Dehydration fragmentation

Simple sugar dehydration/fragmentation products furans, pyrones, cyclopentenes, carbonyl compounds, acids... 

Specify the amount of d-fructose that survived questions the relevance of the data. A typical product profile for D-fructose decomposition is shown in Table 1. Here it is sufficient to note that acid-catalyzed degradation of reducing sugars proceeds in a complex reaction network to products of isomerization, dehydration, fragmentation, and condensation. 

Sucrose is unstable at temperatures albO C (320T) and thermolyzes to the brown candy that we appreciate as caramel. Caramel contains a myriad of decomposition products formed by simultaneous cleavage of sucrose to glucose and fructose, dehydrations, fragmentations (such as retroaldol additions), isomerizations through enols (apply the last three reactions to glucose and see what you get), and polymerizations. Two of the odorants that have been identified in the mixture are shown below. 

Alkaline Dehydration, Fragmentation, and Oxidation Reactions of Carbohydrates... 

Solution 2-Methyl-3-pentanol, an open-chain alcohol, has M+ = 102 and might be expected to fragment by o- cleavage and by dehydration. These processes would lead to fragment ions of m/z = 84, 73, and 59. Of the three expected fragments, dehydration is not observed (no m/z = 84 peak), but both a clea iges take place (m/z = 73, 59). 

Figure 17.14 Mass spectrum of 1-butanol (M+ = 74). Dehydration gives a peak at mjz - 56, and fragmentation by alpha cleavage gives a peak at m/z = 31.

The acetate labeling results clearly demonstrated a polyketide origin for the naphthoate fragment. This resulted in the hypothesis that the first enzyme-free intermediate in azinomycin biosynthesis would be naphthoate 102, with condensation to fonn a polyketone chain, reduction, cyclization, and dehydration/aromati-... 

Aldoximes are readily dehydrated with N, N -carbonyldiimidazole (CDI). An intermediate azolide is formed in the process under elimination of one mole of imidazole, which fragments into a nitrile through elimination of CO2 and a second mole of imid-azole.[1],[2]... 

Phomactin A is the most challenging family member architecturally. The fragments that are most challenging are highlighted in Fig. 8.4. In Box-A, the highly sensitive hydrated furan is prone to dehydration under acidic or basic conditions, and any total synthesis almost certainly must save introduction of this fragment until the end game. Box-B relates to the strained and somewhat twisted electron-rich double bond. This trisubstituted olefin is extremely reactive toward electrophilic oxidants. 

Each transformation shown in Scheme 3.104 involves consecutive reactions, for which optimal procedures were found. For example, path b involves four transformations successive reduction of the nitronate fragment to the oximino group and then to the imino group followed by keto imino condensation and dehydration of intermediate pyrroline. 

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