2.3- Dihydro-4H-pyrane-4-ones

New possibilities in hetero-Diels-Alder condensation have been opened by the introduction of highly active l-methoxy-3-trimethylsilyloxy-, 4-benzoyIoxy-l-methoxy-3-trimethylsilyloxy-, and 2-acetoxy-l-alkoxy-3-trimethylsilyloxy-l,3-butadienes ( Danishefsky dienes, 5). These compounds readily react under atmospheric pressure, in the presence of Lewis acids, with normal aldehydes (e.g., acetaldehyde, benzaldehyde, furfural) to furnish 2,3-disubstituted or 2,3,5-trisubstituted derivatives of 2,3-dihydro-4H-pyran-4-one 7 capable of readily functionalizing to sugars (Scheme 5) [26]. This approach... 

Adedeji et al. (1993) used a direct thermal desorption technique (220°C) to analyse the volatiles from beans that might cause the thermal degradation and transformation of sugar into common volatile compounds such as 3,5-dimethyl-2,4(3H,5H)-furandione and 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one. This last compound was detected at a high concentration (3880 ppm) in Mexican vanilla, being the third most abundant compound after vanillin and 2-furfural, and far more abundant than vanillic acid, p-hydroxy-benzaldehyde or p-hydroxybenzoic acid. 

Goodwin, T E, Crowder, C M, White, R B, Swanson, J S, Evans, F E, Meyer, W L, Stereoselective addition of organocopper reagents to a novel carhohydrate-derived 2,3-dihydro-4H-pyran-4-one, J. Org. Chem., 48, 376-380, 1983. 

Similarly prepared were 3-acetoxy-2,3-dihydro-4ff-pyran-4-one (2 Rj = H, Rj = OAc) [from l-methoxy-2-acetoxy-3-trimethylsilyloxy-l,3-butadiene (1 Rj = H, R2 = OAc) and paraformaldehyde in 67% yield] and 5-acetoxy-3-benzoyloxy-2,3-dihydro-4H-pyran-4-one (from l-benzoyloxy-2-t-butyldimethylsilyloxy-3-acetoxy-4-methoxy-l,3-butadiene and paraformaldehyde in 75% yield). 

When the reaction was conducted at room temperature under the catalysis of Yb[(-)BNP]3, the asymmetric induction was improved to 73% ee. The effect of the central metal ion of the chiral catalysts on the optical yield of the product, 2-phenyl-2,3-dihydro-4H-pyran-4-one, is shown in Fig. 2. The degree of enanti-oselection is highly sensitive to and dependent on the ionic radius of lanthanide ions [31]. 

CgH,202, Mr 140.18, liquid, [a] +236° (C2H5OH). Sexual attractant of the male butterfly Hepialus cali-fornicus. H. hecta produces the isomeric (R)-6-ethyl-2,3-dihydro-2-methyl-4H-pyran-4-one (CgH,202, Mr 140.18 a). Besides the homologous 2,6-diethyl-2,3-dihydro-4H-pyran-4-one (C9H14O2, Mr 154.21) the... 

Wu and his co-workers reported an experimental and theoretical study on the hydrogen-bond-promoted enantioselective hetero-Diels-Alder reaction (HAD) of Danishefsky s diene 105 with benzaldehyde 106, Scheme 3.37 [52], The reaction was achieved catalytically by a series of a,ct,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) derivatives through hydrogen-bonding activation and afforded 2-phenyl-2, 3-dihydro-4H-pyran-4-one 108 in good enantioselectivity. 

The preparation of branched-chain 4-eno-pyran-2-uloses derived from levoglucosenone is mentioned in Chapter 14. Studies on the addition of methanol to 2-C- and S-C-nitro-a- and P-D-cryt/iro-hex-2-enopyranosides as well as the preparation of C-1 glycosides by the addition of organometallic agents to 2,3-dihydro-4H-pyran-4-ones can be found in Chapter 3. 

Pyran-4-one, 2,2,5-trimethyl-2,3-dihydro-photodimerization, 3, 720 4H-Pyran-4-one, 2,3-dihydro-2,3,5-trimethyl-6-( 1 -methyl-2-oxobutyl)-synthesis, 3, 844 Pyranones alkylation, 2, 56 aromaticity, 3, 632, 633 C NMR, 3, 587, 635 H NMR, 3, 580 cardiac glycosides, 3, 883 chromone synthesis from, 3, 830 colour couplers... 

