Cyclooctyne (2) under bar underwent inverse electron demand Diels-Alder rea
ction with a variety of 3,6-diaryl-1, 2, 4, 5-tetrazines (1) under bar, giv
ing the corresponding pyridazines (3) under bar in excellent yields. LUMO (
1) under bar HOMO (2) under bar energy gaps between (1) under bar and (2) u
nder bar are obtained by semi-empirical molecular orbital calculations.