Radical cyclization reactions are important and versatile tools in organic synthesis. Most of these reactions include the use of toxic tin hydrides and a heavy element (typically iodine, bromine, selenium, or sulfur) to form the initial organic radical. The replacement of stoichiometric tin hydride reactions with catalytic reactions involving non-toxic reagents would render radical cyclizations more useful for pharmaceutical applications. We have developed radical cyclization reactions that use transition-metal hydrides to donate hydrogen atoms to substituted dienes, forming organic radicals that can then cyclize. In addition, performing the reaction in a hydrogen atmosphere regenerates the transition-metal hydride from the resulting metal radical, making the reaction catalytic. A model compound study was used to determine the rates of hydrogen atom transfer to variously substituted olefins. This newly developed method for radical cyclization reactions is not only tin-free but catalytic.