Hendrickson reagent (triphenylphosphonium anhydride trifluoromethane sulfonate)

Abstract

(A) Xi and co-workers have described a methodology for the efficient synthesis of phenanthridines using the Hendrickson Reagent under mild conditions. The method exploits a Hendrickson reagent initiated cascade annulation to achieve a highly reactive imido-carbonium intermediate which undergoes subsequent intramolecular Friedel-Crafts reaction. This method tolerates a wide range of functional groups. Phenanthridines are a core structure of many naturally occurring bioactive alkaloids.11 (B) Xu and colleagues have reported a flexible protocol involving a two-step strategy to assemble 11H-indolo[3,2-c]quinoline starting from acyclic alkyne substrates. Hendrickson reagent is used as the second step after gold(III)-catalyzed 5-endo-dig cyclisation to promote regioselective 6-endo cyclisation under mild conditions. Naturally occurring alkaloids containing the 11H-indolo[3,2-c] quinoline scaffold have diverse biological properties.12 (C) Isoquinoline and β-carboline are important scaffolds in naturally occurring and synthetic bioactive alkaloids. As an alternative to the Pictet-Gams reaction, Wu and Wang have developed a one-pot protocol to access isoquinoline and β-carboline. The Hendrickson reagent is used to trigger cyclization which is then followed by oxidative aromatization.13 (D) Xu and co-workers have described an efficient synthesis of furoquinolinones using a Hendrickson reagent initiated cascade annulation involving the conversion of stable aniline-amides to the corresponding highly reactive imido-carbonium intermediates.14 (E) Mossotti and Panza showed that the Hendrickson reagent was able to efficiently perform dehydrative glycosylation of 1-hydroxyglycosyl donors. The reaction occurs under mild conditions through an anomeric oxophosphonium intermediate detected through nuclear magnetic resonance spectroscopy.15 (F) The camptothecin family of alkaloids attracts considerable attention due to their anticancer activities. Zhou et al. showed a total synthesis of camptothecin, in which Hendrickson reagent was used to trigger a mild and efficient cascade reaction that was subsequently followed by a highly enantioselective Sharpless asymmetric (AD) dihydroxylation.16 This method achieved much higher yields than the method previously described by Fortunak, in which trimethyloxonium fluoroborate was used as the activating agent.17 © Georg Thieme Verlag KG · Stuttgart · New York.