, afforded a diastereomeric mixture of 6-(1,1,2,2-tetrafluorocyclobutyl)-4,5-diazaspiro [2.4]hept-4-enes (2) as a result of 1,3-dipolar cycloaddition. In this case, minor products (4Ϫ6%) were formed along with the main pyrazolines 2, which were formed with a total yield of 48% (isomer ratio 2.3:1).…”

“…In this case, minor products (4Ϫ6%) were formed along with the main pyrazolines 2, which were formed with a total yield of 48% (isomer ratio 2.3:1). According to preliminary data, [1,2] the structure of these minor products corresponds to the partial formal substitution of methoxy groups for fluorine atoms upon reaction with NaOMe. The nucleophilic substitution of fluorine atoms in fluorinated cyclobutanes has been reported previously;…”