Sila‐α‐galbanone and Analogues: Synthesis and Olfactory Characterization of Silicon‐Containing Derivatives of the Galbanum Odorant α‐Galbanone

Abstract

Silicon compounds 1b–3b are sila‐analogues of the galbanum odorants α‐galbanone (1a), α‐spirogalbanone (2a), and nor‐α‐galbanone (3a), respectively. Sila‐α‐galbanone (1b), sila‐α‐spirogalbanone (2b), and sila‐nor‐α‐galbanone (3b) were synthesized in multistep syntheses in isomerically pure form, starting from Me2SiCl2, (CH2=CH)2SiCl2, and Me2(CH2=CH)SiCl, respectively. Hydroformylation of vinylsilanes, followed by either ring‐closing aldol condensation or ring‐closing alkene metathesis, were the key steps in these syntheses. The C/Si pairs 1a/1b, 2a/2b, and 3a/3b were studied for their olfactory properties. All compounds possess green‐fruity galbanum‐type odors with pineapple aspects and thus are olfactorily related. However, sila‐analogues 1b–3b were found to be weaker than the corresponding parent carbon compounds 1a–3a. This effect is most pronounced for the C/Si pair 2a/2b as indicated by the odor thresholds of 0.023 ng L–1 air (2a) and 3.8 ng L–1 air (2b). However, due to their higher molecular mass, the silicon compounds are less volatile and thus more substantive in functional applications. In contrast to the stable 5‐silacyclohex‐1‐enes 1b and 2b, the 4‐silacyclopent‐1‐ene 3b shows a limited chemical stability. For compound 3a an extremely low odor threshold of 0.0087 ng L–1 air was measured, and the silicon analogue 3b with an odor threshold of 0.085 ng L–1 air is the sila‐odorant with the lowest odor threshold measured so far.

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…A c c e p t e d M a n u s c r i p t 114 diphenyl propargyl alcohol (734), which forms via conversion of the allenylidene intermediate (906) to the acyl complex (907) using water generated in the first step followed by decarbonylation. The iridium carbene complex 924 (Scheme 75) was prepared through treatment of iridium complex 922 with alkyne 923 [1038].…”

Synthesis of Cyclic Fragrances via Transformations of Alkenes, Alkynes and Enynes: Strategies and Recent Progress

“…Besides carbocycles, olefin metathesis can also be used for the construction of other types of rings, using substrates with heteroatom-containing tethers. In 2014, Tacke, Kraft et al reported a Si -heterocyclic fragrance with an intense fruity-green odor and an impressive odor threshold of 0.085 ng/L air, which was the lowest achieved among all the sila-odorants at that time [ 88 ]. The five-membered silacycle was constructed via RCM using the Zhan catalyst, while, formerly, Rh-catalyzed hydroformylation was another key step for simultaneously increasing the carbon chain and introducing a functional group ( Scheme 6 b).…”

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

“…Beyond a few exceptional examples on small rings (damascone and galbanone derivatives) [586,587], the RCM has found more application in the synthesis of macrocyclic musky odorants.…”

“…Beyond a few exceptional examples on small rings (damascone and galbanone derivatives) [ 586 – 587 ], the RCM has found more application in the synthesis of macrocyclic musky odorants. Starting from the natural civettone ( 679 ), muscone ( 680 ), and omega-pentadecalactone ( 681 ), numerous medium size macrocycles have been developed and are now commercially available ( Scheme 162 ).…”