The three-component Petasis borono-Mannich reaction starting with easily accessible N-protected α-amino aldehydes produces efficiently and diastereoselectively 1,2-trans-diamines with an enantiomeric excess of up to 98%.

The Petasis borono‐Mannich (PBM) process with easily accessible N‐protected α‐amino aldehydes produces 1,2‐trans‐diamines diastereoselectively with an enantiomeric excess up to 98 %. The protecting group on the nitrogen atom had a decisive influence on both the yield and the enantiomeric purity of the condensation products, and the best results were obtained with sulfonamide derivatives [nosyl (Ns), tosyl (Ts), and mesyl (Ms)]. To get a better understanding of the influence of the protecting group, we investigated the mechanism of the borono‐Mannich reaction through DFT calculations.