Recent progress in the asymmetric organocatalysis

In the early 1970s, intramolecular aldol reaction catalyzed by proline was reported by Hajos et al., and its intermolecular version was discovered by List, Barbas, and Lerner in 2000. In the same year, MacMillan reported the asymmetric Diels-Alder reaction catalyzed by organocatalyst by lowering the LUMO energy of enones by the formation of iminium salt. After these two seminal papers, chiral small organic molecules have been widely employed in asymmetric synthesis because they have several advantages over the conventional transition metal based catalysts. Organic catalysts are inexpensive, readily available, and non-toxic. They are not sensitive to moisture and oxygen. The products are free from the contamination of metals. Because of these advantages, this field has been expanding so rapidly. Though there are so many asymmetric reactions catalyzed by organocatalysts, this article briefly summarizes the recent progress in the following reactions because of the limitation of space: Aldol reaction, Mannich reaction, Michael reaction, functionalization of a-position of carbonyl compounds, cycloaddition reactions such as Diels-Alder reaction, [3 + 2] cycloaddition reaction, and [4 + 3] cycloaddition reaction, allylation, Morita-Baylis-Hillman reaction, epoxidation, and phase-transfer reaction.