The Sommelet-Hauser rearrangement of N-benzylic ammonium ylides generated from tetraalkylammonium salts is an interesting and useful transformation in organic synthesis that can provide easy access to ortho-substituted aromatic compounds. The base-induced rearrangement of an N-chiral-N-benzylic proline-derived ammonium salt or N-benzylic amino acid (−)-8-phenylmenthol ester-derived ammonium salts is shown to proceed in excellent yields with perfect levels of diastereoselectivity without any detectable amount of the [1,2]Stevens rearrangement product. A solution of potassium tert-butoxide in THF was shown to remarkably enhance the base-induced Sommelet-Hauser rearrangement of N-benzylic amino acid-derived ammonium salts. The reaction proceeds under mild conditions with minimal competition from the [1,2]Stevens rearrangement. These methods provide efficient access to α-aryl-α-amino acid, α-aryl-β-amino acid, and α-arylpipecolinic acid derivatives.