Isocampholenic Acid Derivatives as Potential Fragrances

(+)-Isocampholenic acid, prepared in two steps from (1<i>S</i>)-(+)-10-camphorsulfonic acid in 60% yield (on a scale of 172 mmol), served as the starting compound for the synthesis of small libraries of isocampholenic acid derivatives, comprising a total of 60 compounds, which are of interest due to their olfactory properties. Although isocampholenic acid derivatives are thermodynamically up to 5.9 kcal/mol less stable than endocyclic alkene isomers according to DFT calculation, only minor (up to 2%) isomerization to α-campholenic acid isomers was observed in most cases. The products were fully characterized, and their odor properties were preliminarily assessed by untrained laypersons. This study represents the first systematic exploration of the chemical space of isocampholenic acid. Novel derivatives with distinct odor profiles were discovered, and promising directions for future functionalization for fragrance development were identified.