Advances in Aza-Claisen-Rearrangement-Induced Ring-Expansion Strategies

The aza-Claisen rearrangement, also known as the 3-aza-Cope rearrangement, has attracted significant attention because it can be used as a complimentary method to access a diverse range of useful organic molecules. The presence of a nitrogen atom at the 3-position enables the tethering of various-sized azacycles, thereby giving ring-expansion strategies that take advantage of the aza-Claisen rearrangement a distinct advantage compared to other [3,3]-sigmatropic rearrangements. Recent advances in aza-Claisen rearrangements have facilitated otherwise-inaccessible ring expansions in a highly stereoselective manner. The utility of aza-Claisen-rearrangement-induced ring-expansion strategies has been exemplified in the synthesis of a diverse range of natural products. This Focus Review summarizes recent advances in aza-Claisen-rearrangement-induced ring-expansion strategy, in particular applications in the synthesis of bioactive alkaloids.