37786-68-8Relevant articles and documents
Rhodium-Catalyzed Regioselective Domino Azlactone–Alkyne Coupling/Aza-Cope Rearrangement: Facile Access to 2-Allyl-3-oxazolin-5-ones and Trisubstituted Pyridines
Kuang, Jinqiang,Parveen, Shaista,Breit, Bernhard
, p. 8422 - 8425 (2017)
Rhodium-catalyzed regioselective addition of azlactones to internal alkynes combined with aza-Cope rearrangement provides efficient atom economic access to 2-allyl-3-oxazolin-5-one derivatives. Extension to a triple domino process, in which the above process is combined with in situ azlactone formation starting from amino acids renders this process even more attractive. Subsequent thermolysis of the 2-allyl-3-oxazolines enabled the de novo synthesis of trisubstituted pyridines.
Transition-metal-free synthesis of substituted pyridines via ring expansion of 2-allyl-2H-azirines
Jiang, Yaojia,Park, Cheol-Min,Loh, Teck-Peng
, p. 3432 - 3435 (2014/07/21)
A new strategy to open the 2-allyl-2H-azirines by 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) promotion in metal-free conditions affording 1-azatrienes that in situ electrocyclize to the pyridines in good to excellent yields is reported. The reaction displays a broad substrate scope and good tolerance to a variety of substituents including aryl, alkyl, and heterocyclic groups. In addition, one-pot synthesis of pyridines from oximes via in situ formation of 2H-azirines was achieved.
A modular synthesis of functionalized pyridines through lewis-acid-mediated and microwave-assisted cycloadditions between azapyrylium intermediates and alkynes
Linder, Igor,Gerhard, Markus,Schefzig, Luise,Andrae, Michal,Bentz, Christoph,Reissig, Hans-Ulrich,Zimmer, Reinhold
supporting information; experimental part, p. 6070 - 6077 (2011/12/02)
In this report we describe the synthesis of differentially functionalized pyridine derivatives 3 and the related 3-bromo-substituted pyridines 11. Dissociation of 6H-1,2-oxazine precursors (1a, 1b, 5, 6, or 12) in situ, mediated by boron trifluoride-diethyl ether, generates the azapyrylium intermediates A, which undergo hetero-Diels-Alder reactions with various mono- and disubstituted alkynes 2. In general, these pyridine syntheses proceeded with high efficiencies and were very flexible with respect to all positions in the pyridine cores. For the 3-phenyl-substituted pyridine derivatives 3a-3j and 11a-11f the best results were obtained by a new microwave-assisted protocol, which is clearly superior to the previously used conventional procedure at low temperature in dichloromethane. Furthermore, 3-(trifluoromethyl)- and 3-acryloyl-substituted 6H-1,2-oxazines reacted cleanly under microwave irradiation conditions to furnish the expected pyridine derivatives 3k and 3l in respectable yields. The 3-bromo-substituted pyridines 11 were further functionalized through palladium-catalyzed couplings such as Suzuki or Sonogashira reactions, which led smoothly to tri- or tetrasubstituted pyridine derivatives such as 19-21 and 23. Reductive debromination of 11e afforded the pyridine 17 in excellent yield, whereas oxidation of the pyridinyl thioether 3g with oxone led to the corresponding sulfoxide 24. Our method thus establishes a new and versatile approach to highly substituted pyridine derivatives. A simple method for the modular synthesis of substituted pyridines is disclosed. Microwave-assisted reactions between azapyrylium intermediates (generated in situ) and alkynes afforded the corresponding pyridine derivatives in good to excellent yields. The functional group tolerance in this process is very good and allows a variety of subsequent reactions.
