Lactones, from ketones

Dicyclopropyl ketones from lactones via y,y -dichloroketones—Self-condensation of lactones <—... 

The methylenation of esters or lactones with 30, followed by further transformation, constitutes a useful synthetic protocol (Scheme 4.27). A carbonyl methyl-enation-Claisen rearrangement strategy using 30 is employed for the construction of medium- and large-ring ketones from lactones [78]. A phenol derivative has also been synthesized by treatment of a protected quinol ester with 30, which involves thermal rearrangement of the intermediate vinyl ether [79]. 

Ketone (16) can be made by the cyclisatlon route" as the y-chloroketone (17) comes from lactone (18)... 

Scheme 6.177 a-Methylenation of ketones [335], lactam formation from lactones [336], urea formation [337], and Knoevenagel condensation [338, 478]. 

Other mechanisms of ketone oxidation are also known and will be discussed in Chapter 8. Peracid, which is formed from aldehyde, oxidizes ketones with lactone formation (Bayer-Villiger reaction). 

However, reactions of PAHs in ambient air to form more polar species (e.g., nitro-PAHs, ketones, quinones, lactones, and dicarboxylic acids) greatly enhance their solubilities in aqueous systems. This has major implications when one considers the distribution of PAHs, and their atmospherically formed PAC derivatives, through the air, water, and soil environments. These increases in solubility upon reaction are important not only from an environmental chemistry perspective but also in terms of possible impacts on public health and ecosystems, e.g., in both the exposure and the health effect... 

Flavor volatQes from beef and pork fat can be concentrated up to 30-fold by extracting with small quantities of SC-CO2 at low pressure. SC-CO2 concentrated volatile fractions from heated beef tallow have greater numbers of terpenoids, more high molecular weight ketones, more lactones, more esters, more phenols and more branched cyclic and unsaturated aldel des than similar extracts from heated pork fat, but the latter has more 2,4-dienals and higher concentrations of aldel des. 

Heat-generated flavors, due to the formation of lactones and methyl ketones from hydroxy and keto add precursors, which occur in trace quantities in milk lai. These flavors arc considered to be desirable in fried and baked goods and are partly responsible for the unique condiment properties of butler in food preparation. However, they are undesirable in dried whole milk and evaporated milk where the objective is to make a bland product as much like fresh milk as possible. 

Cyclohexanone oxygenase from Acinetobacteria converts a variety of alicyclic ketones into lactones in a regio- and enantioselective manner (Table 12). The reaction can be carried out by a whole-cell process (181) or with the isolated enzyme (178). For example, 2-norbomanone [497-38-1] (112) is converted to the corresponding lactone in 81% yield (178). The enzyme, however, is not selective both enantiomers react equally well. The oxidation rate of camphor [76-22-2] (113), is about one-third that of (112) nevertheless, given sufficient amount of time, the product yield reaches 89%. Substituted cylohexanones (114) and cyclopentanones (115) are converted into the corresponding lactones in moderate to good yield and selectivity (179—181). 

Tin-containing silicalite-2, Sn-Sil-2, has been synthesized [107]. From an 119Sn NMR study, however, it has been suggested that Sn4+ ions are mostly in octahedral coordination. Sn-beta catalyzes the Baeyer-Villiger oxidation of cyclic ketones to lactones without using peracids but using H202 [108]. 

The aldehydes are generated at temperatures as low as 60 C. O-f particular note is the oxidation o-f phospholipids and polyunsaturated -fatty acids. It is the oxidative products o-f arachidonic acid -from the phospholipid -fraction in chicken, yielding cis—4-decenal, trans-2-cis—5—undecadienal, and trans-2-cis—4— trans-7—tridecatrienal that are responsible -for the species identity o-f chicken. At temperatures o-f 200 to 300 C the thermal oxidative reactions allow the -formation o-f ketones and lactones as well as aldehydes. 

Just occasionally it is possible to carry out cross-condensations between two different enolizable molecules under equilibrating conditions, A notable example is the base-catalysed reaction between methyl ketones and lactones. With sodium hydride—a strong base that can convert either starting material entirely into its enolate anion—good yields of products from the attack of the enolate of the ketone on the electrophilic lactone can be obtained. 

For Baeyer-Villiger oxidations of ketones into lactones, recombinant whole-cell catalysts were constructed using the CHMO from A. calcoaceticus and cells of S. cerevisiae [127-129] or E. coli [130-132] as host system. These designer cells were used for example for the biotransformation of bicyclo[3.2.0]-hept-2-ene-6-one [133-136], In order to avoid the substrate and product inhibition, an adsorber... 

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