A Novel Approach to Prezizaane Sesquiterpenes

Abstract

Prezizaane sesquiterpenes are an olfactorily interesting class of tricyclic natural products, which occur in some precious perfumery raw materials. These compounds are biosynthetically derived from farnesyl pyrophosphate via cyclization, but some questions regarding the stereoselectivity of this process have not yet been answered. We discuss a novel and concise access to the tricyclic framework of these sesquiterpenes, as exemplified by the synthesis of (AE)-5-epi-sesquithuriferone (5-epi-4).Introduction. ± In the family of woody, ambery, and balsamic odorants, sesquiterpenoids play an important role in the fragrance industry [1]. Irrespective of a few exceptions, sesquiterpenes are not used in pure form, but as essential oils, which usually are complex mixtures. In most cases, minor constituents contribute olfactorily to the complexity, strength, volume, and substantivity, hence to the beauty of these natural scents. Several of the most-precious essential oils in perfumery contain a number of minor sesquiterpenic constituents that share the same tricyclo[6.2.1.0 1,5 ]undecane 1 ) skeleton, the so-called prezizaanes. The dextrorotatory prezizaene was first isolated from the vetiver species Vetiveria zizanioides [2]. Later, (À)-prezizanol (1) and related compounds were found in Eremophila georgei Diels, a kind of sandalwood [3]. (À)-Jinkohol (2) was isolated from agarwood (Aquilaria malaccensis Benth.) [4] in 1981; its structure was corrected only recently [5]. During the last decade, more than 15 epimeric and enantiomeric prezizaanes were isolated from various natural sources [6], among them ()-prezizaan-7-ol (3) from Haitian vetiver oil [5], the most appreciated vetiver oil in perfumery, and ()-sesquithuriferone (4) as well as (À)-sesquithuriferol (5) from Juniperus thurifera l.[7].2004-1 ) Octahydro-1H-3a,6-methanoazulene (IUPAC name).

Sniffing Out the Sustainable Future: The Renewability Revolution in Fragrance Chemistry**

“…However, the spermotoxicity of these muguet aldehydes could be blocked by the additional “magic methyl” group in Nympheal ( 170 , marked in green, Scheme 20). [160] This methyl group prevents the degradation to its carboxylic acid derivative, and thus the toxification. The retrosynthetic route leads back to the acylated phenol 171 , which is accessible from petrochemical 2‐methoxy toluene ( 172 ) [161,162,163,164] .…”