CASCADE COBALT GROUP TRANSFER - RADICAL TRAPPING - TANDEM RADICAL CYCLIZATION REACTIONS IN SYNTHESIS

Cobalt mediated tandem radical cyclisations, viz (1) --> (3), (5) --> (7), (10) --> (13), can be carried out in sequence with isolation of intermediate organocobalt reagents, i.e. (2), (6), (11), or alternatively in a 'one-pot' operation. In the presence of reactive radical trapping agents (e.g. O-3(2), TEMPO) the intermediate organocobalt reagents undergo functional group exchange, le.g. (11) --> (15) and (14) respectively], whereas in the presence of less reactive styrene, a cascade of cobalt group transfer-radical trapping-tandem radical cyclisation - dehydrocobaltation reactions result allowing, for example, the five step 'one-pot' synthesis of (12) from (10) in 20% overall yield.