Mechanistic pathways in CF3COOH-mediated deacetalization reactions.

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 mole...