The intramolecular hydrosilylation of (4-pentenyl)hydrosilanes with transitionmetal salt catalysts afforded five- and six-membered ring-closure products in high yields, with the former predominating. This has been rationalized in terms of a reaction scheme based on the Harrod—Chalk mechanism in which both Si-metal and C-metal bonds were involved. The seven-membered intermediate leading to the six-membered