We reported recently that Schiff base 1 (Figure 1) is a remarkably general catalyst for the hydrocyanation of aldimines [1] and ketoimines,[2] producing Strecker adducts in> 90% ee for most substrates examined (Equation 1).[3] This catalyst was identified and optimized from a parallel library of Schiff base derivatives that was synthesized and screened on solid phase.[1, 4]

Resin-bound catalyst 1a was identified as affording optimal enantioselectivity for a model imine hydrocyanation reaction, and was applied successfully to the enantioselective synthesis of Strecker adducts on preparative scale. This polymer-supported catalyst displayed important practical features, as it could be reisolated readily by simple filtration and recycled repeatedly.[1, 2] On the other hand, the homogeneous analogue 1b was found to display substantially higher reactivity and to induce slightly improved enantioselectivity (1±3% ee) in the hydrocyanation of most substrates, even if used at substantially lower loadings.[5] These advantages were offset, however, by the fact that 1b was more difficult to prepare than resin-bound 1a.[6] Our previously reported synthesis [2] provided 1b in 53% overall yield and included three chromatographic purifications (Scheme 1).