Synthesis and Olfactory Characterization of Sila-Methyl Pamplemousse and Related Odorants with a 2,2,5-Trimethyl-2-silahex-4-ene Skeleton

The synthetic grapefruit odorant methyl pamplemousse (1a) has lately become an important trend odorant, and the related 2,2,5-trimethylhex-4-enes 2a–4a also possess interesting olfactory properties of fresh hesperidic and fruity-agrestic character. On the basis of the carbon/silicon switch strategy, the silicon-containing analogues sila-methyl pamplemousse (1b) and 2b–4b were synthesized and studied for their olfactory properties (olfactory evaluation of the C/Si pairs 1a/1b–4a/4b). Sila substitution (C/Si exchange) was demonstrated to affect the olfactory properties substantially. The C/Si analogues 1a and 1b were found to be genuine grapefruit odorants, with the silicon compound 1b showing additional agrestic facets. As a proof of principle, it was demonstrated that C/Si analogues can display a different mechanism and rate of degradation (degradation studies with 1a and 1b under acidic conditions).