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2-Pyrones, 5,6-dihydro- from

A synthesis of 2-alkyl-2,3-dihydro-y-pyrones (187) from methoxybutenyne and aldehydes has been described (83TL4551). The condensation of lithiomethoxy-butenyne (184) with aldehydes at -78°C leads to the secondary alcohols 185, which form the dihydropyrones 187 via hydration of the acetylenic bond and hydrolysis of the methoxyethenyl group to the ketoenol 186 (0°C, p-TSA, THF, H2O or 30% HCIO4, 20 min) folowed by intramolecular cycloaddition. [Pg.206]

There have been very few examples of 5,6-dihydro-a-pyrones isolated from the marine environment. In 1992, Hamada et al. obtained lobatrienolide (18) from an Okinawan soft coral Sinularia flexibilis (25). The structure of lobatrienolide was established by spectral techniques and confirmed by photo-oxidation of lobatriene (19), isolated from the same soft coral collection, to (18). The structure of (19) was proved as follows Scheme 1). Lithium-ethylamine reduction of (19) produced the diol (20) which on ozonolysis, MCPBA oxidation to the acetate (21) and hydrolysis gave the alcohol (22). The 5-stereochemistry of the alcoholic group in (22) was determined by the modified Mosher method 24), which together with NMR correlations in lobatriene, afforded the complete stereochemistry of (19) and hence also that of lobatrienolide... [Pg.184]

The trihydroxyheneicosyl-5,6-dihydro-a-pyrone (47) from Eupator-ium pilosum has been synthesised from (—)-malic acid (59). Syntheses... [Pg.189]

Drewes, S.E., B.M. Sehlapelo, M.M. Horn, R. Scott-Shaw, and P. Sandor 5,6-Dihydro-a-pyrones and Two Bicyclic Tetrahydro-a-pyrone Derivatives from Crypto-carya latifolia. Phytochem., 38, 1427 (1995). [Pg.205]

Dihydro-2f/-pyran-2-one has been prepared by reductive cycliza-tion of 5-hydroxy-2-pentynoic acid [2-Pentynoic acid, 5-hydroxy-], which is obtained in two steps from acetylene [Ethyne] and ethylene oxide [Oxirane] 3 and by the reaction of dihydropyran [277-Pyran, 3,4-dihydro-] with singlet oxygen [Oxygen, singlet].4,5 2ff-Pyran-2-one has been prepared by pyrolysis of heavy metal salts of coumalic acid [2//-Pyran-5-carboxylic acid, 2-oxo-],8 by pyrolysis of a-pyrone-6-carboxylic acid [211 - Pyran-6-carboxyl ic acid, 2-oxo-] over copper,7 and by pyrolysis of coumalic acid over copper (66-70% yield).8... [Pg.51]

Lia DJ, Mariko K, Hiromitsu T, Sjamsul AA, Norio A. A 6-substituted-5,6-dihydro-2-pyrone from Cryptocarya strictifolia. Phytochemistry 2000 54 989-993. [Pg.164]

It has been shown22 that the reaction of the diene 4 with aldehydes RCHO in the presence of a catalyst prepared from (R)-BHMOL (33) and Ti(OPr-i)3, which affords the dihydro-y-pyrones 35 in good yields and high ee, proceeds by a two-step sequence via the open-chain adducts 34, which cyclize to the products on treatment with trifluoroacetic acid (equation 20). [Pg.489]

The HDA reaction allows for rapid access to chiral six-membered heterocyclic structures that serve as valuable intermediates in organic synthesis. The first highly enantioselective HDA reaction promoted by a chiral hydrogen bond donor was reported from the Rawal laboratory. While investigating the cycloaddition reactions of amino-siloxy diene 115, it was observed that this diene was exceptionally reactive to heterodienophiles, and underwent HDA reactions with various aldehydes at room temperature, even in the absence of any added catalyst (Scheme 6.14). Subsequent treatment of the intermediate cycloadducts (116) with acetyl chloride afforded the corresponding dihydro-4-pyrones (117) in good overall yields [101]. Further studies of this reaction revealed a pronounced solvent effect,... [Pg.235]

