Methoxy- -pyron

The puzzling discovery of Collie and Tickle in 1899 that 2,6-dimethyl-4-pyrone (8) affords crystalline salts (9) with acids, which were the first monocyclic pj rylinm salts to be isolated, was interpreted by a formula (21) with tetracovalent oxygen.An active period of research followed. The methosulfate or methiodide of 2,6-dimethylpyrone was converted by ammonia into 4-methoxy-2,6-lutidine, therefore, the exocyclic oxygen of the pyrone must be involved in the salt formation. Thus, formula 21 was disproved and formula 22 was demonstrated for these salts. 

NMR spectra were measured. As RuCl(H20)(csb)2/02/Me2CHCH0/CH2Cl2/4°C it asymmetrically epoxidised styrene and substituted styrenes with e.e. of up to 30% [798]. Complexes with (csb =lR,2R(-)l,2-diaminocyclohexane with 3-acetyl-4-hydroxy-6-methyl-2-pyrone and salicylaldehyde, 5-chloro-5-methoxy, 5-methoxy and 5-nitrosalicyladehyde) asymmetrically epoxidised styrene as RuCKH O) (csb )2/PhIO/CH3CN [799]. 

Dimethyl-4-pyrone (322) was reported to react with dimethyl sulfate at 50°C to provide up to 85% of syrupy 2,6-dimethyl-4-methoxy-2//-pyran (323),318,319 but proof for structure 323 is lacking. 

Past methods used to synthesize 7-pyrones consist of the acylation of methoxy-butyne9 or 4-methoxy-3-buten-2-one10 followed by acid-catalyzed hydrolysis and cyclization. Addition of ketenes to siloxydienes followed by acid-catalyzed elimination has also been employed.11 The present method is superior to these procedures because of the greater diversity of substituted 7-pyrones that can be constructed, and because of the fact that the previous methods demand the use of strong base and low temperatures that make them less suited for scale up. 

Halogen atoms in pyrones and pyridones e.g. 902) are unreactive toward SAE nucleophilic displacement. 3-Halopyridines are less reactive than the a- and 7-isomers but distinctly more reactive than unactivated phenyl halides. Thus, a bromine atom in the 3-position of pyridine or quinoline can be replaced by methoxy (NaOMe-MeOH, 150°C), amino (NH3-H20-CuS04, 160°C) or cyano (CuCN, 165°C). 5-Halogens in pyrimidines are also relatively unreactive. 

A novel route to anthracyclinones is based on the chemistry of quinone-isobenzofuran adducts (77TL3537). The 3-methoxybenzyne-furan adduct (1) was reacted with a-pyrone to give a mixture of lactones (2). Thermolysis of this intermediate in the presence of quinone (3) gave in 93% yield the tetracyclic adduct (4) as a stereoisomeric mixture. Aromatization with sodium acetate in acetic acid gave quinone (5) which was subjected to reduction, C-ring oxidation and mild acid hydrolysis to afford a mixture of ( )-7-deoxydaunomycinone (6) and its 1-methoxy regioisomer (Scheme 1). 

This cycloaddition can be used for two approaches to tropones. One involves cycloaddition of 1 to methyl 5-methoxy-2,4-pentadienoate, as outlined in equation (I). The other is a pressure-promoted cycloaddition of 1 with a-pyrone, outlined... 

The method is an adaptation of the procedure of Light and Hauser.2 2-( -Methoxyphenyl) -6-phenyl-4-pyrone has been prepared in 50% yield by a Claisen-type acylation of -methoxy-acetophenone with ethyl phenylpropiolate accompanied by cyclization.3... 

Keywords 4-methoxy-6-methyl-2-pyrone, maleinimide, [2+2]photocycload-dition, cyclobutane... 

Carbene complexes of Fe and Co carbonyls are also prepared. Unlike the Cr carbene complexes, no cyclopropanation of alkenes occurs with these carbene complexes. Furans are formed by the reaction of alkynes involving rearrangement of methoxy group. The 2-aminofuran 323 is formed by the reaction of the dimethylaminocarbene complex 319 of Fe carbonyl, via rearrangement of the amino group. Under CO pressure, pyrone 324 is the main product [97]. In these reactions, the... 

Methyl-l-penten-3-one-l-ol 1 and glacial acetic acid in benzene was added to pyrrolidine to give 2-methyl-l-pen ten-1-[N-pyrrolidinyl]-3-one 2. Compound 2 when treated with oxalyl chloride and methanol was added, 3,5-dimethyl-2-methoxycarbonyl-4-pyrone 3 was produced. Treatment of compound 3 with sodium borohydride in methanol gives 3,5-dimethyl-2-hydroxymethyl-4-pyrone 4. Compound 4 was converted to 3,5-dimethyl-2-hydroxymethyl-4-pyridone 5 by heating compound 4 with aqueous ammonia in a sealed flask. Compound 5 was converted to 4-chloro-2-chloromethyl-3,5-dimethyl pyridine 6 by treatment with phosphorous oxychloride. Treatment of compound 6 with 5-methoxy-2-mer-captobenzimidazole in tetrahydrofuran gave 2-[2-(4-chloro-3,5-dimethyl pyridinyl)methylthio]-5-methoxy benzimidazole 7. When compound 7 was treated with potassium hydroxide in dimethyl sulfoxide containing methanol, 2-[2-(3,5-dimethyl-4-methoxypyridinyl)methylthio]-5-methoxy... 

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 ... 

In the total synthesis of nalanthalide, the crucial coupling of the 7-pyrone moiety with the diterpenoid core was achieved by lithium halogen exchange of 3-bromo-2-methoxy-5,6-dimethyl-4/7-pyran-4-one 353 and addition of the resulting 3-lithio-7-pyrone 354 to aldehyde 355 to produce 356 in an impressive 87% yield (Scheme 53) <2005OL3745, 2006TL3251>. 

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>. 

Recently, the reaction of masked ortho-benzoquinone [92] with C60 was tested [93]. The [4+2] cycloaddition reaction of such electron-deficient dienes with fullerenes resulted in the formation of highly functionalized bicyclo [2.2.2] octenone-fused fullerenes. The reactants were generated in situ by the oxidation of the readily available 2-methoxy phenols with hypervalent iodine agents. For the several different masked ortho-benzoquinones that were tested, it was found that the yield of the cycloadducts depends on the nature of the starting materials and the reaction conditions. Other Diels-Alder reactions of such electron-deficient dienes with electron-poor fullerenes involved tropones [94], 1,3-butadienes substituted with electron-withdrawing groups [95], and 2-pyrone [96]. 

PENTANETRIONE, 46, 57 cyclization by acid to 2-(/>-methoxy-phenyl)-6-phenyl-4-pyrone, 46, 61... 

CpFe(CO)2(pyrone)]+, pyrone = 4-methoxy-6-methyl-2-pyrone and 3-bromo-4-methoxy-6-methyl-2-pyrone were examined as potential CO releasing molecules but failed to release [195]. 

Two compounds, [CpMo(CO)3(pyrone)]+, pyrone = 4-methoxy-6-methyl-2-pyrone, 42, and 3-bromo-4-methoxy-6-methyl-2-pyrone, 43, were examined as potential CO releasing molecules. Both release CO to myoglobin. [CpMo(CO)3(3-bromo-4-meth-oxy-6-methyl-2-pyrone)]+, 43, which showed the faster CO release also showed good cell viability, cytotoxicity and inhibition of nitrite production using murine... 

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