- Mechanistic pathways in CF3COOH-mediated deacetalization reactions
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(Chemical Equation Presented) It has been widely accepted that both the protection of carbonyls and the deprotection of acetals and ketals involve the participation of a water molecule: formation of acetals and ketals is a dehydration process, whereas the deprotection is often referred to as hydrolysis, which, as implied by its name, always requires the presence of water. Herein, we report experimental evidence and mechanistic investigations that provide an alternative view to this process. We have demonstrated that water is not required to convert acetals and ketals to the corresponding carbonyls. The 1H NMR experimental results revealed that the TFA-mediated transformation of acetal to aldehyde occurs via a hemiacetal TFA ester intermediate, which differentiates itself from the classic acid-catalyzed hydrolysis, where the hemiacetal is the putative intermediate responsible for the formation of the aldehyde. More interestingly, alcohols are not the final byproducts as they are in the classical hydrolysis, rather, the two alcohol molecules are converted to two TFA esters under the reaction conditions. On the basis of theNMRevidence, we have proposed that the two TFA esters are formed in two separate steps via a different mechanism along the reaction pathway. Formation of the TFA esters renders the reaction irreversible. To the best of our knowledge, the cascade reaction pathway presented by the TFA-mediated conversion of acetals and ketals to carbonyls has never been previously postulated.
- Li, Wei,Li, Jianchang,Wu, Yuchuan,Fuller, Nathan,Markus, Michelle A.
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supporting information; scheme or table
p. 1077 - 1086
(2010/04/04)
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- NUCLEOPHILIC CHARACTERISTICS OF NUCLEOFUGIC ANIONS IN THE CLEAVAGE OF EPOXIDES BY PROTIC ACIDS AND NITRONIUM FLUOROBORATE
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The cleavage of ethylene, propylene, and cyclohexene oxides by protic acids RCOOH (R= CH3, CF3) in the presence of sources of nucleophilic anions (the lithium or tetrabutylammonium salts of perchloric or substituted sulfonic acids) leads to the formation not only of 2-hydroxyalkyl carboxylates but also of significant amounts of 2-hydroxyalkyl perchlorates and sulfonates.In the reactions of the same oxides with nitronium fluoroborate and the above-mentioned salts in methylene chloride 2-perchloryl- and 2-sulfonyloxyalkyl nitrates are formed with high yields; these are the products from opening of the epoxide ring and subsequent combination of the perchlorate and substituted sulfonate ions.The investigated processes extend the range of reactions involving the concurrent combination of nucleofugic anions and can be used as a method for the production of β-hydroxy- and β-nitroxyalkyl perchlorates and sulfonates.
- Zefirov, N. S.,Kirin, V. N.,Yur'eva, N. M.,Zhdankin, V. V.,Kozmin, A. S.
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p. 1264 - 1279
(2007/10/02)
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