An Enantiospecific Synthesis of 5-<i>epi</i>-α-Bulnesene

oleh: Jiarui Zong, Jeremy Robertson

Format: Article
Diterbitkan: MDPI AG 2023-05-01

Deskripsi

As a result of its unique fragrance and wider role in traditional medicine, agarwood produced in <i>Aquilaria</i> spp. and certain other trees has been harvested to near extinction as a natural phenomenon. Artificially induced agarwood production in <i>Aquilaria</i> plantations has sated some of the demand although the product quality is variable. Synthetic chemistry may have a role to play in providing sustainable routes to many of the fragrant components identified in agarwood and its smoke when burnt as incense. In this work, we report efforts towards a total synthesis of the guaiane sesquiterpene α-bulnesene, which is found, along with its more fragrant oxidised derivatives, in agarwood. Following the ring-expansion of (<i>R</i>)-carvone using reported procedures, α-butenylation gave a substrate for samarium diiodide mediated reductive cyclisation, the two butenyl epimers of the substrate each leading to a single bicyclic alcohol (<b>24</b> and <b>25</b>). Overall homoconjugate hydride reduction of one of these alcohols was achieved by Lewis acid-mediated ionisation and then hydride transfer from triethylsilane to complete an overall seven-step synthesis of 5-<i>epi</i>-α-bulnesene. This new synthesis paves the way for short routes to both α-bulnesene enantiomers and a study of their aerial and enzymatic oxidation products.