Direct synthesis of γ-pyrones by electrophilic condensation of β-ketoesters
作者:Catarina A. B. Rodrigues、Antonio Misale、Florian Schiel、Nuno Maulide
DOI:10.1039/c6ob01884j
日期:——
Triflic anhydride is a versatile electrophile that is able to activate poor nucleophiles. Herein, we show that readily available β-keto esters are activated by Tf2O furnishing γ-pyrones. Mechanistic studies suggest that this transformation proceeds via a double triflation, formation of an oxocarbenium intermediate and dealkylation promoted by a crucial nitrile additive.
Regiodivergent Hydration–Cyclization of Diynones under Gold Catalysis
作者:Marta Solas、Miguel A. Muñoz、Samuel Suárez-Pantiga、Roberto Sanz
DOI:10.1021/acs.orglett.0c02892
日期:2020.10.2
Skipped diynones, efficiently prepared from biomass-derived ethyl lactate, undergo a tandem hydration–oxacyclization reaction under gold(I) catalysis. Reaction conditions have been developed for a switchable process that allows selective access to 4-pyrones or 3(2H)-furanonesfrom the same starting diynones. Further application of this methodology in the total synthesis of polyporapyranone B was demonstrated
Brønsted acid catalyzed tandem cyclization was found to be highly effective for the preparation of a series of polysubstituted 4-pyrones from diynones (yield up to 99%). 4-Pyridone and 3-pyrrolone derivatives were also selectively synthesized by employing NIS and/or Brønsted acid. NIS as an electrophilic reagent could promote these reactions efficiently and rapidly under very mild reaction conditions
Über ein einfaches Verfahren zur Darstellung von Triarylpyryliumsalzen
作者:R. Wizinger、S. Losinger、P. Ulrich
DOI:10.1002/hlca.19560390103
日期:——
Es wird ein einfaches Verfahren zurDarstellungvon 2,4,6-Triarylpyryliumsalzen mitgeteilt. Der Einfluss von Auxochromen, insbesondere von Dimethylaminogruppen, auf die Farbe der Pyryliumsalze und der analogen N- Methyl- pyridiniumsalze wird besprochen. Auxochrome wirken in Verbindung mit dem Triphenylpyryliumion sehr viel stärker bathochrom als in Verbindung mit dem Triphenyl-pyridiniumion. In der
Synthetic studies on a series of functionalized pyrylium salts, 4-chloro- and 4-bromophosphinines
作者:Noriyoshi Nagahora、Hiroshi Tokumaru、Shinpei Ikaga、Takuya Hanada、Kosei Shioji、Kentaro Okuma
DOI:10.1016/j.tet.2018.02.053
日期:2018.4
A series of new pyrylium salts that bear sulfonate and phosphonate groups were obtained from the reactions between 2,6-diphenyl-4H-pyran-4-one, sulfonic anhydride, and chlorophosphates, and analyzed spectroscopically. Furthermore, treatment of 2,6-diphenyl-4H-pyran-4-one with phosphoryl chloride or bromide afforded the corresponding 4-chloro- and 4-bromopyrylium tetrafluoroborates in good yield. Subsequently