. Can. J. Chem. 55,3951 (1977).The thermal decarbonylation of 2,2-dimethyl-3-butenal is shown to be an intramolecular extrusion of carbon monoxide concerted with the transfer of hydrogen (deuterium) to the y-position. The reaction displays a kinetic isotope effect of 2.8 (at 296.9"C) and follows first order kinetics (E, = 44.2 L-0.2 kcal mol-l, log A = 13.4 k 0.3).ROBERT J. CRAWFORD, STUART LUTENER et HIROKAZU TOKUNAGA. Can. J. Chem. 55,3951 (1977).On dkmontre que la dkcarbonylation thermique du dimkthyl-2,2 buttne-3 a1 est une extrusion intramoltculaire de monoxyde de carbone concertke avec un transfert d'hydrogkne (deutkrium) vers la position y. La rtaction prtsente un effet isotopique cinttique de 2.8 (a 296.9"C) et suit une cinktique du premier ordre (E, = 44.2 + 0.2 kcal mol-', log A = 13.4 + 0.3).[Traduit par le journal] IntroductionRecently we examined the thermolysis of 2-vinyloxirane (1) and concluded that one of the initial products was 3-butenal which, depending upon the surface of the vessel, was tautomerized to E-or 2-2-butenal or produced propylene and carbon monoxide. Traces of oxygen brought about a catalytic reaction and large amounts of CO and propylene were produced, but even after the most careful conditioning propylene and CO were present. 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. The most thoroughly studied is the work of Schaffner (2) where the singlet photosensitized decarbonylation of R-(+)-laurolenal (2) to S-(-)-1,2,3-trimethylcyclopentene (3) is observed.

. 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]

Die Thermolyse der Titelverbindung (und deuterierter Derivate) bei 300°C ergibt CO und 2‐Methyl‐buten‐(2).