Dimethyl acetal hydrolysis

An alternate method of producing the 21-hydroxy-20-ketone consists in lithium aluminum hydride reduction of the dimethyl acetal, hydrolysis to the 20-hydroxy-21-aldehyde and rearrangement, preferably via the bisulfite addition product... 

Step 2 Dimethyl acetal hydrolysis ester hydrolysis followed by decarboxylation intramolecular acid-catalyzed aldol condensation followed by dehydration. 

In a synthesis of Epothilones A and B, Danishefsky and co-workers used a triphenylsilyl ether to protect a hindered secondary alcohol in a long sequence that included DDQ deprotection of a benzyl ether, dithiane hydrolysis, dimethyl acetal hydrolysis with p-toluenesulfonic acid in dioxane-H20 (5 1) at 50 °CT... 

The rates of both formation and hydrolysis of dimethyl acetals of -substituted benzaldehydes are substituent-dependent. Do you expect to increase or decrease with increasing electron-attracting capacity of the pam substituent Do you expect the Ahydroi to increase or decrease with the electron-attracting power of the substituent How do you expect K, the equilibrium constant for acetal formation, to vary with the nature of the substituent ... 

Formic acid, THF, H2O, 20°, 100% yield. This acetal was chosen to prevent conjugation of a double bond during hydrolysis, which occurred when the corresponding dimethyl acetal was hydrolyzed. ... 

The carbonyl group can be deprotected by acid-catalyzed hydrolysis by the general mechanism for acetal hydrolysis (see Part A, Section 7.1). A number of Lewis acids have also been used to remove acetal protective groups. Hydrolysis is promoted by LiBF4 in acetonitrile.249 Bismuth triflate promotes hydrolysis of dimethoxy, diethoxy, and dioxolane acetals.250 The dimethyl and diethyl acetals are cleaved by 0.1-1.0 mol % of catalyst in aqueous THF at room temperature, whereas dioxolanes require reflux. Bismuth nitrate also catalyzes acetal hydrolysis.251... 

The anodic oxidation of 7-MeO-CHT in MeOH results in the formation of benzalde-hyde dimethyl acetal through a ring contracting rearrangement, whereas 3-MeO-CHT and 1-MeO-CHT are prepared by thermal rearrangement of 7-MeO-CHT and afford 7,7-diMeO-CHT in 83% and 85% yields, respectively, upon the anodic oxidation. The hydrolysis of 7,7-diMeO-CHT in 5% aqueous H2SO4 gives tropone in 85% yield (equation 17). 

In the first method, a dialkylzinc reagent bearing an acetal moiety at the d-posi-tion is used (Scheme 7.25(b)). The catalytic 1,4-addition is followed by acetal hydrolysis and aldol cyclization of the 4-substituted cycloalkanone, affording 6,6- (92), 6,7-, (93) and 6,8- (94) annulated ring systems with high enantioselectivities (>96% ees) [80]. In addition, dimethyl-substituted decalone 95, with a structure frequently found in natural products, is readily obtained in enantiomerically pure form. 

Cyclodextrins slow the rate of hydrolysis of benzaldehyde dimethyl acetal, PhCH(OMe)2, in aqueous acid as the substrate binds in the cyclodextrin s cavity, producing a less reactive complex. Added alternative guests compete for the binding site, displacing the acetal and boosting hydrolysis. 

The product (15-2) from aldol condensation of meto-nitrobenzaldehyde with the dimethyl acetal from ethyl 4-formylacetoacetate (15-1) provides the starting material for a dihydropyridine in which one of the methyl groups is replaced by a nitrile. Reaction of (15-2) with the eneamine from isopropyl acetoacetate gives the corresponding dihydropyridine hydrolysis of the acetal function with aqueous acid affords the aldehyde (15-3). That function is then converted to its oxime (15-4) by reaction with hydroxylamine. Treatment of that intermediate with hot acetic acid leads the oxime to dehydrate to a nitrile. There is this obtained nilvadipine (15-5) [16]. 

Pentenal was employed30 for an effective synthesis of the 2,3-di-deoxy-DL-pentose (50a). The aldehyde was converted into the dimethyl acetal 48 this was ci.s-hydroxylated with potassium permanganate to give diol 49. Mild, acid hydrolysis of 49 afforded the methyl... 

Dimethyl acetals.2 Nafion-H is recommended as catalyst for the synthesis of dimethyl acetals and ethylene thioacetals. It is also useful for hydrolysis of dimethyl acetals. 

Aliphatic acetals Remain unchanged dimethyl acetal43 Hydrolysis dimethyl acetal44... 

Percival and Thomson44 obtained a mixture of disaocharide esters from which, on hydrolysis and derivatization, they isolated 2,3,4,6-tetramethyl-D-galactose anilide and a mixture of methylated acids. From these acids they obtained 3,6-anhydro-2,5-dimethyl-L-galactonic acid, the structure of which was determined by almost the same means as those employed by Jones and Peat.23 On methanolysis of hexamethylagarobiose, Araki28 isolated 3,6-anhydro-2,5-dimethyl-L-galactose dimethyl acetal (XIII),... 

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