Alternative Route to Aza-MBH Products

The authors have developed an asymmetric Mannich-type reaction of stabilized phosphorus ylide 1 and both aromatic and aliphatic N-Boc-protected aldimines 2. The reaction is mediated by the readily available and recyclable chiral bisthiourea catalyst 3. Subsequent Wittig reaction of the Mannich products 5 with formaldehyde furnishes N-Boc-β-amino-α-methylene carboxylic esters 4 in good to high yields and enantio­selectivities.