Synthetic methods. Part (i): Free-radical reactions

Abstract

Two topics continue to dominate radical chemistry; the search for cleaner, more efficient methods to generate radicals, and improving enantioselectivity in radical reactions. The use of photoredox catalysts that rely on visible light to promote the formation of alkyl radicals has great potential to allow radical chemistry to gain more widespread acceptance. The research of Stephenson and others has shown that this chemistry can mediate many traditional radical transformations. Three groups have reported truly green methodology for the formation of acyl radicals that simply requires water and air. MacMillan’s enantioselective organocatalytic radical chemistry continues to push the boundaries of asymmetric synthesis; this year has seen it used in a radical-ion crossover cascade for the synthesis of carbocycles and in a number of remarkable polyene cascade cyclisations. The latter includes a hexacyclisation that installs 11 contiguous stereocentres with high diastereo- and enantioselectivity.