Introduction
Pyrrolidine-2-carboxylic acid commonly known as l-Proline
(I) has shown, in recent times, excellent
catalytic activity, in catalyzing a wide variety of reactions such
as aldol,
[1]
[2]
Mannich,
[3-5]
[10-12]
Michael,
[6-9]
in a highly enantioselective
manner. These reactions have produced a variety of useful chiral
materials for organic synthesis.
Most of the l-Proline (I) catalyzed
reactions are believed to involve enamine (II)
as key intermediate in its catalytic cycle (Scheme
[1]
).
Scheme 1 Proline - catalytic
cycle for aldol reaction.