Novel silicon-based patchouli odorants of the trialkyl(1-hydroxy-1-methylethyl)silane type: design, synthesis, and olfactory properties.

tert-Butyl(1-hydroxy-1-methylethyl)dimethylsilane (5), a sila-substituted seco derivative of the recently reported patchouli lead structure (4aR*,8aR*)-1,1,8a-trimethyldecahydronaphthalene-4a-ol (4), and a number of related trialkyl(1-hydroxy-1-methylethyl)silanes and further derivatives, compounds 8-24, with different silicon-bound substituents (Me, Et, iPr, cPr, tBu, iBu, cPent, vinyl, SiMe(3)) were synthesized and studied for their olfactory properties. All of the silanes studied exhibit at least one of the main patchouli odor descriptors 'woody,' 'earthy,' and 'camphoraceous,' and some even exhibit all of them. The silanes MeR(2)SiC(OH)Me(2) (12) and R(3)SiC(OH)Me(2) (14) (R=cyclopropyl) were found to resemble natural patchouli oil most closely, with an even lower odor threshold than the natural lead structure (-)-patchoulol (1). To complete this structure-odor relationship study, the carbon analogues of 12 and 14 (Si/C exchange) were also prepared and characterized. Although they show similar olfactory properties to the silanes 12 and 14, the synthesis of the corresponding carbon analogues is far less straightforward than that of the silicon compounds, and only silanes 12 and 14 can be economically produced industrially.