of organotinmaleates to undergo Diels–Alderreactions with a range of dienes has been examined. Crystalline adducts have been obtained from 2,3-dimethylbuta-1,3-diene with triphenyltin methyl maleate and from cyclopentadiene with triphenyltin methyl maleate, tributyltin methyl maleate, dibutyltin bis(methyl maleate), and dibutyltin maleate. The products expected from the Diels–Alderreactions of 2