Development of a new cobalt catalyst system for the [4+2+2] cycloadditions of functionalized norbornadienes and butadiene

The combination CoX2/ligand/reducing agent/Lewis acid generates effective catalysts for the transition metal catalyzed [4 + 2 + 2] homo Diels-Alder reactions of norbornadienes with butadienes, leading to a new system which is highly effective at room temperature: CoI2/dppe/Zn/ZnI2. This catalyst shows broad functional group tolerance over a range of norbornadienes, and selectivity over other pathways such as butadiene polymerization and norbornadiene oligomerization. The Lewis acid effect in these cobalt-catalyzed [4 + 2 + 2] cycloadditions has also been probed.