Enantiospecific Syntheses of Bicyclic Fragrance Molecules From Verbenone: Enhancing Odour Profiles and Stability

Fragrances derived from terpenoid scaffolds continue to play a central role in the design of synthetic odorants, with trans-fused decalin system providing particularly valuable ambergris like woody notes. Inspired by the structural and stereochemical features of polywood and its analogues, we report herein a concise and versatile synthetic approach to novel bicyclic frameworks from the chiral pool precursor (-)-verbenone. An efficient, enantiospecific synthesis of trans-fused bicyclic fragrance molecules, including nor-polywood and novel ^[6,7]- and ^[6,5]-fused analogues, is reported. This six-step synthetic sequence utilized a powerful combination of conjugate addition, cyclobutane ring-opening, and a key Ring-Closing Metathesis (RCM) reactions. Subsequent stereoselective reductions, acetylations, and hydrogenations yield a diverse range of bicyclic frameworks in good overall yields with excellent stereocontrol. Importantly, olfactory evaluation confirms that all synthesized products retain the characteristic woody, amber-like notes of premium ambergris substitutes. These findings demonstrate the critical influence of ring-size variation on fragrance properties, providing new insights for the rational design of sophisticated odorants. This work not only provides an efficient synthesis of structurally diverse bicyclic systems but also expands the chemical space of ambergris-type odorants, offering new insights into structure-odour relationships for the development of next-generation woody fragrance ingredients.