Sequential Pd-Catalyzed Asymmetric Allene Diboration/α-Aminoallylation

Significance

This protocol utilizes the chiral diboron intermediate previously reported by this group as a ‘reagent’ for allylation of ammonia derived imines. Two methods can be used, often with similar yields and high chirality transfer. While the direct use of the aldehyde with NH₄OAc is attractive and successful in many instances, the yields are significantly diminished when R¹ = Cy and R² = Ar. The authors were able to isolate the anticipated Z-intermediate from the reaction medium and performed an X-ray crystal structure analysis to identify the stereochemistry. The same intermediate was also used to show that the vinylborane could be applied in Suzuki-Miyaura cross-coupling reactions or simply protonated to form the disubstituted alkene.