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Novel 2-pyrone synthesis via Michael addition of …

21/11/1978 · Preparation of gamma-pyrones from 3-substituted furans

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A two-step synthesis of 6-alkyl-2-pyrones recently ..

4-Bromo-6-methyl-2-pyrone (173) is an attractive class of 2-pyrone family, hosting a broad range of reactions to maximize its synthetic utility. It is easily accessible from bromination of commercially available 4-hyroxy-6-methyl-2-pyrone using PCl3 or TBAB (tetrabutylammonium bromide) via Vilsmeier Haack type reaction []. The 4-carbon center is very reactive towards oxidative addition to Pd(0) species as it is an electron deficient carbon within the 2-pyron e ring and therefore an activated position.

In summary, we present a new method for the synthesis of substituted 2-pyrones

The significance of 2-pyrones and dihydrofurans as units possessing biological activity, selective COX-1 inhibition, and as structural units of bioactive natural and unnatural products, respectively, is noted. Fourteen optimization experiments established the best conditions as shown. Scope for R1 = alkyl, benzyl, aryl, and R2,R3 = substituted pyrrolidinyl, piperidinyl, and one case of dibutyl was established for the 2-pyrone synthesis, while mainly R2,R3 = piperidinyl derivatives for the dihydrofurans were obtained. In the glyoxal study, as expected, EWG = NO2 led to poor yields of product. Experiments were carried out in a flame-dried Schlenk tube under argon atmosphere. Significance of this work would have been increased if further transformation of products and would have been carried out or noted (for example, for , use for Diels–Alder chemistry).

Novel 2-pyrone synthesis via Michael addition of ..

2-pyrone is extremely prevalent in numerous natural products isolated from plants, animals, marine organisms, bacteria, fungi, and insects that exhibit a broad range of biological activities, such as antifungal, antibiotic, cytotoxic, neurotoxic and phytotoxic() []. Moreover, 2-pyrone can serve as a versatile building block for the synthesis of key intermediates in synthetic organic chemistry as well as in medicinal chemistry due to the existence of functional groups, such as conjugated diene and the ester group. Thus, development of a highly efficient synthetic method affording substituted 2-pyrones under mild conditions has been one of considerable attention in organic chemistry.

Reported is a three-component reaction of propargyl alcohols, aldehydes, and amines under copper(I) catalysis to form 3-amino-2-pyrones and 2,5-dihydrofurans. It follows a previous report from the Ma laboratories in which the same components afforded allylic amines ( , , 3884). The difference appears to be that the aldehyde component is ethyl glyoxylate; there is little if any modification of the reaction conditions or the catalyst. Consideration of the readily derived mechanism of the reaction allows formulation of the 2-pyrone as the expected product resulting from mild (silica gel) acidic treatment of isolated intermediate , R = OEt, which in turn results from an allene precursor. A rational consideration that EWG in the aldehyde component would encourage formation of the furan ring was confirmed by using glyoxal and the isolation of dihydrofurans , R = Ph. A reasonable mechanism is given which, although proceeding via isolated , lacks further definition especially in terms of graphical representation of copper involvement. Both processes were tested with at least ten examples each, thus sufficient to justify giving these new processes general status.

addition of mandelic acid enolate to trans ..

A two-step synthesis of 6-alkyl-2-pyrones recently developed by Negishi and co-workers involves Pd-catalyzed alkynylzinc-haloacrylic acid coupling and ZnBr2-catalyzed lactonization () []. Therefore, under this reaction condition, (Z)-5-alkyl-2-en-4-ynoic acids (10) furnishes 6-alkyl-2H-pyran-2-ones (11) in high yields. Although this method provides (Z)-5-alkylidenefuran-2(5H)-ones (12) as minor products, the ratios of pyranone and furanone are often very high. In contrast, lactonization of 10 catalyzed by Ag2CO3 provides (Z)-5-alkylidenefuran-2(5H)-ones (12) selectively in >90% yields along with minor amounts of 11.

Hiroshi Yamaoka,; Ikuhiro Mishima,; Mitsuko Miyamoto,; Terukiyo Hanafusa. The Acid-catalyzed Reaction of the 2-Oxabicyclo[4.1.0]hept-3-en-5-one System: Isomerization from Homo-4-pyrones into 2-Furylacetone Derivatives. Bulletin of the Chemical Society of Japan. 1980, 53 (2), 469-477. A. Ya. Medne,;N. O. Saldabol. Synthesis and transformations of furan derivatives. Chemistry of Heterocyclic Compounds. 1966, 1 (4), 423-425.

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  • A synthesis of substituted 2-pyrones by carbonylative ..

    Cyclisation to furan 4a

  • Synthesis of Isocoumarins and α-Pyrones via Tandem …

    The present review summarizes the recent progresses in the synthesis of 2-pyrones and the ..

  • Recent Advances in the Synthesis of 2-Pyrones

    Synthesis of isocoumarins and alpha-pyrones via tandem Stille reaction ..

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Novel 2-Pyrone Synthesis via Michael Addition of …

The synthesis of 4,6-disubstituted and 3,4,6-trisubstituted 2-pyrones from (phenylthio)acetic acids and α,β-unsaturated trifluoromethyl ketones was achieved via an one-pot isothiourea-mediated Michael addition/lactonization/thiol elimination cascade sequence () [].

Novel 2-Pyrone Synthesis via Michael Addition of ..

To overcome the selectivity problem existing in the iodolactonization reaction, Cy2NH·HX catalytic system was developed by Li and co-workers () []. Thus, 5-bromo-2-pyrone was synthesized from the cyclization reaction of (Z)-pent-2-en-4-ynoate with CuBr2. When 0.1 equivalent of Cy2NH·HCl was added in combination with two equivalents of CuBr2, cyclization of (Z)-ethyl 5-phenylpent-2-en-4-ynoate underwent a smooth conversion to the corresponding product in 47% in 6 h. This reaction extends to a variety of o-(alk-1-ynyl)benzoates to provide the corresponding 4-haloisocoumarins in moderate to excellent yields.

to trans-1,2-diaroylethenes, cyclisation to a furan ..

Usachev and co-workers developed a convenient synthesis of a series of 2-pyrones with a CF3 group at the 6-position and aryl group at position 4, from readily available aryl-4,4,4-trifluorobutane-1,3-diones (125), PCl5, and sodium diethyl malonate (126) () [].

Synthesis of 3-Aryl-2-pyrones by Palladium ..

Later, Baran and co-workers applied this method to the total synthesis of (±)-haouamine A (137) on the premise that a cyclohexadiene from the pyrone-alkyne Diels-Alder reaction can serve as a viable precursor since it can release CO2 to undergo subsequent aromatization () [].

Find Ethyl 3-(furan-2-yl)propionate available at Sigma-Aldrich.

Due to the outstanding stereochemical outcome in the Diels-Alder cycloadditions, substituted 2-pyrones have been extensively used as key intermediates in the synthesis of complex natural products. Especially, brominated 2-pyrones are attractive ambident dienes as they can react with both electron poor and rich dienophiles via normal- and inverse-electron-demand Diels-Alder cycloadditions with good stereocontrol. The dual reactivity of brominated 2-pyrones is resulted from the fact that the bromine atom at 3- or 5-position on the 2-pyrone ring can either withdraw or donate electron density to the diene moiety of the 2-pyrone ring. However, despite the versatility and usefulness of brominated 2-pyrones, their synthetic application has been hampered by the limited accessibility.

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