COBALT-MEDIATED RADICAL REACTIONS IN ORGANIC-SYNTHESIS - OXIDATIVE CYCLIZATIONS OF ARYL AND ALKYL-HALIDES LEADING TO FUNCTIONALIZED REDUCED HETEROCYCLES AND BUTYROLACTONES

Reactions between the CoI species derived from cobalt(III) salen (11) or cobalt(II) salophen (12) and (O-allyl) or (O-but-3-enyl) iodophenols lead to isolatable cobalt complexes, viz. (16) and (27), which can be converted into substituted benzofurans, i.e. (17) and (23), and benzopyrans, i.e. (28) and (34); similarly, interaction between compound (36) and CoI salen led in one step to 1,3-dimethylindole (37). Radical cyclisation of the acetal (38a) in the presence of CoI cobaloxime [from (10)] leads to the cis-ring-fused alkyl cobalt complex (42), which can be converted in a preparative manner into lactone (44) following 1,2-elimination [to (43)] and hydrolysis/oxidation, and into lactone (53) following insertion of molecular oxygen [to (50)], reduction [to (51)] and hydrolysis/oxidation.