Mefa-pyrrolophane

A platinum- and Lewis acid catalyzed enyne metathesis was used as the key step in the formal total synthesis of antibiotics streptorubin B and metacycloprodigiosin by A. Furstner. The electron-deficient enyne was cyclized with either a platinum halide or a hard Lewis acid (e.g., BF3-OEt2) to the desired mefa-pyrrolophane core of the target molecules. A few more steps completed the formal synthesis. 

In the laboratory of A. Ftirstner, a practical synthesis of the immunosuppressive aikaioid metacycioprodigiosin and its functional derivatives was developed. Toward the end of the synthetic sequence a mefa-pyrrolophane (3-keto ester was decarboxylated under standard Krapcho conditions. The substrate was dissolved in wet DMSO, and two equivalents of sodium chloride were added and the reaction mixture was heated to 180 °C to afford the desired meta-pyrrolophane ketone in excellent yield. This ketone functionality was first converted to an ethyl group and then the product was advanced to metacycioprodigiosin. 

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See also in sourсe #XX -- [ ]

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