Pentanidium-Type Chiral Phase-Transfer Catalysts

Significance

The authors discovered a new chiral entity, pentanidium 4, as an efficient phase-transfer catalyst in the Michael additions of tert-butyl glycinate-benzophenone Schiff base 1 to various α,β-unsaturated ketones and esters. In the model reaction with ethyl acrylate, the enantiomeric excess obtained with pentanidium 4 (89%) was much higher than that with 5 (<5%). A gram-scale reaction with a low catalyst loading (0.05 mol%) has also been performed with high yield and selectivity, indicating the potential for practical applications of this methodology. Phosphoglycine ester analogues can also be utilized as the Michael donor, affording the enantioenriched α-aminophosphonic ester, which was further converted into the phosphonic analogue of (S)-proline.