Pyrrolidines bearing a quaternary α-stereogenic center. Part 2: Access to proline chimeras, stereoselective approach and mechanistic aspects

The present work describes the access to various proline chimeras bearing a quaternary α-stereogenic center, via the Duhamel ring contraction of heterocyclic enamines. Attempts to induce diastereoselectivity are reported. The ‘chiral enamine’ strategy afforded the required aminoaldehydes with diastereomeric ratios as high as 85:15.