β-Silicon Effect Enables Metal-Free Site-Selective Intermolecular Allylic C–H Amination

α-Amino silanes and their derivatives play pivotal roles across diverse applications, yet their current synthetic methods often entail intricate functional group manipulations. Despite the widespread use of allyl silanes as carbon nucleophiles in organic synthesis, their participation in allylic C–H functionalization has been underexplored. Herein, we unveil a metal-free intermolecular C–H amination of allyl silanes facilitated by the β-silicon effect. This protocol yields α-amino silanes with exceptional site selectivity. Notably, a wide array of secondary and tertiary α-amino silanes are synthesized in high yields without desilylation, owing to the mild reaction conditions and a reaction pathway. Mechanistic elucidations highlight the activation effect of the silyl moiety on alkenes, alongside its stabilizing influence on adjacent developing positive charges, which selectively drives a closed transition state, ensuring site selectivity.