The ene reaction of some allylic hydrocarbons, and the metallo-ene rea
ction of some allyltin compounds, with 1,3,4-triazoline-2,5-diones or
with diethyl azodicarboxylate as enophiles, in diethyl ether are stron
gly catalysed by lithium perchlorate. Azobenzene, on the other hand, r
eacts slowly with alkyltin compounds, undergoing hydrostannation. The
reaction of cholesterol or of tributylallyltin with singlet oxygen is
subject to a smaller catalysis.