7086-07-9Relevant articles and documents
Carbonyl ylides and carbenes from thermolysis of oxadiazolines. Substituent effects on intramolecular and intermolecular reactions of carbonyl ylides
Bekhazi, Michel,Warkentin, John
, p. 619 - 624 (2007/10/02)
Thermolysis of a 2-methoxy-Δ3-1,3,4-oxadiazoline involves loss of N2 with formation of carbonyl ylide.The fate of the carbonyl ylide depends on its enviroment and on the other substituents present.Thus, the ylides from 2-methoxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline (1) and from 2-methoxy-2-(4-methoxyphenyl)-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (2) are trapped very efficiently by methanol.However, the ylide from 1 is trapped much less efficiently than that from 2 by dimethylacetylene dicarboxylate, cis-1,2-dichloroethylene, or norbornadiene.A major competitive process in the case of 1 is fragmentation of the ylide to carbonyl compounds and carbenes, the latter being trapped by alkenes to form cyclopropanes.An intramolecular 1,4-H transfer is also competitive under some conditions.The ylide from 2 does not appear to fragment, nor does it undergo the 1,4-H transfer, but it cyclizes efficiently to the oxirane in the absence of trapping agents.Preliminary estimates of rate constants for cyclization of ylide from 2 to form the oxirane (kcycl31 deg C = 1.3*1E-6 s-1) and for its additions to norbornadiene and to dimethylacetylene dicarboxylate (1*1E-5 M-1s-1 and 1*1E-9 M-1s-1, respectively are reported.If it is assumed that the ylide from 1 would add to dimethylacetylene dicarboxylate with a similar rate constant, then the yield for that process can be used to place a lower limit of 1010s-1 on the rate constant for fragmentation of that ylide at 31 deg C.
