acetonide

Acetonide is a cyclic acetal derived from acetone and a vicinal diol. In organic synthesis, it is most commonly encountered as the isopropylidene acetal, a five‑membered ring known as 2,2-dimethyl-1,3-dioxolane, formed when acetone reacts with adjacent hydroxyl groups to protect them during multi-step sequences.

The acetonide ring arises from the condensation of acetone with a 1,2- or 1,3-diol under acid catalysis, with removal of water driving ring closure. The resulting protecting group locks the two hydroxyls in a rigid, cyclic structure that is generally stable to a variety of reaction conditions. The acetonide can be installed selectively on vicinal diols, such as those found in carbohydrate substrates and other polyols.

Applications of acetonides include protection of vicinal diols in carbohydrate chemistry, natural product synthesis, and complex molecule assembly. By masking two adjacent hydroxyl groups, acetonides enable selective reactions at other sites and can improve solubility or crystallinity of intermediates. The choice of acetonide installation conditions and diol selectivity can influence yield and downstream functional group compatibility.

Deprotection of acetonides is typically achieved by acid-catalyzed hydrolysis, often using aqueous acid or buffered conditions. The process regenerates the free diol and releases acetone. While acetonides are generally robust under basic and many neutral environments, they are acid-labile and must be removed when the diol functionality is required in the final product.

Synonyms for the group include isopropylidene acetal and 2,2-dimethyl-1,3-dioxolane. The term acetonide is commonly used in reference to these protecting groups in organic synthesis.