3- methyl-3- furans Subject

Fig (19) Octalin ketal (163) is converted to kete dithioacetal (164) by the cleavage of ketal function and condensation with carbon disulfide and methyl iodide. Subjection of (164) to the action of dimethylsulfonium niethylide and acid hydrolysis leads to the formation of unsaturated lactone (165).lts furan silyl ether derivative is caused to undergo Diets-Atder reaction with methyl acrylate to obtain salicyctic ester (166) which is converted by standard organic reactions toabietane ether (167). It is converted to aiiylic alcohol (168) by epoxidation and elimination. Alcohol (169) obtained from (168) yields orthoamide which undergoes transformation to amide (170). Its conversion to the previously reported intermediate has been achieved by epoxidation, elimination and hydrolysis. 

In contrast with the above situation, the polymerization of 2-furfurylidene methyl ketone, di-2-fiirfurylidene ketone and their homologues has been the subject of a large volume of (mainly technical) publications because of the useful applications of the final cross-linked products. As pointed out in the introduction, this review does not deal with the technological aspects of furan resins and in this section only the mechanistic aspects of the first phase of these polymerizations will be discussed. 

The study of monosaccharides subjected to conditions of methanolysis is considered for two reasons. First, the decomposition of monosaccharides is indicative of the decomposition of monosaccharides liberated during methanolysis second, the ratio of methyl glycosides of a particular standard monosaccharide is the same for the same monosaccharide released during methanolysis (for a particular set of methanolysis conditions), provided that the concentration of sugars is relatively low. Up to four methyl glycosides (the a and )8 anomers of the pyranoside and furan-oside forms) of a particular monosaccharide may be formed the acyclic dimethyl acetal is an additional possibility. The ratios of methyl glycosides of 10 monosaccharides subjected to methanolysis with M hydrogen chloride for 24 h at 80° has been reported. Similar information is also available in another study."... 

The conformational preferences of 2- and 3-monosubstituted derivatives of furans, thiophenes and pyrroles have been the subject of ab initio MO studies (77JCS(P2)160l, 78JA3981,79JA311). Of the systems considered, experimental information from microwave spectroscopy is available for 2- and 3-methyl... 

Non-aryl substituted isomiinchnones also undergo the same transformation but under less rigorous conditions. Thus, when acyclic diazoimides 19 and 20 were subjected to Rh2(OAc)4-catalyzed decomposition in the presence of DMAD, cycloaddition followed by extrusion of methyl isocyanate occurred to give the substituted furans 94 and 95 [35]. 

Alternatively, furan may also be brominated and then subjected to an exhaustive methanolysis. A zinc chloride-catalysed double enol ether condensation with 1-propenyl methyl ether (Miiller-Cunradi-Pieroh reaction) gives finally the crystaUine (aU )-Cio-dialdehyde in an overall yield of >50 %. 

In the case of methyl ethers of MBH adducts, the reaction proceeds through p-C-H activation to provide the substituted dihydrofurans 396, which have been subjected to in situ treatment with TMSOTf/EtaN, affording substituted furan rings 397 in moderate to good yields (Scheme 3.174). ... 

The investigation of characteristic flavors associated with cooked meats has been the subject of much research over the past four decades but, although compounds with "meaty" aromas had been synthesized, compounds with such characteristics were not found in cooked meats until recently (1). In the search for compounds with characteristic aromas it was found that furans and thiophenes with a thiol group in the 3-position possessed meat-like aromas (2). The corresponding disulfides formed by oxidation of furan and thiophene thiols were also found to have meat-like characteristics, and exceptionally low odor threshold values (3). A number of such compounds are formed in heated model systems containing hydrogen sulfide or cysteine and pentoses or other sources of carbonyl compounds (4,5), The thermal degradation of thiamine also produces 2-methyl-3-fiiranthiol and a number of sulfides and disulfides (6J). 

GC-MS has been apphed to studying the nature of the oxidation products of CLA (86-89). The subject has been reviewed by Yurawecz and colleagues (86,89). Furan fatty acids were major products that could be oxidized further to give, for example, oxofuran fatty acids. Similar to the analysis of CLA, long polar capillary GC columns were employed. Other than methyl esters, no special derivatives have been used. 

Furan and its derivatives have been subjects of interest for several years, given their roles in several combustion processes, and this interest has expanded significantly in the past decade as attention to biomass-derived fuels has increased. This section wiU summarize mechanistic studies of the pyrolytic and oxidative chemistry of furan and its substituted derivatives (Figure 10). Studies of the combustion pathways of furan and its methyl-substituted derivatives are particularly intertwined together, these studies provide a comprehensive case of foUowing initial mechanistic studies through the development of a fuU chemical kinetic mechanism. 

The reaction of OH with 5-methyl-3H-furan-2-one has been the subject of a relative rate study by Bierbach et al. (1994). Details are given in table VII-D-3. The result of... 

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