The reaction taking place is between a simple aldehyde, such as propionaldehyde, and an imine derived from ethyl glyoxylate and "p"-methoxyaniline (PMP = paramethoxyphenyl) catalyzed by ("S")-proline in dioxane at room temperature. The reaction product is diastereoselective with a preference for the syn-Mannich reaction 3:1 when the alkyl substituent on the aldehyde is a methyl group or 19:1 when the alkyl group the much larger pentyl group. Of the two possible "syn" adducts ("S","S") or ("R","R") the reaction is also enantioselective with a preference for the ("S","S") adduct with enantiomeric excess larger than 99%. This stereoselectivity is explained in the scheme below.