Synthesis and Thermal Stability of O-Vinylketoximes

Abstract

The O-vinylketoximes 2 were synthesized from ketoximes 1 and acetylene in superbase systems in good to excellent yields. Their thermal stability was investigated.O-Vinylketoximes, precursors in the synthesis of pyrroles from ketoximes and acetylenes, 1 contain a highly reactive NO-vinyl group and attract much attention as promising monomers and synthons. However, they are potentially explosive and hence for their safe and proper application in organic synthesis and polymer chemistry, the knowledge of their thermal stability is crucial. Meanwhile, no data of such a kind were so far published.Direct acetylene vinylation of a ketoxime, namely acetoxime 1a, was first reported 20 years ago. 2 The reaction was carried out under atmospheric pressure at 110°C, the yield of O-vinylacetoxime being 10%. Later, the yield was improved up to 78% by carrying out the reaction in an autoclave (80-90°C, initial acetylene pressure 15 atmospheres) and by use of fractional vinylation. 3 However, this procedure turned out to be poorly reproducible.A series of vinylketoximes 2 was unselectively prepared by using superbase systems MOH-DMSO (M = Li, Na, K) under acetylene pressure, 3-12 with the help of indirect methods using halogen derivatives. 13,14 The synthetic conditions and yields of 2 are presented in Table 1.The goal of the present work was to develop high-performance and reliable synthetic routes to O-vinylketoximes of accessible alkyl-and arylmethylketones and to undertake their stability investigation.Using vinylation of acetoxime 1a (R 1 = Me, R 2 = R 3 = H) as a model, the effect of the reaction parameters on the yield and purity of O-vinylketoximes under both atmospheric and elevated pressure has been examined. The results of acetoxime vinylation under atmospheric pressure are presented in Table 2. The runs were carried out in a flow system; the O-vinylacetoxime 2a formed was brought out with the acetylene flow into a trap cooled to -78°C. The formation of undesirable (in this case) pyrroles 3 and 4 during O-vinylacetoxime synthesis 1 was suppressed by water additives. 2,3 At the same time, it is known that the presence of water in the alkali-DMSO system decreases its basicity 15 and, consequently, the ketoxime-acetylene reaction rate. Indeed, variation of the reaction conditions has shown the yields of O-vinylacetoxime 2a to increase with decreasing the concentration of water and increasing the amount of alkali loading (Table 2). A significant growth (from 30% to 42%) of the yield of 2a with increasing the amount of alkali (Table 2, runs 3-5) or with reducing the acetoxime concentration (Table 2, run 6) is observed under anhydrous conditions. The synthesis of oxime 2a under the conditions of runs 3-5 may be considered as a preparative one, but, though experimentally simple, it suffers from shortcomings. First, a considerable portion of the initial acetoxime transforms to the pyrroles 3a and 4a. Second, a loss of O-vinylacetoxime 2a is observed owing to its high volatility in the presence of acetylene; in the trap a sol...

Superbase‐catalyzed domino 3H‐pyrroles synthesis from ketoximes and acetylene: DFT study vs experiment

“…The synthesis of pyrroles from ketoximes and acetylene (Trofimov reaction) is considered as a domino reaction starting from the formation of O ‐vinylketoximes B , which undergo 3,3‐sigmatropic shift to iminoaldehydes D further cyclizing to 5‐hydroxypyrrolines E and giving final products G after a water molecule elimination (Scheme ). This mechanism has been repeatedly confirmed by observation and isolation of main intermediates ( O ‐vinylketoximes B , N , O ‐dialkenylhydroxylamines C and iminoaldehydes D ,), but rarely studied computationally …”

1,2-Dioximes in the trofimov reaction

“…16 The thermally initiated (~150°C) spontaneous and in some cases explosive decomposition of compounds containing an O-vinyloxime group was observed earlier in the case of O-vinylketoximes [19] and O-vinylamidoximes [20]. The total yield of the O-vinylation products 14 and 15 and the relative content of the divinyl derivative 15 are doubled if the reaction temperature in the potassium hydroxide-DMSO system is increased from 60 to 80°C.…”

Dioximes of 1,3-Diketones in the Trofimov Reaction: New 3-Substituted Pyrroles

“…enabled the isolation for the first time of a mixture of the corresponding O-vinyloximes containing an α-methylene group [20], which was not possible up to the present time on vinylation of alkyl-, aryl-, and 2-hetaryl ketoximes [19,21]. …”