New Pathway to C2‐Symmetric Atropoisomeric Bipyridine N,N′‐Dioxides and Solvent Effect in Enantioselective Allylation of Aldehydes

The [2+2+2] cyclotrimerization of 1,7,9,15‐hexadecatetrayne with nitriles catalyzed by dicarbonylcyclopentadienylcobalt(I) opened a new pathway for the synthesis of C₂‐symmetrical bis(tetrahydroisoquinolines) that were used as starting material for the preparation of axially chiral bipyridine N,N′‐dioxides. The N,N′‐dioxides (1 mol%) were found to be highly catalytically active and enantioselective (up to 83% ee) for the asymmetric allylation of aldehydes with allyl(trichloro)silane in various solvents. In addition, a dramatic solvent effect was observed where the use of different solvents induced opposite chiralities of the product with the same enantiomer of the catalyst, e.g., 65% ee (S) in acetonitrile (MeCN) vs. 82% ee (R) in chlorobenzene.