Copper-Catalyzed Skeletal Rearrangement of O-Propargylic Aryloximes into Four-Membered Cyclic Nitrones - Chirality Transfer and Mechanistic Insight
摘要:
Copper-catalyzed skeletal rearrangement of O-propargylic aryloximes (E)-1 were carried out to afford the corresponding four-membered cyclic nitrones 2 in good to excellent yields. The optimal reactions conditions of the highly regioselective reactions involved the use of [CuCl(cod)](2) in acetonitrile at 70 degrees C. In the case of (Z)-1, however, the reaction proceeded in the absence of the copper catalysts to afford the identical compound 2 in good yields. Furthermore, the reactions were also carried out using chiral substrates (R)-1 in the presence of Cu catalysts to afford (R)-2 with good levels of chirality transfer.
The newly prepared bipyridine (S,S)‐2 was then tested as a chiral ligand in metal‐catalyzed enantioselectivereactions. Out of the studied reactions the most promising results were obtained in epoxide ring opening (82% yield, 98% ee) and Mukaiyama aldolreaction (>96% yield, 99/1 dr, 92% ee). In the case of Mukaiyama‐aldolreaction as well as in the Michael addition, novel ligand 2 proved its robustness