enone

An enone, also called an α,β-unsaturated carbonyl compound, is a chemical motif in which a carbonyl group is conjugated with a carbon–carbon double bond. The defining structure is typically represented as R-CO-CH=CH-R', though sometimes written as a C=C-C=O sequence. The simplest examples include enones such as methyl vinyl ketone (CH2=CH-CO-CH3) and chalcones (Ph-CO-CH=CH-Ph).

Enones are known for their reactivity in conjugate addition reactions, also called Michael additions, where a nucleophile adds to the β-carbon of the enone (the carbon adjacent to the carbonyl). They can also undergo 1,2-additions to the carbonyl under certain conditions, and participate in various pericyclic processes and cycloadditions. The conjugation between the double bond and the carbonyl modulates both chemical reactivity and physical properties, making enones versatile building blocks in organic synthesis.

Preparation methods commonly involve aldol condensation between a ketone and an aldehyde followed by dehydration to form the α,β-unsaturated carbonyl compound. Enones also arise by oxidation of allylic alcohols or by other condensation routes. Chalcones, a prominent subclass of enones, are widely used as intermediates in pharmaceutical and polymer chemistry.

In nature and industry, enone motifs appear in a range of natural products, flavors, fragrances, and biologically active compounds. Their reactivity enables diverse transformations in synthesis, including conjugate additions, cyclizations, and polymerizations, making them foundational tools in organic chemistry.