Tandem cycloaddition/radical cyclization is an effective strategy for the rapid assembly of a wide variety of ring systems. To set up the reagents for this sequence, it is necessary to include a potential radical site in one of the two cycloaddition partners, located at an appropriate distance from a new double bond that will be formed in the cycloaddition step. Examples in which the cycloaddition step is [4+ 21 or [3+ 21 and in which the radical ...