The side arm strategy for chiral catalyst design by assembling one or two pendent groups on the classic bisoxazoline ligands has proved efficient and powerful. Based on this strategy, a series of trisoxazoline (TOX) and side armed bisoxazoline (SaBOX) ligands were synthesized and employed in a variety of asymmetric catalytic reactions. In this lecture, we will report some examples of our recent results on this subject. For examples, with Cy-SaBOX/Cu(II) catalyst, highly diastereo- and enantioselective hetero-Diels–Alder reactions of β,γ-unsaturated α-ketoesters with cyclic enamines was developed, leading to an effective access to the synthesis of chiral bicyclic N,O acetals. An enantioselective construction of cyclobutanes was promoted by iPr-SaBOX ligand, which provided a new and concise approach to the total synthesis of (+)-Piperarborenine B; in the presence of Cy-TOX ligand. Asymmetric ring opening of D−A cyclopropanes with water, as well as asymmetric [4+3] annulation of donor−acceptor cyclopropanes with dienes were realized respectively, affording the correspondingγ-substituted GBH derivatives and [n,5,0]carbobicycles in high yields with excellent levels of enantioselectivity. By employing iPr-SaBOX/Cu(II) catalyst, highly diastereoselective and enantioselective formal [4 + 3] cycloaddition of donor−acceptor cyclobutanes with nitrones was also demonstrated.

Asymmetric catalytic reactions: Recent use of TOX and SaBOX ligands

254th National Meeting (2017)

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