Furans and furanones

Under the conditions corresponding to the roasting of coffee, serine, threonine, and sucrose yield various substituted pyridines (51), furans, and furanones (52). Thirty-three pyridine derivatives were identified by Baltes and co-workers (51), Recently, 3-methylthiomethylpyridine was identified as one of the products of thermal degradation of the glucose-methionine Amadori intermediates (53). 

Alkylpyrazines. Besides the sugar-derived carbonyls, Strecker aldehydes, furans, and furanones were identified from the model systems (WGH-G, DWGH-G, and AWGH-G). 

Baltes W. and Bochmann G. (1987a) II. MS identification of furans and furanones from the reaction of serine and threonine with sucrose under the conditions of coffee roasting. Z. Lebensm. Unters. Forsch. 184, 179-86. 

Table 2 shows the relative quantities of component groups in the volatiles after heating mixtures of glucose or fructose with serine at 120°, 150° and 180° C. It shows optimal formation of furans and pyranones at 120° C, whereas furanones possess a maximum at 150° C. Compounds of the other groups are formed preferentially at 150° C, while the formation of pyrazines proceeds better the higher a reaction temperature was chosen. Also pyrroles need higher temperatures for their formation. So we could demonstrate that only acetylpyrrole and 5-methylpyrrole-2-aldehyde has been formed at 120° C whereas many additional pyrroles appear at 150° C or 180°C respectively (12). 

Furans and 2-furanones (butyrolactones and butenolides) are main sources of heterocycles for pyridazine syntheses. A furan ring attached to a ribofuranosyl ring is readily transformed with hydrazine to give py-ridazine-3-C-nucleoside (83JOC2998 87JOC4521). Similarly, photooxi-... 

The Cj p3-O bond of 2-tert-butoxy-furan and -thiophene is cleaved catalytically by BiCl3 or Bi(OTf)3 to produce 2(5H)-furanone and -thiophenone, respectively [254]. The selective hydrolysis of aryl esters is catalyzed by bismufh(III) mandelate in DMSO [255]. In the presence of 50 mol% Bi(NO3)3-5H2O, 10 mol% Cu(OAc)2, and Montmorillonite KIO ketoximes undergo facile deoximation in acetone-H2O [256]. Under microwave irradiation the BiCls-promoted hydrolytic cleavage of the C=N bond of dimethylhydrazines, tosylhydrazines, semicarbazones, and oximes proceeds in wet THF (Scheme 14.120) [257-259]. 

There are several studies investigating the flavor composition of smoked products that gives the products their characteristic flavors. The main components responsible for the smoke flavor are phenol derivatives. In addition to the flavoring compounds arising from wood pyrolysis, flavoring compounds derived from plants are also present. The soluble fraction mostly contains fatty adds and fatty esters, in addition to acids, alcohols, carbonyls, esters, furans, lactones, furans, and many miscellaneous compounds [108]. The phenolic fraction of traditional kiln-smoked Bacon contains phenols, furfuryl alcohol, and cyclotene while different compounds, such as 2,4,5-trimethyl-3(2//)-furanone, have been isolated from cooked Oscar Mayer bacon [109],... 

The Maillard reaction between reducing sngars and amino acids under specific conditions (pH, water activity, and temperature) is primarily responsible for the production of heterocyclic volatile compounds such as pyrazines, pyridines, pyrroles, furans, and the Strecker aldehydes. Maillard reactions produce many potent aroma compounds identified in some roasted tree nuts, including 3-methylbutanal, 2,3-butanedione, methional, phenylacetaldehyde, 2-ethyl-3,5-dimethylpyrazine, and 2,5-dimethyl-4-hydroxy-3(2//)-furanone, among others. 

The formation of furans, thiophenes, furanones, thiophenones etc. was investigated in a series of [l(or 6)- C]-glucose and [l- C]-arabinose/ cysteine and methionine model experiments. The labeled compounds were analyzed by capillary GC/MS and NMR-spectroscopy. From their structures the degradation pathways via different reactive intermediates (e.g. 3-deoxyaldoketose, 1-deoxydiketose) and fragmentations were evaluated. Besides the transformations to flavor compounds via identical labeled precursors, major differences in the flavor compounds result from specific Strecker reaction sequences. Major unlabeled compounds e.g. 3-mercaptopropionic acid from cysteine and 4-methylthiobutyric acid from methionine demonstrate transamination/reduction, and the formation of pyruvate and 2-mercaptopropionic acid from [l-i C]-glucose/cysteine indicates B-elimination. 

Diol (1) is used to prepare cyclopropenone acetal (2). Its highly nucleophilic double bond forms addition products with alcohols and amines and cycloaddition products with dienes to give norcarenes, ketones to give furanones and oxetanes, aldehydes to give butenolide, furan, and y-keto ester derivatives (eq 2), electrophilic alkenes to give cyclopropanes and functionalized cyclopentenones, and an a-pyrone to give a... 

The reaction of the o-iodophenol 275 with an alkylallene affords the bcnzo-furan derivative 276[184], Similarly, the reactions of the 6-hydroxyallenes 277 and 279 with iodobenzene afford the tetrahydrofurans 278 and 280. Under a CO atmosphere, CO insertion takes place before the insertion of the allenyl bond, and a benzoyl group, rather than a phenyl group, attacks the allene carbon to give 280. Reaction of iodobenzene with 4,5-hexadienoic acid (281) affords the furanone derivative 282[185]. 

Fischer-type carbene complexes in the synthesis of furan, pyrrole, 5//-furanone, and 5//-pyrrolone derivatives 98YGK413. 

PHOTOINDUCED-ADDITION OF METHANOL TO (5S)-(5-0-tert-BUTYLDIMETHYLSILOXYMETHYL)FURAN-2(5H)-ONE (4R,5S)-4-HYDROXYMETHYL-(5-0-tert-BUTYLDIMETHYLSILOXYMETHYL)FURAN-2(5H)-ONE (2(5H)-Furanone, 5-[[[(1,1-dimethylethyl)dimethylsilyl]oxy]methyl]-, (S)-and D-erythro-Pentonic acid, 2,3-dideoxy-5-0-[(1,1-dimethylethyl)dimethylsilyl]-3-(hydroxymethyl)-, y-lactone)... 

Although the preparative chemistry of (vinylketene)cobalt(I) complexes is relatively limited in the literature, the methods used include all the major procedures that have been more widely exploited in the analogous chromium and iron systems. There are many similarities between the intermediates involved in the synthesis of vinylketene complexes of iron, chromium, and cobalt, but as the metal is varied the complexes containing analogous ligands often exhibit significant differences in stability and reactivity (see Sections II and VI). Comparison of such species has often been an important aim of the research in this area. The (vinylketene)cobalt(I) complexes have also been shown to be synthetically useful precursors to a variety of naphthols, 2-furanones, ce-pyrones, phenols,6,22,95 >8, y-unsaturated esters,51 and furans.51,96a... 

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