Present and future of cyclopropanations in fragrance chemistry

The elaboration of new cyclopropanation methods is expected to make selectively new Δ-compounds available, either as precursors or as new ingredients with superior olfactory impacts. The improvement of cyclopropanation processes through understanding of reaction mechanisms reduces costs and environmental impact. Givaudan is the leading 'Flavor & Frangrance' company which successfully brings Δ-molecules to the market. Javanol(®) , for example, with its unique performance exemplifies the product of an efficient industrial cyclopropanation of a dienol precursor. Serenolide(®) , Toscanol(®) , and Pashminol(®) are other high-impact Δ-fragrance ingredients manufactured at Givaudan. This review describes our journey from advanced SimmonsSmith methodology using Zn carbenoids, to Al- and Mg-mediated cyclopropanation techniques in the context of related alternative cyclopropanation methods for the transfer of the CH2 group onto CC bonds. The resulting cyclopropane products are themselves interesting substrates for further transformation to other flavor and fragrance compounds. Throughout this Review, the notation Δ refers to the presence of a cyclopropane ring, i.e., a 'Δ-compound' is defined as a compound that contains a cyclopropyl substituent or a 'fused cyclopropa' component, or a 'spiro-cyclopropane' moiety.