Hydroxy-2-methyl-3 -furanone, 4-

The stereoselective introduction of two methyl groups into / -(- -)-5-hydroxy-methyl-2(5// )-furanone 143 was effected by tritylation followed by the conjugated addition (87JOC1170) of McaCuLi (TMSCl/EtaO, -78°C) and, finally, treatment with LiN(TMS)2/MeI (Scheme 43) (97TL1439). 

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-... 

A rapid and efficient one-pot synthesis of substituted 2(5H)-furanones has been reported starting from 3-hydroxy-3-methyl-2-butanone 88 and ethyl... 

Two molecules of carbon monoxide were successively incorporated into an epoxide in the presence of a cobalt catalyst and a phase transfer agent [29]. When styrene oxide was treated with carbon monoxide (0.1 MPa), excess methyl iodide, NaOH (0.50 M), and catalytic amounts of Co2(CO)8 and hexadecyltrimethylammonium bromide in benzene, 3-hydroxy-4-phenyl-2(5H)-furanone was produced in 65% yield (Scheme 7). A possible reaction mechanism was proposed as shown in Scheme 8 Addition of an in situ... 

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. 

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... 

Ethyl-4-hydroxy-5-methyl-3(2//)-furanone [27538-10-9] and 5-Ethyl-4-hydroxy-2-methyl-3(2//)-furanone [27538-09-6]... 

Trade Names. Sugar lactone (Treatt), Fenugreek lactone (Vioryl). 5-Ethyl-3-hydroxy-4-methyl-2(5)-furanone [698-10-2], abhexone... 

Some representatives of y-lactones are y-valerolactone 150, y-decalactone 151 with peach-like flavour, (Z)-6-dodecen-4-olide 152, 3-methyl-4-octanolide (whiskey lactone) 153 and 3-hydroxy-4,5-dimethyl-2(51T)-furanone (sotolone) 154 (Structure 4.46), found in fenugreek, coffee and sake [1-4, 21-23, 62]. 

Twenty-nine odour-active compounds were detected by using aroma extract dilution analysis (AEDA) [60]. The results of AEDA together with GC-MS analysis showed ethyl 2-methylbutanoate (described as fruity flavour), followed by methyl 2-methylbutanoate and 3-methylbutanoate (fruity, apple-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (sweet, pineapple-like, caramel-like), d-decalactone (sweet, coconut-like), l-( ,Z)-3,5-undecatriene (fresh, pineapple-like), and a unknown compound (fruity, pineapple-like) as the most odour-active compounds. 

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]. 

The influence of the sensitivity of the assessors on AEDA has been studied [11], with the result that the differences in the FD factors determined by a group of six panellists amount to not more than two dilution steps (e.g. 64 and 256), implying that the key odorants in a given extract will undoubtedly be detected. However, to avoid falsification of the result by anosmia, AEDA of a sample should be independently performed by at least two assessors. As detailed in [6], odour threshold values of odorants can be determined by AEDA using a sensory internal standard, e.g. ( )-2-decenal. However, as shown in Table 16.6 these odour threshold values may vary by several orders of magnitude [8] owing to different properties of the stationary phases. Consequently, such effects will also influence the results of dilution experiments. Indeed, different FD factors were determined for 2-methyl-3-furanthiol on the stationary phases SE-54 and FFAP 2 and 2 , respectively. In contrast, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone showed higher FD factors on FFAP than on SE-54 2 and 2, respectively. Consequently, FD factors should be determined on suitable GC capillaries [8]. However, the best method to overcome the limitations of GC-O and the dilution experiment is a sensory study of aroma models (Sect. 16.6.3). 

The production of a closely related furanone starts with natural 5-oxo-glu-conic acid production from glucose with Gluconobacter suboxydans the acid is recovered by precipitation as the calcium salt for flavour applications, it is converted by heating to 4-hydroxy-5-methyl-2H-furan-3-one, a typical savoury reaction flavour with a meat-like taste [70] (Scheme 23.19). 

The major chloroform extractible product from the decomposition of 1-deoxy-l-dibenzylamino-D-fructuronic acid in pH 6.0 buffer is 4-hydroxy-5-methyl-3(2/7)-furanone [78], Treatment of the same Amadori compound in 2N sulfuric acid gives 2-furaldehyde [79],... 

Three analogous processes involved the reaction of the C15 phosphonium salt with the 5-hydroxy-4-methyl-2(5F/)-furanone, in the presence of a base, as described below. 

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