Catalytic Asymmetric Synthesis of the <i>endo</i>-6-Aryl-8-oxabicyclo[3.2.1]oct-3-en-2-one Natural Product from <i>Ligusticum chuanxing</i> via 1,3-Dipolar Cycloaddition of a Formyl-Derived Carbonyl Ylide Using Rh<sub>2</sub>(<i>S</i>-TCPTTL)<sub>4</sub>
The reaction of a six-membered cyclic formyl-carbonyl ylide derived from α-diazo-β-ketoester with phenylacetylene derivatives under the catalysis of dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh2(S-TCPTTL)4, provides cycloadducts containing an 8-oxabicyclo[3.2.1]octane ring system in up to 97% ee. This represents the first example of an enantioselective 1,3-dipolar cycloaddition