Cobalt-catalyzed Alder-ene reaction

Allenes, while arguably underused in synthesis as a whole, have become popular functionalities in cycloisomerization chemistry and provide access to a wide variety of products. Ruthenium, cobalt, platinum, palladium, rhodium, and iridium catalysts are efficient in the transition metal-catalyzed Alder-ene reactions of allenes. 

Replacement of bis(l,2-diphenylphosphino)ethane by chiral phosphanes such as (— )-(25, 3 5)-bis(diphenylphosphino)butane or (- -)-(/ )- ,2-bis(diphenylphosphino)propane allows a highly enantioselective cobalt-catalyzed homo-Diels-Alder reaction (maximum 91% ee) between norbornadiene and monosubstituted alkynes. Similarly, the reaction of norbornadiene with phenylacetylene in the presence of catalytic amounts of tris(acetylacetonato)cobalt and (-l-)-bicyclo[2.2.1]hept-5-ene-2,3-diylbis(diphenylphosphane) leads quantitatively to the homo-Diels-Alder adduct with an ee of 98.4%. ... 

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