Asymmetric Hydrovinylation of Vinylindoles. A Facile Route to Cyclopenta[g]indole Natural Products (+)-cis-Trikentrin A and (+)-cis-Trikentrin B

摘要: Vinylindoles undergo Ni(II)-catalyzed asymmetric hydrovinylation under very mild conditions (−78 °C, 1 atm ethylene, 4 mol % catalyst) to give the corresponding 2-but-3-enyl derivatives in excellent yields and enantioselectivities. Hydroboration of alkene oxidation an acid, followed by Friedel–Crafts annulation, gives indole-annulated cyclopentanone that is a suitable precursor for syntheses cis-trikentrins all known herbindoles. For example, from 4-ethyl-7-vinylindole converted into (+)-cis-trikentin A four steps (Wittig reaction, isomerization, diastereoselective hydrogenation, nitrogen deprotection). The previous synthesis this molecule (S)-(−)-malic acid involved more than 20 preparative HPLC separation diastereomeric intermediates.