Hydrolysis of enol ethers

Reaction of 1-ethoxycyclohexene (34) with dichlorocarbene gives 1-ethoxy-7,7-dichloronorcarane (35) in 87 % yield. Rearrangement of dichlorocyclo-propane (35) in hot quinoline results in loss of both chlorine atoms to give l-ethoxycyclohepta-l,3,5-triene (37) in 37% yield. Hydrolysis of enol ether (37) with a very small quantity of hydrochloric acid in methanol produces cyclohepta-3,5-dienone (38) in 91 % yield. ... 

The acid-catalyzed hydrolysis of enol esters (RCOOCR =CR) can take place either by the normal Aac2 mechanism or by a mechanism involving initial protonation on the double-bond carbon, similar to the mechanism for the hydrolysis of enol ethers given in 10-6, ° depending on reaction conditions. In either case, the products are the carboxylic acid RCOOH and the aldehyde or ketone R2" CHCOR. ... 

Hydrolysis of enol ethers, acetals, or ortho esters... 

A selective heating in liquid/liquid systems was exploited by Strauss and coworkers in a Hofmann elimination reaction using a two-phase water/chloroform system (Fig. 2.10) [32]. The temperatures of the aqueous and organic phases under micro-wave irradiation were 110 and 55 °C, respectively, due to the different dielectric properties of the solvents (Table 2.3). This temperature differential prevented decomposition of the final product. Comparable conditions would be difficult to obtain using traditional heating methods. A similar effect has been observed by Hallberg and coworkers in the preparation of /3,/3-diarylated aldehydes by hydrolysis of enol ethers in a two-phase toluene/aqueous hydrochloric acid system [33],... 

Hydrolysis of alkyl halides 0-4 Hydrolysis of inorganic esters 0-6 Hydrolysis of enol ethers, acetals, or ortho esters... 

Deuterium solvent IE in the antibody catalysed hydrolysis of enol ethers... 

Hydrolysis of enol ether with aqueous acid... 

Alkylation of potassium enolates is not always fruitful, and so counterion exchange with lithium bromide prior to addition of the electrophile has been recommended. Reduction of aromatic esters instead of acids provides a number of potential advantages. The esters tend to be more soluble than carboxylate salts, hydrogenolysis of 2-alkoxy substituents does not appear to present the s me problem, and the products are more stable. This can be important when enol ether functions are generated, allowing the necessarily acidic work-up procedures for carboxylic acids to be avoided. Indeed, the hydrolysis of enol ether functions may be very slow in aqueous acid and is best achieved through catalysis by mercury(II) nitrate. ... 

The enantioface selective protonation of prochiral enol derivatives is a simple and attractive route for the preparation of optically active carbonyl derivatives. Reports of stoichiometric protonation of metal enolates by a chiral proton source at low temperature leads to optical yields from 20 to 85% ee and yeast esterase catalyzes the hydrolysis of 1-acetoxycycloalkenes with enantioselectivi-ties between 41 and 96% for enol protonation [17,18]. These reactions involve enolates under basic conditions. Hydrolysis of enol ethers under acidic conditions proceeds via a rate-determining carbon protonation and is catalyzed by carboxylic acids [19,20]. Raymond et al. [21] reasoned that a complementary... 

General acid-base catalysis is defined experimentally by the appearance in the rate law of acids and/or bases other than lyonium or lyate ions. For example, the hydrolysis of enol ethers 1.2 (Scheme 2.2) is general acid-catalyzed. In strong acid the rate expression will be the same as in Scheme 2.1, but near neutral pH the rate is found to depend also on the concentration of the buffer (HA + A ) used to maintain the pH. Measurements at different buffer ratios show that the catalytic species is the acid HA. (If more than one acid is present there will be an additional term kHAi[HA ][1.2] for each.)... 

Scheme 8.47. A pathway for the acid-catalyzed hydrolysis of enol ethers.

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