Reactions of 2H-azirines with carbenoids from diazo esters:: transformations of novel azirinium ylides

Thermocatalytic decomposition of diazo esters in the presence of 3-aryl-2H-azirines gives rise to azirinium ylides. The latter preferentially transform via isomerization into 2-azabuta-13-diene derivatives or, with excess diazo compound, via reaction with the Rh-carbenoid to form 3,4-dihydro-2H-pyrrole derivatives. In contrast, ylides generated front 2-monosubstituted or 2,2-disubstituted 3-phenyl-2H-azirines transform exclusively via isomerization into the corresponding 2-azabuta-1,3-dienes in high yields. (C) 2004 Published by Elsevier Ltd.