| SYNTHESIS |
One way to prepare -lactams is through coupling of alkynes with nitrones. Called the Kinugasa reaction, this route to lactams can yield multicyclic systems if the coupling occurs intramolecularly, according to recent work by Ryo Shintani and Gregory C. Fu at MIT. With copper/phosphaferrocene-oxazoline catalysts, synthesis of two new rings is achieved in up to 74% yield and up to 91% enantiomeric excess [Angew. Chem. Int. Ed., 42, 3921 (2003)]. Shintani and Fu also show that further complexity in the product can be introduced by intercepting a key intermediate with an electrophile added to the reaction mixture. Thus, the heterocyclic alkyne-nitrone substrate shown (Ar = carboethoxyphenyl) in the presence of allyl iodide is converted in one cyclization-alkylation sequence to the alkylated tricyclic -lactam in 70% yield and 90% ee. |
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