Hydrolysis of ketals

The aromatization of the oxepin structure can be accompanied by other acid-catalyzed reactions such as the hydrolysis of ketals. Dimethyl 11 -oxo-6-oxabicyclo[5.4.0]undeca-l (7),2,4-triene-2,3-dicarboxylate ethylene ketal reacts in the presence of trifluoroacetic acid to give the tetralone system 3.133... 

By hydrolysis of ketals or thioketals Amberlyst ion-exchange resin, 152 Methylthiomethyl p-tolyl sulfone, 192 From oximes... 

As shown in Scheme 17,180 was available from the common, totally synthetic, intermediate 17. Using reported methodology for the introduction of vinylsilanes,57 17 was reacted smoothly with (methoxy dimethylsilyl) trimethylsilyl methyl-lithium in pentane to afford (EIZ) vinyl silane 220 in 54% yield. The main by-product in this reaction was ketone 17, which could be recycled thus, based on recovered 17, the yield of 220 was 93%. Hydrolysis of ketal 220 occurred without protodesilylation upon exposure to aqueous oxalic acid absorbed onto silica gel to give ketone 221 in 80% yield. Upon low-temperature ozonolysis of 221 in methanol, a remarkably stable dioxetane 223 was produced, as evidenced in the H NMR... 

First-order rate coefficients of hydrolysis of ketals and orthoesters in equimolar mixtures of CD3OD and DjO with 0.006 M acetate buffer, half-neutralized, at 25 °C [187]... 

Weakly acidic ion exchange resins containing carboxylic groups have been much less studied as catalysts. An interesting example is that of polymer 15, a linear poly(N-isopropylacrylamide), which is soluble in cold water but insoluble in water heated above the critical solution temperature, facilitating its recovery and reuse. Such materials have been tested as catalysts for the hydrolysis of ketals [79],... 

Diiodosilane (DIS) reagent for mild hydrolysis of ketals, acetals or reductive iodination of ketones and aldehydes (see 1st edition). 

Figure 7.6 compares the performance of the equations of Hammett and Taft with respect to the hydrolysis of ketals that proceed according to mechanism (7.VII) [7]. 

Many chemical reactions are catalyzed by acids but on a large-scale can generate significant amoimts of acid waste, which requires neutralization and/ or disposal. In principle, CO dissolved in water is mildly acidic, due to formation of carbonic acid and should be capable of catalyzing a range of reactions. Simple pressure release at the end of the reaction brings the pH back to levels, which require minimal neutralization. Hydrolysis of ketal to cyclohexanone and ethylene glycol and epoxides to diols are a few examples where CO in presence of water have been used as a catalyst [322]. 

Oxidation by Hydride Abstraction. In the early 1970s, Barton developed a method for the oxidative hydrolysis of ketals to ketones, e.g. in the tetracycline series (eq 3). The same conditions can also be used to hydrolyze thioketals. Acetonides of... 

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