Calcium-based chiral catalysts

Calcium isopropoxide complexed to the simplest Ph-BOX ligand serves as a Bronsted base and chiral catalyst for rendering glycine t-butyl ester into a nucleophile toward acrylic esters. 

Ikegami et al. reported an asymmetric Morita—Baylis—HUlman reaction using a BlNOL-calcium complex as a chiral Lewis acid and tributylphosphine as an achiral Lewis base (Scheme 2) [24]. It was found that an active calcium aryloxide catalyst could be prepared from Ca(0 Pr)2 and (f )-BINOL in THF. The reaction of cyclopentenone with 3-phenylpropionaldehyde was tested in the presence of the calcium complex, and the desired Morita-Bayhs-Hillman adduct was obtained in 62 % yield with 56 % ee. 

Saito, S., Tsubogo, T., Kobayashi, S. (2007). Chiral calcium complexes as Brpnsted base catalysts for asymmetric addition of a-amino acid derivatives to a,f)-unsaturated carbonyl compounds. Journal of the American Chemical Society, 129, 5364-5365. 

---