Synthesis of novel carbo- and heteropolycycles. Part 30. 1,3-Dipolar cycloaddition of nitrile functions with some selected nitrones. Efficient synthesis of 2,3-dihydro-1,2,4-oxadiazole derivatives
A practical reactivity of nitrile groups as dipolarophiles in 1,3-dipolar cycloadditions with 4-azahomoadamant-4-ene N-oxides 1 and 2, 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide 8 and N-benzylidenephenylamine N-oxide 10 is reported. Benzonitriles 3c–i reacted with these nitrones upon heating for more than 12 h to afford the corresponding 2,3-dihydro-1,2,4-oxadiazole derivatives. The reaction of acetonitrile 3b with nitrone 1 required a prolonged reaction time (15 days). However, the reaction of an activated nitrile, methyl cyanoformate 3j, proceeded smoothly under milder conditions (25 °C for 1, 2 and 8, and 80 °C for 10).