4 H-Pyrans

H- Pyran-4-one, 3,5-diacetyl-2,6-dimethyl-dipole moment, 3, 626 (37JCS1088) 4H-Pyran-4-one, 2-dichloromethyl- C NMR, 3, 588 (82S500)... 

When chlorinated and dehalogenated in the presence of a base, dimethyl iV-acetylstizobolate, a derivative of the nonproteinogenic stizolobic acid, afforded a derivative of the pyrrolo[3,4-h]pyran system 73 (86LA1968). 

Thus, the potential role of DMHF as a flavor impact compound and as an intermediate to form additional flavor compounds in heat-abused citrus products should be carefully considered. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4-H-pyran-4-one was also isolated from dehydrated orange juice (37) and is known as a novel nonenzymic browning reaction product. This pyranone has a high threshold value, over 200 ppm (38), and appears to possess negligible odor character. 

The compound responsible for OZ 2 has a very intense sweet vanilla odor, but it is co-eluted with guaiacol on Carbowax 20M, which prevents it from being easily detected. Pre-fractionation on silica gel, combined with mass spectrometry and infra-red spectroscopy, identified the molecule responsible 2,3-dihyciro-5-hydroxy-2-methyl-4(H)-pyran-4-one (5), or DHM. 

Figure 7.2.1. Cellulose pyrolysate obtained at 59CP C and trimethylsilylated. The separation was done on a methyl silicone with 5% phenyl silicone type column. 1 1,2-dihydroxyethane, 2 2-hydroxypropionic (lactic) acid, 3 hydroxy acetic (glycolic) acid, 4 turanmethanol, 5 peak from silylation reagents, 6 1,3-dihydroxypropanone, 7 1,4-dioxane-2,5-diol, 8 1,3-dioxolane-4,5-diol, 9 1,3-dihydroxybenzene, 10 2-methyl-1,4-dioxane-2,5-diol, 11 1,4-dihydroxybenzene, 12 3-hydroxy-2-(hydroxymethyl)-2-cyclopenten-1-one, 13 2-hydroxy-5-(hydroxymethyl)-4(H)-pyran-4-one, 14 1,2,3-trihydroxybenzene, 15 internal standard, 16 an anhydrosugar, 17 levoglucosan (1,6-anhydro-p-D-glucopyranose), 18 a monosaccharide, 19 an anhydrosugar, 20 an anhydrosugar, 21 1.6-anhydro-P-D-glucofuranose .

Smith PW, Sollis SL, Howes PD, Cherry PC, Cobley KN, Taylor H, Whittington HR, Bethell RC, Taylor N, Varghese JN, Colman PM, Singh O, Slkarzynski T, Cleasby A, Wonacott AJ. Novel inhibitors of sialidases related to GG167. Structure-Activity, crystallography, and molecular dynamics studies with 4-H-pyran-2-carboxylic acid 6-carbo-xamides. Biorg Med Chem Lett 1996 6 2931-2936. 

A 2,4,6-trisubstituted (2H or 4 H) pyran (38, R = R =Ph) was reported to result in low yield by catalytic reduction of 2,4,6-triphenyl-pyrylium salts by oxidation or by treatment with concentrated sulfuric acid it regenerated the triphenylpyrylium cation. There was no subsequent confirmation of this reaction. The reduction of pyrylium salts with sodium borohydride affords 1,5-diones by way of 4H-pyrans and 2,4-dien-l-ones by way of 2H-pyrans. ... 

H-Pyran, 2-alkoxy-4-methyl-2,3-dihydro-conformation, 3, 630 4H-Pyran, 2-amino-IR spectra, 3, 593 synthesis, 3, 758 4H-Pyran, 4-benzyIidene-synthesis, 3, 762 4H-Pyran, 2,3-dihydro-halogenation, 3, 723 hydroboration, 3, 723 oxepines from, 3, 725 oxidation, 3, 724 reactions, with acids, 3, 723 with carbenes, 3, 725 4H-Pyran, 5,6-dihydro-synthesis, 2, 91 4H-Pyran, 2,6-diphenyl-hydrogenation, 3, 777 4 H-Pyran, 6-ethyl-3-vinyl-2,3-dihydro-reactions, with acids, 3, 723 4H-Pyran, 2-methoxy-synthesis, 3, 762 4H-Pyran, 2,4,4,6-tetramethyI-IR spectra, 3, 593 4H-Pyran, 2,4,6-triphenyl-IR spectra, 3, 593... 

