Pyrone derivates

Synthesis, structure, and transformations of a-pyrone derivatives, viz., xanthy-rones, glaucyrones, and chelated magnesium enolates 98T8243. 

Marko I. E., Evans G. R., Seres P., Chelle L, Janousek Z. Catalytic, Enantiose-lective, Inverse Electron-Demand Diels-Alder Reactions of 2-Pyrone Derivatives... 

Arylmethylene-2-thioxo-4-thiazolidinones (34) react with phosphonium ylides to give dihydrofuro[2,3-rl]thiazol-2(3 -ones (35) in refluxing ethyl acetate, while performing the reaction in refluxing toluene led to the pyrone derivative (36) both of these products result from an initial 1,4-addition to the exocyclic double bond <95T11411>. 

Pyridoxal 157,158,253 Pyridoxamine 253 Pyridoxine 253 Pyrimidines 266,438, 439 Pyrocatechol see 1,2-Dihydroxybenzene I ocatecholsulfophthalein 398 I ocatechol violet reagent 398 Pyrolysis of organic compounds 92, 96 a,y-Pyrone derivatives 288 Pyrrole alkaloids 66 Pyrrole derivatives 266, 269, 270 Pyruvic acid 426... 

Synthesis with sacrificial electrodes is employed as a direct method in several other preparations of organometallic compounds and complexes. 3-Hydroxy-2-methyl-4-pyrone derivatives of Sn 1 (and of Zn, Cu, In and Cd as well) were prepared using the metal as an anode. The low oxidation state Sn(II) compound is obtained by direct electrolysis134. 

In spite of these first successful results, so far Stille cross-couplings have rarely reported employing functionalized stannylated allenes such as easily available donor-substituted allene 80a or allenyl esters such as 81 (Scheme 14.19) [19, 41, 42]. A single palladium-catalyzed annulation reaction with 80b as precursor leading to an a-pyrone derivative was reported [43],... 

Kraut, L. et al., Carboxylated a-pyrone derivatives and flavonoids from the liverwort Dumortiera hirsuta. Phytochemistry, 42, 1693, 1996. 

It has been found that l,3-di(ethoxycarbonyl)allene reacts readily with such heterocyclic dienes as furan, pyrrole, and pyrone derivatives. The furan adduct 383, obtained in 87% yield, was hydroxylated, and after acetonation, was cleaved251 with ozone, to afford intermediate 384. An approach to the conversion of 384 into C-glycosyl compounds by hydride-promoted scission of the C-5-C-6 bond was disclosed.255... 

The cumulation reactions, which start from carboxylic acids and esters usually lead to the formation of pyrone derivatives. Methyl (Z)-3-iodoacrylate and 3-hexyne gave, for example, 5,6-diethyl-2-pyrone in acceptable yield (4.38.). Inclusion of the acrylate into a six membered ring starting from ethyl 2-bromocyclohexen-l-carboxylate, led to a condensed ring system, giving a partially reduced isocoumarin derivative.50... 

The analogous open chain carboxylic acid, Z-non-2-en-4-ynoic acid, when treated with 4-iodoanisole in the presence of a palladium-triphenylphosphine catalyst and potassium carbonate gave a mixture of three products, two of which were isolated (4.41.) z) the pyrone derivative arising from the attack of the anisylpalladium complex at the 4-position, followed by ring closure //) the furane derivative (major product) arising from the... 

The synthesis of pyrone derivatives attracted attention due to their synthetic potential. In an illustrative example Cho and co-workers studied the Suzuki-coupling of 3,5-dibromo-2-pyrone with arylboronic acids (8.9.). Under regular conditions the aryl group is introduced selectively into the more electron deficient 3-position, while in the presence of an equimolar amount of copper(I) iodide the coupling is diverted selectively into the 5-position (N.B. drop of the reaction temperature from 50 °C to ambient temperature negated the effect of copper and led to 3-arylation). The way copper effects the coupling is still unclear, but it was successfully used in the preparation of a range of 5-aryl-2-pyrons.17... 

