In general, longer reaction times correlated with lower isolated yields, which suggests that the radical group transfer is competing with a slower side reaction. To investigate this hypothesis, the reaction with 4k was performed in MeCN-d3/CD3OD 9:1. Upon full consumption of the starting material, as indicated by TLC, the reaction mixture was directly subjected to analysis by H NMR with an internal standard. The yield at this stage was 40%, with no sign of elimination or other decomposition products, despite the reaction being run in a closed system. H NMR analysis was repeated after acidic desilylation, and after aqueous workup. The yield did not change during desilylation, while a further 25% of the material was lost during the workup. As the majority of product loss occurs during the radical group Scheme 2. Radical group transfer of vinyl silanes a a The products are organized in five categories, depending on the position of the iodide before the radical reaction. Reaction scale: 0.30 mmol. transfer reaction, and no side products are observable by H NMR, we postulate that degradation can occur through polymerization when long reaction times are required. Control experiments with 4n verify that the starting material and product only undergo minor background degradation under the reaction conditions (see the Supporting Information). Thus, we reason that polymerization is a competing pathway for the radical group transfer reaction itself.