Hydroxy-6-methyl-5,6-dihydropyran-2-one (597) is brominated by NBS at C-3 (78JHC1153). More than one product is often obtained in this type of reaction, for example from 2,3-dihydro-4//-pyran (593), but in acetic acid this reaction gives 2-acetoxy-3-bromotetrahydropyran (599) (58JOC1128). 2,3-Dihydro-4H-pyran reacts normally with hydroboration reagents to give tetrahydropyran-3-ol in 80% yield (70JOC2282). 

Only two Anobiidae pheromones have been identified thus far. The drugstore beetle, Stegobium panlceum (L.), pheromone was identified as 2,3-dihydro-2,3,5-trimethyl-6-(l-methyl-2-oxo-butyl)-4H-pyran-4-one (XIV) (44) and the cigarette beetle, Lasloderma serrlcorne F., as 4,6-dimethyl-7-hydroxy-nonan-3-one (XV) (45). The similarity of these structures is worth noting. 

Lasius fuliginosus W-HG Trail following antennal responses (3R)-(-)-3,4-Dihydro-8-hydroxy-3-methyliso-coumarin 129 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one 134 [175]... 

The major products formed from hexoses that react in aqueous acidic solution are 5-(hydroxymethyl)-2-furaldehyde, levulinic acid, and polymeric materials. In addition, many minor dehydration products are found. In a study41 of D-fructose, 2-(2-hydroxyacetyl)furan (13), 2-acetyl-3-hydroxyfuran (isomaltol 16), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, and 3,4,5-trihydroxy-3,5-hexadien-2-one (acetylformoin) were identified. Products not formed solely by dehydration mechanisms include acetone,56 formaldehyde, acetalde-... 

Figure 6.6 Structures of 2,3-dihydro-2,3,5-trimethyl-6-(1 -methyl-2 -oxobutyl)-4H-pyran-4-one (stegobinone), pheromone of Stegobium paniceum (L.) (Anobiidae) (Kuwahara et al., 1978) and (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene, pheromone component of Carpophilus hemipterus (L.) (Nitidulidae) (Bartelt et al., 1991). The carbon skeletons are identical, and likely derived through similar pathways (see text).

FIGURE 7.10 Structures of volatile compounds characterized from toasty caramel aroma released in wine from toasted woods during aging. (1) 3,5-dihydroxy-2-methyl-4H-pyran-4-one (2) 3-hydroxy-2-methyl-4H-pyran-4-one (3) 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) (4) 4-hydroxy-2,5-dimethylfuran-3(2H)-one (furaneol) (5) 2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one (dihydromaltol) (6) 2-hydroxy-3-methyl-2-cyclopenten-l-one (or cyclotene) (Cutzach et al., 1997 ) (7) 3-hydroxy-4,5-dymethyl-2(5H)-furanone (Sotolon Camara et al., 2006a,b,c) (8) 2-furanmethanethiol (furfurylthiol Tominaga et al., 2000). 

In studying the degradation of fructosylglycine in unbuffered and buffered aqueous solutions at 90 °C over 7 h, the pH being kept constant at 5, 6, 7, or 8, HMF was detected by Davidek et al.100 only at pH 5, whereas 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one was formed over the whole pH range studied. The phosphate buffer accelerated the formation of the latter compound at pH 5 and 6, but the formation of HMF was practically unaffected, suggesting that phosphate catalyses 2,3-enolisation at lower pH values. 

Soyasaponin ag (= Soyasapogenol 3-0-glycoside 22-O-DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one) ether) (terpene saponin glycoside DDMP ether)... 

Figure 7.1.1. Chromatogram for the pyrotysate ofgtucose obtained by on-line Py-GC/MS. The peak assignments are 1 furan, 2 2-melhylfuran, 3 2,5-dimethylfuran, 4 3-methyl-2-butanone, 5 water, 6 1-hydroxypropanone, 7 hydroxyacetaldehyde, 8 acetic acid, 9 oxopropanoic acid methyl ester, 10 furancarboxaldehyde, 11 1-(2-furanyl)-ethanone, 12 5-methyl-2-furfural, 13 2-hydroxycyclopent-2-en-1-one, 14 2-hydroxy-3-methyl-2-cyclopenten-1-one, 15 2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one, 16 2-methyl-1,3-benzendiol, 17 2,5-dimethyldioxane, 18 2-hydroxy-3-pentanone, 19 5-formyl-2-fufurylmethanoate, 20 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, 21 1,4 3,6-dianhydro-a-D-glucopyranose, 22 5-(hydroxymethyl)-furancarboxaldehyde.

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