Enantioselective Organocatalytic Syntheses and Ring-Expansions of Cyclobutane Derivatives

The progress in enantioselective organocatalysis have enabled efficient and highly stereoselective syntheses of cyclobutane derivatives, through (2 + 2) annulation reactions, overcoming the geometrical constraints inherent to these small cyclic molecules. More importantly, and taking advantage of their strain-releasing fragmentation, some cyclobutane derivatives, especially cyclobutanones and cyclobutenones, can now be regarded as versatile four-carbon atoms units amenable to the enantioselective construction of larger rings by (4 + n) annulation reactions to produce, five-, six-, seven-and eightmembered cyclic products. These recent developments concerning the enantioselective synthetic chemistry of cyclobutane derivatives under organocatalytic conditions are reviewed herein.