The thermally induced rearrangements of 2-vinyloxirane

Abstract

. Can. J. Chem. 54, 3364 (1976).The kinetics of the gas phase thermoiysis of Zvinyloxirane (4) have been studied over the temperature range 270-310 "C. The racemization of chiral 4 occurs six times faster than the structural ison~erization to 2,3-dihydrofiran, (E)-and (d)-2-butenai, and 3-butenal. The butenals undergo a slow ihermolysis to propene and carbon monoxide. cis-Deuterio-and frnr2s-3-deuterio-vhyioxirai1~ have been synthesized and their interconversion is slow. Deuterium kinetic isotope ezects on motzo-and dideurerio-4 suggest that for the formation of the kutenals the rate determining step involves rupture of the oxirane C-0 bond. The dihydrofuran is produced by thermolysis of the oxirane C-C bond. The preferred mechanistic interpretatiur, is that a carbon-oxygen diradical serves as an intermediate for butenal formation, and that a carbonyi-ylide is involved in the formation of the dihydrofuran.Tile relative rates, at 307.4 " C , of cis-irans-isomerizatim:diI1ydrofuran formation: racemization: butenal formation for 3-dcuterio-2-vinyloxirane are On a CtudiC, B des ten~pCratures ai!ant de 270-310 'C, la cinktique de ia thermolyse en phase gazeuse du vinyl-2 oxiranne (4). La racCrnisation du composk 4 chiral se pioduib 6 fois plus rapidemnt que I'isorn6risation de structure en dihydro-2,3 furanne, en butkne-2 als ( E ) et ( Z ) el en Sutkne-3 al. Les butenais subissent !me therinolybe lente conduisant au propkne et au monoxyde de carbone. On a aussi syntbCtisC les deutCrio-3 vinyloxirannes cis et trans et !cur interconversion est lente. Ees effets isotopiques cinktiques du deuterium sur les motlo-et diderlririo 4 suggkrent que, pour la formation des butknals, I'etape dCtermiriant la vitesse de la rCaction irnplique la rupture du lien C--0 de l'oxiranne. Le dihydrofuranne se produit par thermolyse du lien C-C de i'oxiranne. L9interprCtation mkcanistique prCf6rCe implique qu'il y a formation d'un diradical carbone-oxygkne comnle interinkdiaire pour la formation des butenais et qu'un carbonyl-yfide est irnplique dans la formation de la dihydrofuranne. kes vitesses relatives, B 307.4 "C, pour I'isomCrisation cis-tratzs: la formation de dilvdrohranne: la rackmisation: la formation de butenal B partir du de~lterio-3 vinyl-2 oxiranne sont respectivement de 1.0:0.88 :40.2:5.94.[Traduit par le journal]

Detailed kinetic modeling of 1,3-butadiene oxidation at high temperatures

“…It is known that vinyloxirane undergoes rapid ring expansion to 2,3-dihydrofuran at relatively low temperatures [13,14] [15] to be unimolecular isomerizations to crotonaldehyde and cyclopropanecarboxaldeldehyde.…”

The mechanism of the thermal decarbonylation of 2,2-dimethyl-3-butenal

“…We suggested that the decarbonylation of 3-butenal was both radical catalyzed and under oxygen free conditions proceeding via an intramolecular mechanism. To study this more thoroughly we have examined the thermolysis of the non-enolizable 2,2-dimethyl-3-butenal (1). There are few instances of decarbonylation of P,y-unsaturated aldehydes.…”

Catalytic Ring Expansion Adventures

“…1 Although less relevant to our task, it was also known that vinyl oxiranes can be thermally ring expanded at high temperatures (>350°C) to form oxonium ylide intermediates, which then cyclize to form 2,3-dihydrofuran products. 2 Researchers had shown that catalysts could selectively insert into the allylic C-O vinyl oxirane bond and that the intermediate metallocycle could be used for ring expansions, which, in the examples shown, were used to form β-lactones. 3 The few ring expansion 'solutions' that were reported were low yielding, used substrates that were rigged to avoid the detrimental hydride shift pathway, or relied on an S N 2' type strategy using, in most cases, iodide as a nucleophile.…”

“…6 We deliberately chose a vinyl oxirane substrate to study that was quite sensitive to Lewis acids and, as a result, formation of the unwanted aldehyde side product. Our first successful copper(II) catalyst that significantly favored 2,5-dihydrofuran formation was copper(II)acetylacetonate [Cu(acac) 2 ]. Despite the relatively high temperatures (150°C) and long reaction times (17 h), we were excited about this result.…”

“…We were pleased to learn that Cu(tfacac) 2 not only proceeded to catalyze the reaction in only two hours [eight times faster than Cu(acac) 2 ] but, more importantly, increased the 2,5-dihydrofuran/aldehyde selectivity to a useful 12:1 ratio. Pushing this approach one step further, we evaluated the performance of Cu(hfacac) 2 . This turned out to be the best catalyst for this transformation, affording the desired product in only 15 minutes [70-fold faster and 3-fold more selective than Cu(acac) 2 ] and 86% isolated yield.…”