Novel fragrant aldehydes from (1R,5R)-sabinene: An experimental study supported by DFT calculations revealing an unusual hydroformylation mechanism

The fragrance industry continually searches for compounds that introduce new scent notes or improve existing ones. Herein, we report a methodology for obtaining two novel aldehydes, potentially interesting for application in fragrance formulations, via rhodium-catalyzed hydroformylation of (1R,5R)-sabinene, a biorenewable monoterpene available in many essential oils. One of the aldehydes, which retained the original sabinene skeleton, was derived from the hydroformylation of the exocyclic C-C double bond through the accepted hydroformylation mechanism. The other aldehyde arose from the interaction of rhodium with the cyclopropane ring through an unusual mechanism, which resulted in the cyclopropane ring cleavage, forming a product that shares structural similarities with established fragrant molecules. The selectivity was controlled by adjusting the reaction conditions (temperature, pressure, P-ligand, and P/Rh ratio). Each aldehyde was obtained in a 70–80 % yield, depending on the reaction conditions. Combining our experimental findings with DFT calculations allowed us to propose an unusual hydroformylation reaction mechanism involving cyclopropane moiety in vinylcyclopropanes. [Display omitted] •(1R,5R)-Sabinene is a bio-renewable monoterpene available from essential oils.•ca. 96 % total selectivity for novel aldehydes from sabinene hydroformylation.•Aldehydes regioselectivity was controlled by adjustment in reaction conditions.•An unusual mechanistic route was proposed and supported by DFT calculations.•The aldehyde products are potentially useful as fragrances ingredients.