Free radical allylations of α-seleno carbonyl compounds with tributyl-2,4-pentadienyltin, -β-methallyltin, -crotyltin, and -prenyltin, are described. Such successful C-C bond formations, in particular with the crotyltin and the prenyltin, are owing to the high reactivity of the α-carbon radical, generated from α-seleno carbonyl compounds, toward allylic tin compounds. These reactions provide a powerful, convenient and efficient method for α-monoallylation of carbonyl compounds.