The total synthesis of optically active annotinine

Abstract

The total synthesis of the first Lycopodium alkaloid annotinine in the optically active form is described. The key step in this synthesis was the photochemical addition of allene to the tricyclic vinylogous imide (3) which yielded the photoadduct (6).

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…Als synthetisches ¾quivalent für Propylen oder Keten dient in der [2+2]-Photocycloaddition mitunter Allen. Anwendungen finden sich in den Synthesen von (AE )-Atisin, [293] (À)-Annotinin, [294] (AE )-Allocyathin B 3 , [295] (À)-Cyathin A 3 , [296] (AE )-Heliannuol D [297] und (AE )-Pentalenen. [298] Weitere intermolekulare Zugangswege zum racemischen und zum enantiomerenreinen Kelsoen (216) [299] wurden ebenso beschrieben wie eine der oben gezeigten Strategie folgende Synthese des strukturell verwandten (À)-Sulcatin G. [300] Ein alternativer Zugang zu (AE )-Kelsoen (216) bediente sich der intramolekularen Cu-katalysierten [2+2]-Photocycloaddition (Schema 57).…”

Bioactive cyclobutane-containing alkaloids

“…Annotinine (5) has been isolated for the first time from L. annotinum (Lycopodiaceae, Clubmoss family) by Manske and Marion [19]. Complete structure, stereochemistry, and synthesis were reported a decade later [20][21][22][23][24][25][26][27]. More recently, this alkaloid was isolated from L. annotinum [28][29][30] and other Lycopodiaceae species: L. phlegmaria [31]; L. selago [32]; L. flabelliforme [33]; L. obscurum [33]; genus Huperzia; and related genera Phlegmariurus, Lycopodium, Lycopodiella, Palhinhaea, Diphasiastrum, and Lycopodiastrum [34].…”

The crystal and molecular structure of a tetracyclic bromobenzoate, C21H23O2Br

“…Wiesner, Poon, Jirkovsk~ & Fishman (1969) proposed that the stereochemistry of this photo-addition is controlled by the tendency of the excited state to exist preferentially in the most stable configuration. The excited state was assumed to have carbonium character in the ~ position to the carbonyl group and an orbital with an electron pair in the fl position.…”