Pyrone 2,3-dihydro

Furo[2,3-amino-synthesis, 4, 986 Furo[3,4-d]pyrimidinedione synthesis, 4, 987 Furopyrimidines, 4, 986 Furo[2,3-d]pyrimidines synthesis, 4, 986 Furo[3,2-d]pyrimidines synthesis, 4, 987 Furo[3,2- 6]pyrone synthesis, 4, 994 Furo[3,2-c]pyrone synthesis, 4, 993 Furo[3,2-6]pyrrole, hexahydro-biological activity, 6, 1024 1 H-Furo[3,4-6]pyrrole-2,3-dione, 4,6a-diphenyl-6-(phenylimino)-6,6a-dihydro-synthesis, 6, 1004 Furopyrroles... 

The equilibrium between 2,3-dihydro-4-pyrones and l-penten-3,5-diones is a related process which can be pictured as involving a reaction with a cyclic 6-membered transition state (see Scheme 2). 

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. 

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... 

Propionic acid, 2-iodo-3-nitro-, ethyl ester [Propanoic acid, 2-iodo-3-mtro-, ethyl ester], 65 2//-Pyran, 3,4-dihydro-, 51 2//-PYR AN-2-ONE, 49 2H Pyran 2-one, 5 bromo 5,6-dihydro, 50 27/-PYRAN-2-ONE, 5,6 DIHYDRO-, 49 PYRIDINE, 2,3,4,5 TETRAHYDRO, 118 Pyridines, -substituted, 34 a Pyrone-6-carboxyhc acid [2H Pyran-6-Larboxyhc acid 2-oxo ], 51 Pyrroles, 34... 

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. 

All reactions listed in Tables 5-7 were carried out under a nitrogen atmosphere, but with the rhodium or palladium catalysts no noticeable or only minor reduction in cyclopropane yields was observed when air was present. In contrast, air clearly had a yield-diminishing effect in the CuCl P(0-/-Pr)3-catalyzed reactions, especially with cyclohexene and 3,4-dihydropyran. Cyclohexene was oxidized to 2-cyclohexen-l-one, and 3,4-dihydropyran gave 5,6-dihydro-4-pyrone and 5,6-dihydro-2-pyrone, albeit in yields below 8 % 59). 

The first report of a cycloaddition reaction in the presence of an optically active catalyst13 appeared in 198314a. The dienes 14 add to benzaldehyde in the presence of 1 mol% of the chiral lanthanide NMR shift reagent Eu (hfc)3, i.e. tris[3-(heptafluoropropyl-hydroxymethylene)-(+)-camphorato]-europium(III), to give, after treatment with trifluo-roacetic acid, the dihydro-y-pyrone 15 enriched in the (R)-enantiomer, the degree of... 

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). 

The Deng group identified QN-derived thiourea 121 and QD -derived thiourea 124 to be also efficient promoters of enantio- and diastereoselective Diels-Alder reactions between the 2-pyrone diene 3-hydroxypyran-2-one and the dienophiles fumaronitrile, maleonitrile as well as acrylonitrile, while various C9-hydroxy acylated and alkylated (dihydro)cupreines and (dihydro)cupreidines failed for the same reactions under identical conditions (e.g., 97% yield, 15% ee, 64 36 endoxxo) [289], Catalysts 121 and 124 (5mol% loading), however, produced the corresponding Diels-Alder adducts 1-3 with synthetically useful enantioselectivities (85-... 

Diese Reaktionsart ist bei den Addukten aus Butadien-carbonsaure-Derivaten mit der Carboxylgmppe in 3-Stellung allein verwirklicht dabei entstehen 3-Amino-a-pyrone [58, 70, 72). So geht das N-p-Chlorphenyl-3-methoxycarbonyl-6-phenyl-3.6-dihydro-1.2-oxazin bei der Chromato-graphie an Aluminiumoxid in 3-p-Chloranilino-6-phenyl-a-pyron uber (55), der Mechanismus ist analog dem der Pyrrolbildung. 

The degree of unsaturation of the heterocyclic product depends on the nature of the five-carbon starting material pentane-1,5-diones yield dihydro compounds (151 —> 152) (which are sometimes oxidized in situ) pentane-1,3,5-triones (153) give y-pyrones (154 Z = 0) by dehydration, and y-pyridones (154 Z = NH) by the action of ammonia. 

Two approaches, based on furan, have found wide application in carbohydrate synthesis. Cycloaddition reactions of furan with 2-substituted acrylonitrile or acrolein lead to oxabicycloheptanes which, in tnm, can be transformed to monosaccharides. On the other hand, furfuryl alcohols can be converted—either by the Clauson-Kaas reaction or by mild oxidation—into 5,6-dihydro-4-pyrones, suitable for easy functionalization to sugars. 

The 5,6-dihydro-a-pyrone ring is present in several biologically active molecules697,698. This ring system may be usefully prepared, in a one-pot procedure, via a directed aldol-type condensation followed by cyclization (equation 194)6". The products are usefully functionalized with a carboxylic ester group in the 3-position which allows further synthetic elaboration. 

Cyclocondensation of dioxygenated 1,3-dienes with aldehydes. In the presence of ZnCl2 in benzene or BP3 etherate in ether, this diene 1 undergoes cyclization with a wide variety of aldehydes to afford 2,3-dihydro-y-pyrones (equation I). The products... 

Hovorka SW, Hageman MJ, Schoneich C. Oxidative degradation of a sulfonamide-containing 5,6-dihydro-4-hydroxy-2-pyrone in aqueous/organic cosolvent mixtures. Pharm Res 2002 19 538-545. 

Chemical Name (R-(E))-5,6-Dihydro-4-methoxy-6-styryl-2H-pyran-2-one Common Name Cavain Gonosan Kavain Kava pyrone Kawain Structural Formula ... 

A quantitative relaxation study has also been reported13 for the sugar analog 5-acetoxy-5,6-dihydro-6-(l,2-epoxypropyl)-2-pyrone (23, asperlin ), which... 

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