Organocatalysed Asymmetric Direct Mannich Reaction of Acetophenone Derivatives and Dibenzo[b, f][1, 4]oxazepines with Azetidine‐2‐carboxylic Acid. Issue 10 (26th August 2014) - Ren, Yuan‐Yuan
Abstract An enantioselective direct Mannich reaction of different acetophenone derivatives with various substituted seven‐membered cyclic imines using (S)‐azetidine‐2‐carboxylic acid as an organocatalyst is described, which provides an efficient access to optically active 11‐substituted‐10, 11‐dihydrodibenzo[b, f][1, 4]oxazepine derivatives with 87–95 % ee. For α, β‐unsaturated ketone benzalacetone, the desired Mannich product was obtained with 72 % ee. A plausible transition state is established to explain the observed absolute stereochemistry of the Mannich products. The reaction can also be performed on a gram scale with no adverse effects on the yield and enantioselectivity. Furthermore, some simple transformations involving the Wittig olefination and the decarboxylative reduction of the Mannich products were performed.