Beckmann rearrangement, 3, 710 Pyran-4-carbaldehyde, 2,2-dimethyl-tetrahydro-Reformatsky reaction, 3, 732 4 H-Pyran-4-carbaldehydes synthesis, 3, 760-761 Pyran-2-carbonitrile, 5,6-dihydro-reactions, 3, 732... 

The chemometric principle was used to derive a guideline for obtaining a simple yes or no answer about the sterility of food particulates heated at aseptic processing temperatures. A quadratic temperature pulse model was used to estimate bacterial destruction from the fractional yield of thermally produced chemical marker compounds (2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one, M-1, and 4-hydroxy-5-methyl-3(2H)-furanone, M-2) and the rate constants and the activation energies of the chemical and bacterial systems. The model yielded a conservative estimate of lethality at the center of meat-balls heated under different time-temperature conditions. A scheme for determining the minimum marker yield for a designated F -value is provided. 

Kim, M.-O. Baltes, W. On the role of 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one in the Maillard reaction. J. Agric. Food Chem. 1996, 44, 282-289. 

Volatile components formed from the reaction of monosaccharides or disaccharides with P-alanine were investigated in a dry condition as a model system of cookie processing. Maltol is a common compound formed in the Maillard reaction, but it was very difficult to detect it in previous experiments using actual cookie materials. In this work, we investigated the principal compounds and maltol formation from the reaction of monosaccharides or disaccharides with P-alanine at 150 °C for 10 min. Neither the reaction of monosaccharides nor the disaccharides with P-alanine resulted in the formation of maltol. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) was detected as a principal product from the reaction of monosaccharides with P-alanine. 5-Hydroxymethyl-2-furfural was also confirmed as being a major product in both reactions. 

A soln. of 2,6-di- ert-butyl-4-(2,4-dinitrobenzylidene)-4H-pyran in methylene chloride irradiated 1 hr. with a 75 w. flood lamp in a Pyrex flask 2, 6 -di-tert-butyl-l-hydroxy-6-nitro-3-oxospiro-[indoline-2,4 -(4 H)-pyran]. Y 98%. F. e. s. J. A. Van Allan et al., J. Org. Chem. 38, 2834 (1973). 

Identification. Purification and identification of M-1 and M-2 as 2,3-dihydro-3,5-dihydroxy-6-mefliyl-4(H)-pyran-4-one and 4-hydroxy-5-methyl-3(2H)-furanone, respectively, by mass spectrometry have been pubUshed (7,77). Analysis of different types of foods heated similarly at sterilizing temperatures revealed that M-1 is formed in meats and vegetables and M-2 is formed in meats only. Another compound, S-hydroxymediylfiirfural, appears to be a useful marker in heating fruits and fruit juices (M-3X7). 

Bodi 2,3-dihydro-3,5-dihydroxy-6-methyi-4(H)-pyran-4-one (referred to as M-1 for convenience) and 4-hydroxy-5-mediyl-3(2H)-fiiranone (referred to as M-2) have been known for almost 30 years. They were observed in heated foods and synthesized in simple model systems. We were interested in identifying the natural precursors of M-1 and M-2 in real foods. 

In this context, it is interesting that the first examples of mesomorphic CT complexes of discoid or sheet-like donor compounds and a strong electron acceptor [7,7,8,8-tetracyano-1,4-quinodimethane (TCNQ)] constitute an exception from the usually observed behavior. These complexes of bi-4-H pyran or bi-4-H thiopyran derivatives carrying four alkyl- or alkyloxy-phenyl substituents with TCNQ (see Fig. 2), have been prepared as organic conductors [40]. The neat alkylphenyl derivatives in the bi-4-H pyran series and alkyl- or alkyloxy-phenyl-substituted bi-4-H thiopyran donors are mesomorphic [40], but the structures of their mesophases are still not clear. 

Figure 7 Relative amounts of selected compounds from 5.5 g of freshly popped popcorn extracted by SFE DI and SFE SPME methods. B, Sulfurol (4-methyl-5-thiazolethanol), a compound with meaty aroma, was most abundantly observed by the SFE DI method. SFE DI, supercritical fluid extraction direct injection SFE SPME, SFE solid-phase microextraction DDMP, 2,3-dihydro 3,5-dimethyl-4(H)-pyran-4-one.

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