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We report novel insights into the cascade rearrangement of destabilized vinyl cations deriving from the BF3·Et2O-induced decomposition of cyclic α-diazo-β-hydroxy ketones in turn prepared by aldol-type condensation of cycloalkanones with diazoacetone. Complexation of the hydroxy group of the α-diazo-β-hydroxy compound with the Lewis acid is the first event, followed by the generation of the cycloalkanylidenediazonium salt that, after nitrogen loss, produces the highly reactive vinyl cation. The subsequent ring expansion results in the formation of a cycloalkenyl vinyl cation that affords the allylic cation by 1,2-methylene shift and ring contraction. The cation can then trap the solvent, the fluoride or the hydroxide released from the [BF3OH]− to afford different reaction products. The effect of both solvent and substrate ring size on products types and ratios were analyzed and discussed from a mechanistic point of view.

[Display omitted] • A high-crystal-density 1-trinitromethyl-3,4,5-trinitropyrazole was synthesized for the first time. • The target compound has high oxygen balance (+18.1 %), excellent thermal stability (160 ℃), and high specific impulse (I sp : 243 s), which is a potential energetic oxidiser. • One kind of N -alkylation reagents (diazoacetone) was used in the research field of energetic materials. 3,4,5-Trinitropyrazole was successfully functionalized with the trinitromethyl group to give 1-trinitromethyl-3,4,5-trinitropyrazole (3), which was structurally characterized by IR, NMR, elemental analysis, and single-crystal X-ray diffraction. Compound 3 exhibits a super-high density (2.006 g cm−3 at 170 K, 1.964 g cm−3 at 296 K), excellent oxygen balance (+18.1 %), and good thermal stability (160 ℃). With X-ray data and quantum computing, the intermolecular interactions of 3 was carefully studied to investigate its structure–property relationship. The high density, excellent oxygen balance, good thermal stability, along with its green feature (chloride free) make compound 3 a potential replacement for ammonium perchlorate (AP) and ammonium dinitramide (ADN) in solid propellants. [ABSTRACT FROM AUTHOR]

Diazoacetone reacts with methyl acrylate in the presence of anhydrous GaCl to give isomeric methyl 2-acetylcyclopropanecarboxylates rather than pyrazolines obtained from diazo esters or by noncatalytic reactions. In a similar reaction, diazoacetophenone yields methyl 2-benzoylcyclopropanecarboxylates, benzoylmethyl acrylate, and benzoylmethyl 2-benzoylcyclopropanecarboxylate via partial transesterification. Addition of an equimolar amount of GaCl to diazoacetone in the system CHCl-HCl-HO unexpectedly produces 4,5-dimethylfuran-3(2 H)-one and 1,1′-oxybis(propan-2-one). [ABSTRACT FROM AUTHOR]

Abstract: α-Triethylsilyl-α-diazoacetone underwent a sequential aldolisation–deprotection–aldolisation process to access the 2-diazo-3-oxo-1,5-dihydroxy skeleton with significant diversity. The diazo group could be efficiently removed by treatment with rhodium acetate to afford the corresponding 5-hydroxy-1,3-diketones. [Copyright &y& Elsevier]

We report novel insights into the cascade rearrangement of destabilized vinyl cations deriving from the BF3·Et2O-induced decomposition of cyclic α-diazo-β-hydroxy ketones in turn prepared by aldol-type condensation of cycloalkanones with diazoacetone. Complexation of the hydroxy group of the α-diazo-β-hydroxy compound with the Lewis acid is the first event, followed by the generation of the cycloalkanylidenediazonium salt that, after nitrogen loss, produces the highly reactive vinyl cation. The subsequent ring expansion results in the formation of a cycloalkenyl vinyl cation that affords the allylic cation by 1,2-methylene shift and ring contraction. The cation can then trap the solvent, the fluoride or the hydroxide released from the [BF3OH]− to afford different reaction products. The effect of both solvent and substrate ring size on products types and ratios were analyzed and discussed from a mechanistic point of view. [ABSTRACT FROM AUTHOR]