Optically Active Ionones and Derivatives: Preparation and Olfactory Properties

The isomeric ionones 1−3 are of both academic and commercial interest. Since their first preparation at the end of the 19th century they have been widely used as fragrances and as starting materials or building blocks in the synthesis of many relevant products. The regioselective and/or enantioselective preparation of ionones has therefore been investigated with growing interest over the last decades. In this Microreview, we summarize the syntheses of optically active α- and γ-ionones (1, 3) and the epoxy and dihydro ionones 4−7. In addition, the olfactory properties of most of them are reported comprehensively.