Ring expansions of N-methyl-1,2,5-oxadiazolium and 1,2,3-triazolium perchlorate salts with bases to six-membered azines: direct detection of an addition intermediate in an addition–elimination mechanism and a degradation of 1,2,5-oxadiazolium salts to α-cyano nitrones

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Richard N. Butler, Elaine C. McKenna, John M. McMahon, Karen M. Daly, Desmond Cunningham and Patrick McArdle


Abstract

Reactions of 2-methyl-1,2,5-oxadiazolium perchlorate salts and 1-methyl-2-aryl-1,2,3-triazolium perchlorate salts with the bases KCN, NaOEt, KOBut, LiNPri2 give ring expansions to substituted 1,2,5-oxadiazines and 1,2,4-triazines. With cyanide as base the reactions follow an addition–elimination pathway and in two cases the addition intermediate has been isolated or directly detected by low-temperature NMR spectroscopy. The oxadiazolium system with cyanide also gives a useful new route to α-cyano nitrones via a ring degradation which competes with ring expansion. The reactions with KOBut and LiNPri2 do not involve an addition of the base to the azolium salt. Reactions have been monitored by 13C NMR spectroscopy by using 13CN. An X-ray crystal structure is reported for (E)-N-(α-cyanobenzylidene)methylamine N-oxide.


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