Pyrane-2,4-diones

H-Pyran-2,6-dicarboxylic acids synthesis, 3, 758 Pyran-2,4-dione, 3,3-dimethyl-photodimerization, 3, 720 reactions... 

H-Pyran-2,4-dione, 3-acetyl-6-methyl-food preservative, 1, 410 Pyran-2,6-dione, tetrahydro-polymers, 1, 313 Pyrandiones synthesis, 3, 793... 

A similar method has been described by Badia and co-workers who used chiral amides derived from pseudoephe-drine.139 Moreover, a zirconium-mediated Claisen-aldol tandem reaction of an a,cr-dialkylated ester with several aldehydes has been reported (Scheme 39).140 After the initial Claisen condensation, zirconium enolate intermediate 92 reacts with various types of aldehydes through aldol-type reaction and subsequent lactonization, providing the corresponding pyran-2,4-diones. 

Benzoic acid and its derivatives are among the most widely used antimicrobial agents these, together with the propionates, sulfur dioxide, nitrates, nitrites and sorbic add, account for the bulk of food preservatives. A number of other compounds find use, however, in various miscellaneous applications, including 3-acetyl-6-methyl-3f/-pyran-2,4-dione (67)... 

A nitrile-stabilized carbanion is also involved in a synthesis of a fused pyranone system (81S225). A range of 2-ureidomethylenecyclohexane-l,3-diones, e.g. (308), react with activated acetonitriles in the presence of a strongly basic catalyst to produce 5-oxo-5,6,7,8-tetrahydrocoumarins (309). Since the substrates are readily available from cyclohexane-1,3-diones by reaction with triethyl orthoformate and a urea, the synthesis is attractive (Scheme 88). Furthermore, it has been applied to a pyran-2,4-dione, whereupon the 2,5-dioxopyrano[4,3-6]pyran (310) is formed. 

The UV spectra of 3-acetylpyran-2,6-diones 219 (R1 = H, Me, R2 = H R1 = Me, R2 = COMe) are comparable to that of the isomeric pyran-2,4-diones 218, except for significant red shift on addition of water to the solution, which indicates the presence of extensively delocalized anions in polar solvents. Schiff bases of 219 (R1 = Me R2 = H) with aniline and / -toluidine exist predominantly in the amino-oxo form in chloroform solution (86JCS(P2)973). 

A similar oxotcchnetium(V) complex of highly distorted octahedral coordination geometry was prepared using the pentadentate ligand N,N -3-azapentane-l,5-diyl-bis(3-(l-iminoethyl)-6-methyl-2H-pyran-2,4-dione) (H3apa). The purple-red. neutral... 

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