Acetalization, tandem

Scheme 5.69 Types of hydroformylation-acetalization tandem reactions.

Application of the Hydroformylation-Acetalization Tandem Reaction in Practice... 

Beginning with the only occasionally observed formation of acetals as final products of hydroformylation reactions, the hydroformylation-acetalization tandem reaction is nowadays one of the most important reactions in the framework of hydroformylation. Today, the undesired formation of acetals can be avoided by special setup of the reaction conditions. On the other hand, the tandem reaction is an important protocol for the protection of the carbonyl groups toward several... 

Special hydroformylation protocols allow the one-step production of alcohols (hydroformylation-hydrogenation tandem reaction, see also Section 5.2), which are also of crucial importance as aroma compounds. Acetals, which have similar odors like their aldehydic precursors, maybe produced in the hydroformylation in alcohols as solvent under acidic conditions (hydroformylation-acetalization tandem reaction, see also Section 5.3) [15]. The acetal formed protects the aldehyde toward oxidations, reactions with amines, or aldol condensations. Especially in demanding fragrances, these modifications that may affect the scent impression are not desired. 

The syntheac potenQ of the tandem [4+2 /[3+2 cycloadchtion process is greatly enhanced by the employment of vmyl ether dienophiles For example, the nse of vmyl bntyl ether as a chenophile leads to a tnoyclic nirroso acetal, which gives a tncyclic lactam, as shown m Eq 8113... 

When a-tethered nitro ilkenes bearing three or four methylene chains and ester-activated dipolarophiles react with vinyl ethers, splro mode tandem cycloaddidon takes place to give tricyclic splro nitroso acetals In good yield and high diastereoselecdvity CScheme 8.46. ... 

Shi, F.-Q., Li, X., Xia, Y, Zhang, L. and Yu, Z.-X. (2007) DFT Study of the Mechanisms of In Water Au(I)-Catalyzed Tandem [3,3]-Rearrangement/Nazarov Reaction/[l,2]-Hydrogen Shift of Enynyl Acetates A Proton-Transport Catalysis Strategy in the Water-Catalyzed [l,2]-Hydrogen Shift. Journal of the American Chemical Society, 129, 15503-15512. 

In another example, a multiresidue method using HPLC/ESI-MS was developed to determine six imidazolinone herbicides in five different soil types. Good recoveries (80-120%) and adequate sensitivity at the 2.0 ngg level were obtained for the compounds investigated. In the method, a 50-g soil sample was extracted for 1 h in 0.5N NaOH solution. A portion of the extract was acidified, to precipitate the humic acids, and the supernatant was then loaded on to a preconditioned trifunctional Cig SPE cartridge and eluted with ethyl acetate. Further cleanup was achieved using a tandem strong anion-exchange (SAX)-SCX SPE combination. Analytes were eluted... 

Thermospray ionisation sources are usually outfitted with a quadrupole or magnetic sector mass spectrometer (including hybrids or tandem forms). Thermospray operation allows a reversed-phase solvent system, e.g. a 50 50 (v/v) water-methanol or acetonitrile mix containing 0.1 M ammonium acetate. This ensures compatibility with the universal HPLC procedures available in many industrial research laboratories. 

A mixture of 1,4-dioxane and water is often used as the solvent for the conversion of aldehydes and ketones by H2Se03 to a-dicarbonyl compounds in one step (Eq. 8.117).331 Dehydrogenation of carbonyl compounds with selenium dioxide generates the a, (i-unsaturated carbonyl compounds in aqueous acetic acid.332 Using water as the reaction medium, ketones can be transformed into a-iodo ketones upon treatment with sodium iodide, hydrogen peroxide, and an acid.333 Interestingly, a-iodo ketones can be also obtained from secondary alcohol through a metal-free tandem oxidation-iodination approach. 

Barrero, Oltra and coworkers reported on the use of epoxygeranyl acetate in titanocene-mediated cyclizations and found that the termination of the reaction took place via a /i-hydride elimination after trapping of the radical by the second equivalent of Cp2TiCr [94,95]. This finding together with Takahashi s tandem cyclization [96] (see below) marks the first example of extremely interesting developments in epoxypolyene cyclizations via radicals that are discussed separately in the following section. 

Fox, A. Krahmer, M. Harrelson, D. Monitoring muramic acid in air (after alditol acetate derivatization) using a gas chromatography-ion trap tandem mass spectrometer. J. Microbiol. Meth. 1996, 27,129-138. 

Inter [4+2]/inter [3+2] The tandem intermolecular [4+2]/intermolecular [3+2] cycloadditions create bicyclic nitroso acetals with up to six stereogenic centers, which can be controlled by the choice of the stereochemistry of each component and the Lewis acids. The nitronate derived from 2-nitrostyrene and 1-trimethylsilyloxycyclohexene reacts with methyl acrylate to give the nitroso acetal in good yield and high diastereoselectivity (Eq. 8.107).154... 

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