3- Hydroxy-2-furanones. formation

The spiro-dihydrofuran (61) is converted into the cyclobutane derivative (62) under the influence of trifluoroacetic acid. The lithium dienolate (64), derived from the furanone (63), yields solely y-alkylated products on treatment with alkyl halides. Thermolysis of the t-butylperoxybutenolide (65) produces about equal amounts of the hydroxy-furanone (67) and the indenone (68), presumably via the oxide radical (66). Attack of iodide ion on the salt (69) results in the formation of methyl iodide, butanolide, and (surprisingly) methyl 4-iodobutanoate. A description of a study of the photochemical rearrangement of the tetrahydrofurans (70) to the bicyclic oxetans (71) has been presented. ... 

Naim, M., S. Wainish, U. Zehavi, H. Peleg, R.L. Rouseff, S. Nagy, Inhibition by thiol compounds of off-flavor formation in stored orange juice. I. Effect of L-cysteine and N-acetyl-L-cysteine on 2,5-dimethyl-4-hydroxy-3(2H)-furanone formation, J. Agric. Food Chem., 41(9), p. 1355, 1993. 

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

Scheme 22.—Mechanism for the Formation of 4-Hydroxy-5-methyl-3(2/f)-furanone.

An effort has also been made to determine the structure of products providing coloration in the Maillard reaction prior to melanoidin formation. The reaction between D-xylose and isopropylamine in dilute acetic acid produced 2-(2-furfurylidene)-4-hydroxy-5-methyl-3(2/f)-furanone (116). This highly chromophoric product can be produced by the combination of 2-furaldehyde and 4-hydroxy-5-methyl-3(2//)-furanone (111) in an aqueous solution containing isopropylammonium acetate. The reaction between o-xylose and glycine at pH 6, under reflux conditions, also pro-duces " 116. Other chromophoric analogs may be present, including 117,... 

From the reaction of D-ribose-J-14C with secondary amine salts in aqueous acid, Peer and van den Ouweland215 isolated 4-hydroxy-5-methyl-3(2H)-furanone (120) (11.4%), and found it to be labeled entirely at the methyl carbon atom. Thus, in the presence of amines, the formation of 120 must proceed through the 1-deoxydiulose by the mechanism described in Section II (see p. 168). In contrast, the reaction of D-ribose-J-14C 5-phosphate218 gave 120 having no radioactivity in the methyl carbon atom, from which it was concluded that the methyl carbon atom originates from C-5 of the D-ribose. The... 

The routes involved in the formation of the various furan sulphides and disulphides involve the interaction of hydrogen sulphide with dicarbonyls, furanones and furfurals. Possible pathways are shown in Scheme 12.8. Furanthiols have been found in heated model systems containing hydrogen sulphide or cysteine with pentoses [56-58]. 2-Methyl-3-furanthiol has also been found as a major product in the reaction of 4-hydroxy-5-methyl-3(2H)-furanone with hydrogen sulphide or cysteine [21, 59]. This furanone is formed in the Maillard reaction of pentoses alternatively it has been suggested that it may be produced by the dephosphorylation and dehydration of ribose phosphate, and that this may be a route to its formation in cooked meat [21, 60]. 

Scheme 13.14 Formation of 4-hydroxy-2,5-dimethyl-(2H)-furanone from rhamnose...

The reaction of a-bromoacetals with trimethylsilylenolates catalyzed by titanium tetrachloride provides /3-alkoxy-y-bromoketones, which are useful furan precursors (Scheme 33) (75CL527). A new synthesis of acylfurans is exemplified by the formation of the 3-acetyl derivative (146) by heating the brdmoalkene (145) (78JOC4596). 2,2-Dimethyl-3(2//)-furanone (148) has been synthesized from 3-hydroxy-3-methylbutan-2-one treatment with sodium hydride and ethyl formate gave the hydroxymethylene derivative (147), which was cyclized and dehydrated to the furanone (148) with hydrochloric acid (Scheme 34) (71TL4891). O... 

Blank, I., Lin, J., Fumeaux, R., Welti, D.H., and Fay, L.B. 1996. Formation of 3-hydroxy-4,5-di-methyl-2(5H)-furanone (sotolone) from 4-hy-droxy-L-isoleucine and 3-amino-4,5-dimethyl-3,4-dihydro-2(5)-furanone. J. Agric. Food Chem. 44 1851-1856. 

Figure II. Formation of 4-hydroxy-2,5-dimethyI-3(2H)-furanone (HDF) from fructose-1,6-biphosphate via acetylformoine as the intermediate.

Various 7-azi do-h-hydroxy diazo keto esters, e.g. (125), have been found to undergo smooth Rh(II)-catalysed cyclization to afford 2-carboethoxy substituted 3(2//)-furanones as a single diastereoisomer. The authors165 proposed that the formation of e.g. (128) involves insertion of the rhodium carbenoid into the adjacent O—H bond to... 

FIGURE 7.11 Formation of Sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) in wines by aldol condensation of acetaldehyde and 2-oxobutanoic acid followed by lactoni-zation (Kobayashi, 1989). 

A maltol-ammonia browning reaction produced thirteen pyrazines, two pyrroles, two oxazoles, and one pyridine (12). The major products of this system were 2-ethyl-3-hydroxy-6-methylpyridine and 2-ethyl-3,6-dimethylpyrazine. It is difficult to construct possible formation mechanisms for these compounds from maltol and ammonia. All the carbon atoms must come from maltol. It is possible, then, that maltol degrades into smaller carbon units and that these fragments recombine to form larger carbon units, producing these compounds. Recently, the formation of thiophenones and thiophenes from the reaction of 2,5-dimethyl-4-hydroxy-3(2H)-furanone and cysteine or cystine was reported (13. 14). All these reaction mixtures were reported to possess a cooked meat-like flavor. 

Scheme 3.1 Formation of 4-hydroxy-5-methyl-3(2FT)-furanone from a pentose via an Amadori compound and 2,3-enolisation...

The yields of the coloured 2-furfurylidene-4-hydroxy-5-methyl-3(2//)-furanone and 2-furfurylidene-5-methyl-3(2//)-pyrrolinone from xylose and alanine at pH 5 were strongly affected, depending on whether the reaction was carried out at atmospheric pressure or at 400 MPa.109 Formation of both colorants increased progressively... 

Dimethoxy Phenol 3,4-Dimethyl 1,2-Cyclopen tandione 5-Ethyl 3-Hydroxy 4-Methyl 2(5H)-Furanone 3-Ethyl Pyridine Furfuryl Mercaptan Geranyl Isovalerate 2,3 -Heptandione (Z)-3-Hexenyl Butyrate (Z)-3-Hexenyl Formate Hexyl Butyrate Hexyl Hexanoate Isoamyl Isobutyrate Isobutyl Formate Isobutyl Hexanoate Linalool Oxide... 

Furan derivatives have been used to inhibit the formation of melanin when combined with other agents <2000JPP2000302642>. For the group consisting of 5-methyl-2(3//)-furanone 86, 2,5-dimethyM-hydroxy-3(2//)-thiophenone, 2-buten -olide, and 2-hydroxymethylfuran 21, the in vitro formation of tyrosinase was inhibited by... 

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