Radical cyclization cascades are powerful tools used to construct the complex
three-dimensional structures of some of society’s most prized molecules. Since its first use forty years ago, SmI2 has been used extensively for reductive radical
cyclizations. Unfortunately, SmI2 must almost always be used in significant excess thus raising issues of cost and waste. Here we have developed radical cyclization cascades that are catalyzed by SmI2 and that exploit a radical relay/electron-catalysis strategy. The approach negates the need for a super-stoichiometric co-reductant and requires no additives. Complex cyclic products, including products of dearomatization, containing up to four contiguous stereocenters are obtained in excellent yield. Mechanistic studies support a single-electron transfer radical mechanism. Our strategy provides a long-awaited solution to the problem of how to avoid the need for stoichiometric amounts of SmI2 and establishes a conceptual platform upon which other catalytic radical processes using the ubiquitous reducing agent can be built.