Prolina – pospolity aminokwas wyjątkowy katalizator. Część II, Międzycząsteczkowa kondensacja aldolowa Proline as a common amino acid and an exceptional catalyst. Part II, Intermolecular aldol reaction
Proline in organic synthesis is used as a small molecular organocatalyst.
In a catalytic act proline, similarly to an enzyme, activates reagents, stabilizes transition
state and influences an orientation of substrates [1–12]. Proline works as aldolase
I (so called microaldolase I). In comparison with other amino acids it shows
exceptional nucleophilicity which makes imines and enamines formation easier.
In the intermolecular aldol reaction proline was used for the first time by List
and co-workers (Scheme 1) [3, 9, 20]. Since then an immense progress has been
observed in this field. Several aldolization reactions were performed in the presence
of proline. Reactions of this type proceed between the donor (nucleophile) and
the acceptor (electrophile).
In aldol reaction the donors can be both ketones and aldehydes which next
are condensed with ketones and aldehydes acting as electrophiles (Scheme 2–18;
Tab. 1–7) [21–72]. The presence of proline ensures not only high yield of homo- and
heteroaldolization but mainly enables conducting enantio- and diastereoselective
synthesis. Intermolecular proline-catalyzed aldol condensation proceeds according
to enamine mechanism. Anti-aldols, which make a valuable source of intermediates
in the synthesis of important biologically active compounds, are mainly obtained
in this reaction [35–44, 54, 58, 62, 63, 68, 69, 71].
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