“…In analogy to the reaction of 1 with 3, MNDO calculations performed with the parent compound of the series 2 also predict a LUMO,,,,, -HOMO,,,,,,,,,,-controlled cycloaddi-*) The geometries used for the computer-aided graphical representation (Atari mega STcomputer; Chem Graph programme) were deduced from Biichi-Dreiding models and X-ray crystallographic data of structurally related compounds [17]. The 1,4-dihydropyridazine ring has the boat conformation.…”