Acetate esters stable

The adamantoate ester is formed selectively from a primary hydroxyl group (e.g., from the 5 -OH in a ribonucleoside) by reaction with adamantoyl chloride, Pyr (20°, 16 h). It is cleaved by alkaline hydrolysis (0.25 N NaOH, 20 min), but is stable to milder alkaline hydrolysis (e.g., NH3, MeOH), conditions that cleave an acetate ester. ... 

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

Many functional groups are stable to alkaline hydrogen peroxide. Acetate esters are usually hydrolyzed under the reaction conditions although methods have been developed to prevent hydrolysis.For the preparation of the 4,5-oxiranes of desoxycorticosterone, hydrocortisone, and cortisone, the alkali-sensitive ketol side chains must be protected with a base-resistant group, e.g., the tetrahydropyranyl ether or the ethylene ketal derivative. Sodium carbonate has been used successfully as a base with unprotected ketol side chains, but it should be noted that some ketols are sensitive to sodium carbonate in the absence of hydrogen peroxide. The spiroketal side chain of the sapogenins is stable to the basic reaction conditions. 

The catalytic activity of rhodium diacetate compounds in the decomposition of diazo compounds was discovered by Teyssie in 1973 [12] for a reaction of ethyl diazoacetate with water, alcohols, and weak acids to give the carbene inserted alcohol, ether, or ester product. This was soon followed by cyclopropanation. Rhodium(II) acetates form stable dimeric complexes containing four bridging carboxylates and a rhodium-rhodium bond (Figure 17.8). 

Despite the presence of two, relatively weak, N—O bonds ( 53 kcal/mol) (255) nitroso acetals are stable under neutral conditions. Therefore, a number of transformations can be performed on the periphery of the cycloadducts without effecting the nitroso acetal. These include both oxidation of alcohols, dihydroxyla-tion of alkenes (247,248,256), Tamao-Heming type oxidation (248-250), reductions of ketones and esters (244,257-261), silylation and desilylation (247,257, 260), and activation with a variety of sulfonylating agents (247,248,257-260). 

Reactions conducted in molten quaternary phosphonium salts require no other solvent (199). This material serves as both promoter and reaction medium. Care must be exercised in choosing the salt in such a reaction, since any decomposition could lead to products such as trialkylphosphines and alkyl halides which are expected to be deleterious to catalyst performance. Tetrabutylphosphonium bromide is reported to provide a stable catalyst medium which can be recycled (199, 200), but other related salts show evidence of thermal decomposition during catalytic reactions. Experiments in tetrabutylphosphonium acetate, for example, are found to produce large amounts of methyl and ethylene glycol acetate esters (199). 

The tinctura iodi of the British Pharmacopoeia is a soln. of half an ounce of iodine, and a quarter of an ounce of potassium iodide in a pint of rectified spirit. P. Wantig found the mol. ht. of soln. —1 941 Cals., and S. U. Pickering —1 714 per 880 mol. of ethyl alcohol. C. Lowig found that alcoholic tincture of bromine is slowly decomposed in darkness, rapidly in light. Alcoholic soln. of iodine, according to H. E. Barnard, are stable in light and in darkness, but according to J. M. Eder they decompose 1000 times more slowly than chlorine water under similar conditions T. Budde has shown that hydriodic acid, acetic ester, and aldehyde are formed, and the electrical conductivity of the soln. increases. J. H. Mathews and E. H. Archibald and W. A. Patrick found a freshly prepared AT-soln. to have an electrical conductivity of 2 4 XlO-6 reciprocal ohms and a sat. soln., 1 61 X10 4 reciprocal ohms at 25°. The decomposition is accelerated by the presence of platinum. The heat of soln. decreases with concentration from —7 92 to —7 42 cals, respectively for dilute and sat. soln. in methyl alcohol, and likewise from —4 88 to —5 22 cals, for similar soln. in ethyl alcohol. The solubility of iodine in aq. soln. of propyl alcohol is not very different from that in ethyl alcohol. 

Vinyl ethers undergo all of the expected reactions of olefinic compounds plus a number of other reactions. For example, vinyl ethers react with alcohols give acetals. The acetals are stable under neutral or alkaline conditions and are easily hydrolyzed with dilute acid after other desired reactions have occurred. Reaction of a vinyl ether with water gives acetaldehyde and the corresponding alcohol and reaction of vinyl ethers with carboxylic acids gives 1-alkoxyethyl esters and with thiols gives thioacetals. 

The first step puts the protecting group on to the (more electrophilic) ketone carbonyl, making it no longer reactive towards nucleophilic addition. The Grignard then adds to the ester, and finally a deprotection step, acid-catalysed hydrolysis of the acetal, gives us back the ketone. An acetal is an ideal choice here—acetals are stable to base (the conditions of the reaction we want to do), but are readily cleaved in acid. 

Through this study we suggest a useful synthetic procedure for good candidate compounds of a new cage-cluster. The ort/io-carboranes are very stable chemicals in this research. Carboranyl acetic ester can be easily introduced to the ortho- carborane skeleton and then many types of cyclisation of carboranyl cluster can be made to occur. The reactivity and reaction mechanism for cyclisation of carborane cluster have been discussed. The mechanisms for boron cluster expansion reaction and cyclisation at carboranyl edge are summarized as follows. 

The last step of this problem is the final cleavage of the two remaining secondary TBS-ethers. This is accomplished by HF-pyridine in THF and addition of hexafluorosilic acid. This significantly facilitates the cleavage of both TBS-ethers in terms of reaction time and yield. Furthermore, the reaction becomes less sensitive to the quality of the HF-pyridine batches. The conditions used are mild enough to allow the presence of acetals, esters and epoxides. Therefore the macrolactone is stable under these conditions, because the pH of hexafluorosilic acid is nearly the same as a solution of HF. Product 19 is itself an epothilone D analogue. 

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