Catalytic discrimination between inequivalent formyl groups was achieved using an aniline-Type acid-base catalyst for the regio-, diastereo-, and enantioselective intramolecular cross-Aldol reactions of enolizable dials. Although l-proline gave a mixture of the regio-and stereoisomeric products in the presence of an N-containing 1,6-dial, the aniline-Type catalyst afforded anti-3,4-disubstituted pyrrolidine in high regio-, and stereoselectivity beyond the background reaction, which led to the regioisomeric 2,3-disubstituted products. The mild reactivity of the aniline-Type amine facilitated catalytic discrimination between the inequivalent formyl groups. Kinetic isotope effect studies and reductive amination experiments suggested that the regioselectivity was controlled under the enamine-forming steps.
Baba, T., Yamamoto, J., Hayashi, K., Sato, M., Yamanaka, M., Kawabata, T., & Furuta, T. (2016). Catalytic discrimination between formyl groups in regio-and stereoselective intramolecular cross-Aldol reactions. Chemical Science, 7(6), 3791–3797. https://doi.org/10.1039/c5sc04594k