Present and Future of Cyclopropanations in Fragrance Chemistry

AbstractThe elaboration of new cyclopropanation methods is expected to make selectively new Δ‐compoundsavailable, 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.Givaudanis 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®, andPashminol®are other high‐impact Δ‐fragrance ingredients manufactured atGivaudan.This review describes our journey from advancedSimmonsSmithmethodology using Zn carbenoids, to Al‐ and Mg‐mediated cyclopropanation techniques in the context of related alternative cyclopropanation methods for the transfer of the CH2group 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 compo