3-Oxidopyraziniums
are azomethine ylides derived from 2(1H)-pyrazinones
that can undergo 1,3-dipolar cycloadditions
with acrylate and acrylic acid derivatives. The cycloaddition of 1-(4-methoxybenzyl)-5,6-dimethyl-3-oxidopyrazinium
with methyl and tert-butyl acrylate and with methyl
crotonate afforded a 3,8-diazabicyclo[3.2.1]octane in 51–73%
yield together with traces of the 2,5-diazabicyclo[2.2.2]octane. In
contrast, cycloaddition of this 3-oxidopyrazinium with methyl 2-phenyl
acrylate provided the [2.2.2] product in 40% yield. Herein, we show
that the 2,5-diazabicyclo[2.2.2]octanes were formed from the [3.2.1]
compounds via a Wagner–Meerwein rearrangement. Remarkably,
when acrylic acid and 2-phenylacrylic acid were employed as dipolarophiles,
novel tricyclic fused lactone-lactam systems were obtained in 71%
and 50% yields, respectively. The formation of these tricyclic compounds
can be rationalized via the mechanism described above followed by
lactonization of the 2,5-diazabicyclo[2.2.2]octane.