Methyl-477-pyrans

A synthetic procedure to insert the perfluoroalkyl group into the dihydropyrone cycle via ethoxybutenone has been elaborated (98T2819). 6-Ethoxy-2-trifiuoro-methyl-4//-pyran-4-one (309) was synthesized by the condensation of ethyl... 

The exclusive and quantitative formation of oxepins upon Pd-catalyzed decomposition of 4-diazomethyl-4-methyl-4 //-pyrans (Entry 11) contrasts with the results of the CuCl-promoted reaction which affords a 2 1 mixture of oxepin (by 1,2-C migration) and 4-methylene-4//-pyran (by 1,2-H migration) under otherwise identical conditions 381J. When the methyl group at C-4 of the diazo precursor is replaced by H, the metal-catalyzed route to thiepins is no longer viable Pd- or Cu(I)-catalyzed decomposition of 4-diazomethyl-4//-thiopyrans invariably leads to 4-methylene-4H-thiopyrans 378 (Entry 10). Only the proton-catalyzed decomposition of these diazo compounds affords the desired thiepin, albeit in low yield 378). 

Scheme 5.—Formation of 3-Hydroxy-6-methyl-4//-pyran-4-one from Dihydroxyace-tone.

Thermolysis of D-fructose in acid solution provides 11 and 2-(2-hydrox-yacetyl)furan (44) as major products. Earlier work had established the presence of 44 in the product mixtures obtained after acid-catalyzed dehydrations of D-glucose and sucrose. Eleven other products were identified in the D-fructose reaction-mixture, including formic acid, acetic acid, 2-furaldehyde, levulinic acid, 2-acetyl-3-hydroxyfuran (isomaltol), and 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2//)-furanone (59). Acetic acid and formic acid can be formed by an acid-catalyzed decomposition of 2-acetyl-3-hydroxyfuran, whereas levulinic acid is a degradation prod-uct of 11. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one has also been isolated after acid treatment of D-fructose.The pyranone is a dehydration product of the pyranose form of l-deoxy-D-eo f o-2,3-hexodiulose. In aqueous acid seems to be the major reaction product of the pyranone. 

Hydroxy-2-methyl-4//-pyran-4-one (maltol) and 2-acetyl-3-hydroxy-furan (isomaltol) are also products of the Maillard reaction. Both have a considerable history, due to their early detection in beer and breads. A mechanism based upon the pyranose form of a methyl-a-dicarbonyl inter-... 

The best approach to unsubstituted 4//-pyran (5) is from glutaric dialdehyde and hydrogen chloride, which gives up to a 40% yield of 5. Intermediate 23 is not isolated.9,19,57 This procedure was successfully extended to the preparation of 4-methyl-4//-pyran.7... 

The hydrogenation of 2-diethylamino-6-methoxy-3-methyl-4//-pyran (96a) on Pd-charcoal led to hydrogenolytic ring cleavage, yielding 60% of... 

Figure 7.1. Structures of volatile compounds characterized from toasty caramel aroma released in wine from toasted woods during aging. (1) 3,5-dihydroxy-2-methyl-4//-pyran-4-one (2) 3-hydroxy-2-methyl-477-pyran-4-one (3) 2,3-dihydro-3,5-dihydroxy-6-methyl-4//-pyian-4-onc (DDMP) (4) 4-hydroxy-2,5-dimethylfuran-3 ( 2H)-one (furaneol) (5) 2,3-dihydro-5-hydroxy-6-methyl-47T-pyran-4-one (dihydro-maltol) (6) 2-hydroxy-3-methyl-2-cyclopenten-l-one (or cycloteme) (Cutzach et al., 1997).

Dialdehydes 3 were cyclodehydrated to methyl-4//-pyrans 4 (R = Me, R = H R = H, R = Me), and the same method was successfully used for the preparation of 2,5-dideuterated 2 from 1,4,4-trideuterio-glutaric dialdehyde (860MS459). 

Amino-3,5-dicyano-4-isopropyl-6-methyl-4//-pyran 1598,1648,16 87JST19... 

Kim M.O. and Baltes W. (1996) On the role of 2,3-dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one in the Maillard reaction. J. Agric. Food Chem. 44, 282-9. 

Mills F.D., Weisleder D. and Hodge J.E. (1970) 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one, a novel nonenzymatic browning product. Tetrahedron Lett. 15, 1243-6. 

Ehnenhorst, H. and G. Nicolaus Dihydro-y-pyrone im Tabakrauch. Nachweis von 2,3-Dihydro-5-hydroxy-6 -methyl-4//-pyran-4-one in Rauch von Cigaretten aus Burley-, Vhginia-, und Orienttabaken [Dihydro-y-pyrones... 

To a solution of 1.0 mmol aldehyde and 0.1 mmol diol in 0.5 mL toluene at -40°C (temperature of the cooling bath) was added 0.5 mmol ( )-l-dimethylamino-3-tert-butyldimethylsiloxy-1,3-butadiene dropwise (5-10 s). The reaction was maintained at the temperature for 1 day. The reaction was then brought to -78°C (dry ice/acetone) before dilution with 1.0 mL CH2CI2 and subsequent addition of 1.0 mmol acetyl chloride. This was allowed to stir for 30 min at -78°C before the crude mixture was transferred directly on top of a silica gel column and eluted with hexanes/EtOAc to afford 75% 2,3-dihydro-2-methyl-4//-pyran-4-one as a pale yellow oil, with 97% e.e. 

Dimethyl-1,3-pen tadienyl)-2-methoxy-3-methyl-4//-pyran-4-one, D-20233 6-( 1,3-Dimethyl-1,3-pentadienyl)-4-methoxy-3-methyl-2//-pyran-2-one, D-20234... 

To estimate the content of dihydro-2,5-dihydroxy-6-methyl-4//-pyran-4-one (DDMP) saponin and saponin B in selected pea cultivars, an HPTLC method was developed [35]. Silica gel 60 F254 plates were prewashed with methanol and activated at 100°C prior to development in automated multiple development chamber AMD2 using chloroform-methanol-water (55 37 8, v/v). Densitometry, after postchromato-graphic derivatization with anisaldehyde-sulfuric acid, revealed the prevalence of saponin B over DDMP saponin in all pea cultivars. The identities of the two com-ponnds were determined by coupling HPTLC directly to ESI-MS and additionally by offline MALDI-TOF/TOF-MS by application of a purified extract/matrix mixture onto a standard steel MALDI plate. HPTLC plates intended for MS analysis were developed with a modified developing solvent chloroform-methanol-water (6.5 3.5 0.9, v/v). The analytes were eluted from the plates with 0.1% formic acid-acetonitrile (40 60, v/v) by means of TLC-MS interface (CAMAG) and transferred into the ESI-MS system, which operated in positive-ion mode. 

Figure 1. High performance liquid chromatogram of products from cookies backed with fructose at 150°C for 10 min. Chromatographic conditions column DEVELOSIL ODS-5 (4.6 mm i.d. x 250 mm), mobile phase H -MeOH (6 1 v/v), flow rate 0.8 ml/min, UV detection 283 nm, chart speed 5 mm/min. (3) 2,3-dihydro-3,4-dihydroxy-5-acetylfuran, (5) 2,3-dihy-dro-3,5-dihydroxy-6-methyl-4-(//)-pyran-4-one,...

Pyran, 4-methyl-4//-pyran, and 1,4-dimethyldihydropyri-dine are regiospecifically metalated at the position next to the heteroatom by means of n-butyllithium/potassium ferf-butoxide. ... 

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