Diels–Alder cycloaddition of 2-azadienes to methyl 2-(2,6-dichlorophenyl)-2H-azirine-3-carboxylate in the synthesis of methyl 4-oxo-1,3-diazabicyclo[4.1.0]heptane-6-carboxylates

A number of fused 4-oxo-1,3-diazabicyclo[4.1.0]heptane-6-carboxylates, a new type of compound, have been obtained by Diels–Alder cycloaddition between nucleophilic 2-azadienes and an electrophilic 2H-azirine. The reactions are completely endo- and regioselective, the azirine being added by its less hindered face to the diene. There are two isomers and formed from dienes due either to isomerization of the cycloadducts and or by isomerization of the CN bond of the diene during the reaction. The isomer is formed from diene , and a single diastereoisomer structure is formed from dienes . Some pyrimidones , /, , , have been hydrolyzed leading to functionalised aziridines , and .