Dimethoxyoxetanes.1 In the presence of ZnCl2, this ketal reacts with 0-hydroxy aldehydes to give 2,2-dimethoxyoxetanes, which can be converted into 4-hydroxy-3-methyl-8-lactones and 5,6-dihydro-2-pyrones. In one case, an optically active lactone was obtained in 80% ee from an optically active y-hydroxy aldehyde. [Pg.139]

A dihydro-derivative (4) of strobiline (M+ 193) was also obtained. In the mass spectrometer, the pyrrolidine ring is opened to give fragments of m/z 165 and 164 (base peak), followed by a retro-Diels-Alder reaction to give fragments of m/z 137 and 136, respectively. The location of the two additional hydrogen atoms was deduced from the relative u.v. extinctions of (3) and (4), which is consistent with the dihydro-y-pyrone skeleton in the latter compound. This was confirmed by 3H n.m.r. spectra that showed no vinylic protons. [Pg.45]

The most common method for the preparation of pyrazoles from other heterocycles is from pyranone-type compounds. Condensation of 2,3-dihydro /7-pyran -ones 787 with various aryl hydrazines in the presence of montmorillonite KSF clay under mild conditions proceeded rapidly to afford enantiomerically pure 5-substituted pyrazoles 788 (Equation 172) <2004TL6033>. Comparable results were obtained when arylhydrazines were reacted with 2-formyl glycals under microwave irradiation <2004TL8587>. Phenylhydrazine and hydrazine were reacted with 3-acetyl-4-hydroxy-6-methyl-2/7-pyran-2-one to afford 4-acetoacetyl-3-methylpyrazolin-5-ones, which were employed in the synthesis of bipyrazoles and pyrazoloisoxazoles <1999JHC1291>. Reaction of 3,3-dialkyl-6-(trifluoromethyl)-2,3-dihy-dro -pyrones with hydrazine hydrate afforded 3-(trifluoromethyl)-5-substituted-pyrazoles <1998RCB1365>. [Pg.104]

The key step in the preparation of 5,6-dihydro-5-pyrones with an incorporated 1,3-polyol system (an example, compound 105 possessing inhibitory activity against C. cucumerinum is shown in Scheme 45) consisted of formation of a 2,3-unsaturated furanose derivative 104, which was prepared from 103. Abstraction of an acidic proton from the C-2 induced 8-elimi-nation, providing the desired target 104 [94]. [Pg.369]

The total stereochemical elucidation of the structure of a cytotoxic 6-tetraacetyl-oxyheptenyl-5,6-dihydro-a-pyrone from Hyptis spicigera has been carried out by Pereda-Miranda and co-workers with the use of molecular mechanics and /hh couplings analysis. [Pg.164]

Rotenone 30, the toxic principle from the roots of derris elliptica, is a natural insecticide. Its structure shows an unique combination of benzannelated dihydropyran, dihydro-4-pyrone and dihydrofuran ring systems. [Pg.266]

Acid-catalysed cyclization of the alcohol 581 yields the dihydro-y-pyrone 582, which is converted into the benzene derivatives 586 by sequential treatment with trimethylsilyl chloride and acetylenes 584 (R = H, Me or C02Me R = Bz or C02Me). The process involves formation of the pyran 583, Diels-Alder addition to the alkynes and extrusion of acetone from the adducts 585. ... [Pg.353]

C H 804, Mr 214.26, mp. 88-89 C, [a]g -86° (CH3OHX A dihydro-a-pyrone from the phytopatho-genic fungus Pestalotia cryptomeriaecola with synergistic activity to the gibberellins. P. stimulates plant growth (see plant growth substances). [Pg.477]


See other pages where 2-Pyrones, 5,6-dihydro- from is mentioned: [Pg.509]    [Pg.534]    [Pg.745]    [Pg.746]    [Pg.148]    [Pg.70]    [Pg.244]    [Pg.83]    [Pg.233]    [Pg.812]    [Pg.325]    [Pg.46]    [Pg.420]    [Pg.34]    [Pg.22]    [Pg.334]    [Pg.93]    [Pg.97]    [Pg.277]    [Pg.348]    [Pg.65]    [Pg.73]    [Pg.833]    [Pg.964]    [Pg.382]    [Pg.394]    [Pg.286]    [Pg.288]    [Pg.623]   


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5,6-Dihydro-2-pyrones

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