A kinetic study on radical cascade reactions of 1,6-enyne compounds was undertaken. The efficiency of the reaction depended on the presence of an ester group at the alkene unit, which clearly suggests that the addition of a tin radical was accelerated by the alpha,beta-unsaturated system. Stannolane formation progressed very quickly after a short induction period and completed within 12 min in the presence of Bu3SnH at 10(-2) M concentration at 110 degrees C. Product ratios between stannolane and exo-methylene compound depended on the concentration of Bu3SnH; a linear relationship was observed between the ratios of the two and the concentration of Bu3SnH. These results clearly indicate that the S(H)i process is irreversible. The slope of the graph allowed us to estimate the k(s) value, the S(H)i reaction rate at the tin atom, as 4.23 x 10(8) s(-1) at 303 K. The use of Bu2PhSnH for the reaction suggests that the S(H)i process partially progresses by the frontside attack of the vinyl radical, which generates a methylene radical that undergoes neophyl rearrangement to give methylene piperidine in a cis-selective manner.