Schulte and coworkers (62AP801) have prepared a number of 3-propargyl-4-hydroxy-2-pyrone derivatives (210) by condensation of /3-dicarbonyl compounds (208) with propargyl-malonyl chloride (209). On heating (210) with zinc carbonate, ring closure took place to give the corresponding furo[3,2-c]pyrone derivatives (211 Scheme 40). 

BSB451). Metalated enamines (in the a-methyl group) easily react with aldehydes, and the new enamines thus formed undergo an intramolecular cyclization giving 2-pyrone derivatives (84T733) (Scheme 41). 

A different route to pyrones is the preparative electrochemical oxidation of enamines in acetonitrile in the presence of tetraethylammonium perchlorate (88MI2) (Scheme 46). The synthesis of 2-pyrone derivatives has been carried out by reaction of /3-dicarbonyl compounds with methyl-a-benzoylamino-/3-dimethylaminoacrylate (96JHC751). Thiapyran derivatives can be obtained by interaction of enamines based on (/3-amino-a-cyanoacryloylmethyl)pyridinium chloride derivatives with carbon disulfide (95M711).The synthesis of pyridine derivatives based on analogous enamines has been described as well (95M711). 

The photorearrangement of certain epoxycyclopentenones takes a different course to yield 2-pyrone derivatives one example is the conversion of 3,4-diphenyl-4,5-epoxycyclopent-2-en-l-one (20) into 4,5-diphenyl-2-pyrone (21), and this can be rationalized by assuming cleavage of the oxirane to give the diradical (22) or its equivalent,... 

Kato et al,94 reported that 2-amino-6-methylpyridine and diketene did not yield 4-oxo-4/f-pyrido[l,2-a]pyrimidines but instead yielded 2-acetyl-acetamido-6-methylpyridine and pyridone or pyrone derivatives. 2-Methyl-4-oxo-4H-pyrido[l,2-a]pyrimidine (47) and its 8-methyl derivative have also been prepared from 2-aminopyridine and 2-amino-4-methylpyridine with N,N-dimethyl-3-aminocrotonamide95 or with acetoacetamide45 in yields of 5 and 39°,. respectively. 

PfUhaleins or pyronine or pyrone derivatives, usually red or violet, and related to the preceding group. 

The intramolecular thermal [5+2] cycloaddition of 3-alkoxy-4-pyrones with sulfur- (e.g., 416) or silicon- (e.g., 419) tethered alkenes has been shown to occur with complete regio- and stereochemical control to give adducts 417 and 421, respectively. The adducts can be converted by reduction and oxidation, respectively, to the bicyclic products 418 and 421 (Scheme 69) <1993JOC5585>. It should be noted that this thermal [5+2] cycloaddition has not been realized in a bimolecular mode <1977JOC3976>. This methodology serves as an alternative to the reaction of electron-deficient alkenes with pyrone-derived 4-methoxy-3-oxidopyrylium ylides <1992TL2115>. 

The synthesis of a spiroketal fragment 450 of spongistatin 1 has been accomplished utilizing the addition of a metalated pyrone derived from 448 to propionaldehyde to give adduct 449 followed by acid-catalyzed spirocycliza-tion (Scheme 79) <20000L957>. 

The Kava plant, Piper methysticum, has been used by Pacific Island societies for several thousand years to prepare an intoxicating ceremonial beverage renowned for its relaxing effects and purported health benefits <1997MI84>. The psychoactive principles extracted from the Kava root are a family of 15 ct-pyrone derivatives known as the kavalac-tones. The more prevalent of these include (+)-kavain 61, (+)-methysticin 62, yangonin 63, and their more saturated derivatives 64, 65, and 66, respectively. 

Figure 42. Catalytic, asymmetric Diels-Alder reaction of 2-pyrone derivatives.

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