Diethylacetal, hydrolysis

Hydrolysis of the diethylacetal function employing p-toluenesulphonic acid in acetone, pyridinium p-toluene-sulphonate in EtOH, and a suspension of Si02 in hexane. In all cases the corresponding aldehyde is obtained in high yield as a Z E isomeric mixture. Transmetallation of acetal with Me2Cu(CN)Li2 followed by treatment with c-hexenones giving the 1,4-addition product. Alternatively, transmetallation with n-BuLi and reaction with benzaldehyde giving the expected alcohol. 

Methimazole Methimazole, l-methyl-2-imidazolthiol (25.2.5), is synthesized by reacting aminoacetic aldehyde diethylacetal with methylisothiocyanate and snbseqnent hydrolysis of the acetal group of the resulting disubstituted urea derivative 25.2.4 by a solution of sulfuric acid, during which a simultaneous cyclization reaction takes place, forming the imidazole ring of the desired methimazole [15,16]. 

Fig. 21. Hydrolysis of acetals at 20°C on a Dowex 50W X10 resin catalyst [513]. Rate coefficients of the resin-catalysed reaction (feres) versus rate coefficients of the reaction catalysed by dissolved inorganic acid (fehom)- 1 Formaldehyde dimethylacetal 2, formaldehyde diethylacetal 3, formaldehyde di-2-propylacetal 4, acetaldehyde ethyleneacetal 5, acetone ethyleneacetal 6, acetaldehyde dimethylacetal 7, acetaldehyde diethylacetal. The slope for acetals 1—3 is 1, for the acetals 3—7 0.5.

The pH-rate profile for unbuffered hydrolysis of glyceraldehyde-3-phosphate (6-3-P) has been attributed to hydrolysis of the monoanion of the phosphate monoester at pH < 4, spontaneous formation of glyceraldehyde from the phosphate dianion at pH 7-8, and, at higher pH, hydroxide-catalysed methylglyoxal formation. Reaction of the dianion is not subject to a solvent isotope effect and is believed to occur by the irreversible ElcB mechanism whereby an enediolate intermediate, formed on rate-determining C(2) deprotonation, subsequently expels phosphate trianion by C—0 bond breaking. The diethylacetal and 2-methyl-G-3-P do not hydrolyse under the same conditions.5... 

Compound 164 was readily synthesized in two steps starting from 2-fluoro-5-nitrobenzaldehyde diethyl acetal 162 by nucleophilic substitution. Acidic hydrolysis of the diethylacetal function of 163 restored the aldehyde group, followed by spontaneous cyclization yielding oxazepine 164 (Scheme 25) <2004TA2555>. 

Functionalized enantiopure 5,6-dihydropyran-2-ones 917 are accessible from a Cu(n)- (BOX) catalyzed reaction of ketene diethylacetal 914 and a-dicarbonyl compounds 915 followed by hydrolysis of intermediate 916 with formic acid (Scheme 249, Table 42) <2000JA11543>. 

This difference in driving force is used in the dimethyl-or diethylacetalizations of carbonyl compounds with orthoformic acid esters since these acetalizations are simply linked with the hydrolysis of an orthoester into a normal ester. 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Catalytic activity of rare earth elements (i.e., lanthanides, symbol Ln) in homogeneous catalysis was mentioned as early as 1922 when CeCls was tested as a true catalyst for the preparation of diethylacetal from ethanol and acetaldehyde [1]. Solutions of inorganic Ln salts were subsequently reported to catalyze the hydrolysis of carbon and phosphorous acid esters [2], the decarboxylation of acids [3], and the formation of 4-substituted 2,6-dimethylpyrimidines from acetonitrile and secondary amines [4]. In the meantime, the efficiency of rare earth metals in heterogeneous catalysis, e. g., as promoters in lanthanide (element mixtures)-... 

An elegant synthesis of pelletierine acetal has been reported (497) although it has not yet been possible to synthesize the alkaloid itself. /3-(2-pyridyl) - propionaldehyde diethylacetal, obtained in 28-29% yield from lithium picolyl and bromoacetal, is hydrogenated in glacial acetic acid over a platinum catalyst to 3-(2-piperidyl)-propionaldehyde diethylacetal. It is of interest to note that if the hydrogenation be carried out in dilute solution, the product is 6-coniceine (498). However, hydrolysis of the acetal succeeds only if the secondary nitrogen is first blocked (497, 518). 

The synthesis of 4-carboxyl-1,2,3-triazoles and derivatives has been an active field of study, and the variety of methods developed is impressive. One of the earliest reactions is the oxidation, usually with silver oxide, of the formyl group (Eq. 21). Sheehan and Robinson have reported the first example of phenyl azide addition in which both isomeric products were isolated (Eq. 22), and they demonstrated the structures of 4.2-1 and 4.2-2 by oxidation. Similar results were obtained using the diethylacetal of propy-nal followed by hydrolysis. 

The nthesis of 2,3-dideoxy-3-C-methylene-D- /ycero-pentofuranose has been achieved by Sharpless epoxidation of 5,5-diethoxy-3-methyl-2-pentenal followed by rearrangement of the product to 2,3-dideoxy-3-C-methylene-D-g/ycero-pentose diethylacetal and, finally, hydrolysis. ... 

An interesting amine migration followed by a Claisen rearrangement occurs on heating the condensation product of 2-methyl-3-propyn-2-ol with dimethylaceta-mide diethylacetal (Scheme 41). Acid hydrolysis of the products leads to a 4-oxohexanoate. 

The hydrolysis of the diethylacetals of acetaldehyde (I), croton aldehyde (II), ben-zaldehyde (III), citral (IV) was realized with stirring at 293 K in the presence of the cation-exchange resin. The tetraethyl diacetals of glutaraldehyde (VI), 1,2-diformyl-f n-dichlorocyclopropane (VII), and fumaraldehyde (VIII) are hydrolyzed in a similar manner. 

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