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Synthesis of 2-pyrones

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An electrophilic pyrone derivative, which can be readily prepared on a multigram scale, undergoes metal-catalyzed cross-coupling reactions with a variety of nucleophiles to yield 3-substituted-2-pyrones.
F. Frébault, M. T. Oliveira, E. Wöstefeld, Nuno Maulide, J. Org. Chem., 2010, 75, 762-7695.

A palladium-catalyzed cross-coupling reaction of cyclic vinyldiazo ester with aryl iodides provides various 3-aryl-2-pyrones in good yields with high functional group tolerance. The resulting 3-aryl-2-pyrones can be used as diene components in Diels-Alder reactions.
J. Huang, L. Li, H. Chen, T. Xiao, Y. He, L. Zhou, J. Org. Chem., 2017, 82, 9204-9209.

Sequential alkyne activation of terminal alkynes and propiolic acids by gold(I) catalysts yields α-pyrones in good yields. Novel cascade reactions involving propiolic acids are reported that give rise to α-pyrones with different substitution patterns.
T. Luo, M. Dai, S.-L. Zheng, S. L. Schreiber, Org. Lett., 2011, 13, 2834-2836.

A gold(I)-catalyzed rearrangement of β-alkynylpropiolactones enables a straightforward synthesis of substituted α-pyrones in good yields.
T. Dombray, A. Blanc, J.-M. Weibel, P. Pale, Org. Lett., 2010, 12, 5362-5365.

An efficient synthesis of 6-substituted 3-(alkoxycarbonyl)-5-aryl-α-pyrones consists of an addition-elimination reaction between benzyl ketone derivatives and dimethyl methoxymethylenemalonate, and an acid-catalyzed condensation reaction. The synthesis is applicable to various multiubstituted α-pyrones in very good yields.
T. Miura, S. Fujioka, N. Takemura, H. Iwasaki, M. Ozeki, N. Kojima, M. Yamashita, Synthesis, 2014, 46, 496-502.

A ruthenium-catalyzed regioselective intermolecular multistep homo- and heterodimerization of substituted propiolates provides α-pyrone-5-carboxylates and α-pyrone-6-carboxylates. The proposed mechanism is strongly supported by experimental evidence.
R. Manikandan, M. Jeganmohan, Org. Lett., 2014, 16, 652-655.

Addition of a catalytic amount of Cy2NH·HX improves the rate and yields for cyclization reactions of o-(alkynyl)benzoates in the presence of a stoichiometric amount of copper(II)halide to give 4-haloisocoumarins. Under the standard reaction conditions, various 4-haloisocoumarins are provided in good yield.
Y. Liang, Y.-X. Xie, J.-H. Li, Synthesis, 2007, 400-406.