Asymmetric Sommelet-Hauser rearrangement of N-benzylic ammonium salts.

The Stevens and Sommelet–Hauser rearrangement of ammonium ylides are known as useful transformations for organic synthesis because they convert a readily accessible C–N bond into a new C–C bond. The Stevens rearrangement has been widely used for the asymmetric synthesis of α-amino acid derivatives, whereas the Sommelet–Hauser rearrangement is much less common because the Sommelet–Hauser rearrangement usually competes with the [1,2] Stevens rearrangement. For example, the base-induced rearrangement of carbonyl-stabilized ammonium ylides such as Nbenzylic-α-amino ester-derived ammonium ylides almost exclusively undergoes the [1,2] Stevens rearrangement to give the α-benzylated amino acid derivatives. For these reasons, synthetic applications of the Sommelet–Hauser rearrangement and its asymmetric versions have been limited. Herein, we wish to report the unique example of the Sommelet–Hauser rearrangement of carbonyl-stabilized ammonium ylides which are not accompanied by the [1,2] Stevens rearrangement to a detectable extent.