Search

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. [ABSTRACT FROM AUTHOR]

3-Substituted-2 H-1,4-benzoxazines undergo a highly enantioselective direct Mannich reaction with acetone in the presence of an L-proline catalyst at room temperature. The corresponding N-heterocycles with α-tetrasubstituted carbon stereocenters were obtained in good yields (48-92%) and excellent enantioselectivity (up to >99% ee). Furthermore, a novel modification involving the diastereoselective reduction of the Mannich adduct was carried out leading to the formation of a 1,3-amino alcohol with a chiral tetrasubstituted carbon stereocenter in high yield. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Direct Organocatalytic Asymmetric Mannich Addition of 3-Substituted-2H-1,4-benzoxazines: Access to Tetrasubstituted Carbon Stereocente" by Y.Q. Wang, and others, published in the "Advanced Synthesis and Catalysis" in 2013 issue.

Optically active dibenzo[b,f][1,4]oxazepine derivatives [(R)-(III) and (R)-(V)] are efficiently and enantioselectively synthesized. [ABSTRACT FROM AUTHOR]