Synthesis of cobalt-substituted 1,3-diene complexes with unusual structures and their exo-selective Diels-Alder reactions

Article abstract of DOI:10.1021/ja00094a037

The synthesis and characterization (including crystallographic data) of several substituted-pyridine (Rpyr) cobalt bis(dimethylglyoxime) 1,3-butadiene complexes (R = H, tBu, 3,5-diMe, and N,N-dimethylamino) and their Diels-Alder reactions with a variety of dienophiles are reported here. The cobalt-carbon bonds in the Diels-Alder cycloadducts can be cleaved so that cobalt complexes as well as functionalized organic cycloadducts are recovered. Through these cobalt-carbon bond cleavage reactions, cobalt-diene complexes can serve as synthons for a variety of 1,3-dienes such as 1,3-butadiene, 2-(trimethylsiloxy)- 1,3-butadiene, iodoprene, (E)-1-methoxy-3-(trimethylsiloxy)-1,3-butadiene (Danishefsky's diene), and 1,2-dichloro-1,3-butadiene. The preparation of several cobalt-substituted 1,2- and 1,3-pentadiene complexes and highly exo-selective Diels-Alder reactions of the 1,3-pentadiene complexes are then discussed followed by demetalation reactions of these more highly substituted cobalt cycloadducts. These demetalation reactions maintain the stereochemical integrity found in the metal cycloadducts and also lead to cobalt recovery.