The heterodimeric indole/coumarin natural product exotine B was synthesized for the first time. The carbon skeleton of the natural product was formed rapidly by a palladium-catalyzed Suzuki cross-coupling reaction and a gallium-catalyzed three-component [4 + 3] cycloaddition reaction. An alternative biosynthesis of exotine B is proposed based on the total synthesis. Improved syntheses of coumarin natural products gleinadiene and coumurrayin are also reported.

Sinoracutine is a recently isolated alkaloid with unusual stereochemical and biological properties. It features an unprecedented tetracyclic 6/6/5/5 skeleton that bears an N-methylpyrrolidine ring fused to a cyclopentenone. Interestingly, both enantiomers of sinoracutine have been independently isolated from the same plant, yet the molecule does not appear to occur as a racemate. Here, we present a short synthesis of (-)-sinoracutine that relies on a highly diastereoselective Pauson-Khand reaction and a Mandai-Claisen reaction to install the quaternary stereocenter. Our work establishes the absolute configuration of the levorotatory isomer and suggests that the optical purity of sinoracutine varies in nature due to its gradual racemization. Experimental evidence supports this proposal, and a plausible mechanism for the racemization is provided.

Allylboron reagents are popular in synthesis owing to their versatility and the predictable stereochemical outcomes of their reactions with carbonyl compounds. Herein, we describe the synthesis of (Z,Z)-hexadienyl bis-boronate 1, a configurationally stable, crystalline, and easy to handle compound, which represents a class of bis-allylic boron reagents with heretofore untapped synthetic potential. In combination with a chiral phosphoric acid catalyst, the reagent can be employed for the enantioselective allyl transfer reaction to a variety of one-pot transformations, enabling swift access to functionalized 1,n-diols. The in situ conversion of the reagent into the corresponding bis-borinic ester allows for the direct and diastereoselective two-fold allyl transfer to aldehydes. This affords C - or C -symmetric stereotetrads containing a 1,4-diol moiety for natural product synthesis. The usefulness of our method was demonstrated with a short synthesis of the lignan (±)-neo-olivil.

Sinoracutin ist ein Alkaloid mit ungewçhnlichen strukturellen und biologischen Eigenschaften. Es besteht aus einem einzigartigen tetracyclischen 6/6/5/5-Gerüst mit einem N-Methylpyrrolidinring,d er mit einer Cyclopentenoneinheit verbunden ist. Interessanterweise wurden beide Enantiomere von Sinoracutin unabhängig voneinander aus derselben Pflanze isoliert, allerdings nicht in racemischer Form. Hier wird eine Synthese von (À)-Sinoracutin beschrieben, die auf einer diastereoselektiven Pauson-Khand-Reaktion und einer Mandai-Claisen-Umlagerungz ur Einführung des quartären Stereozentrums beruht. Die vorliegende Arbeit bestätigt die absolute Konfiguration des laevorotatorischen Isomers und legt nahe,d ass die Enantiomerenreinheit des Naturstoffs infolge langsamer Racemisierung variiert. Diese Vorhersage wird durch experimentelle Befunde gestützt, und plausible Mechanismen fürdie Racemisierung werden vorgeschlagen. Schema 1. Strukturvielfalt der von Reticulin abstammenden Alkaloide.

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