FIGURE 2. Utility of Mannich product 3a in the highly enantioselective synthesis of natural products, pharmaceuticals, 
3-amino acids, and other building blocks.
From the following article:
Proline-catalysed Mannich reactions of acetaldehyde
Jung Woon Yang, Carley Chandler, Michael Stadler, Daniela Kampen & Benjamin List
Nature 452, 453-455(27 March 2008)
doi:10.1038/nature06740
KOt-Bu, potassium tert-butoxide.