Silicon-Based Noncyclic Woody-Ambery Odorants:  Synthesis and Olfactory Characterization of 4,4,6,6-Tetramethylheptan-2-one and Its Sila-Analogues

4,4,6,6-Tetramethylheptan-2-one (Me3C-CH2-CMe2-CH2C(O)Me, 7a) and the three sila-analogues Me3Si-CH2-CMe2-CH2C(O)Me (7b), Me3C-CH2-SiMe2-CH2C(O)Me (7c), and Me3Si-CH2-SiMe2-CH2C(O)Me (7d) were synthesized and studied for their olfactory properties and vapor pressures. While the parent carbon compound 7a has a powerful woody-ambery odor reminiscent of Kohinool (3) with a camphoraceous-aromatic side, the 6-sila-analogue 7b is similar in tonality with a fatty and more pronounced camphoraceous side. The camphor note increases even further for the intense 4-sila-analogue 7c and dominates the odor profile of the 4,6-disila-analogue 7d, which displays additional earthy and green-fruity facets. In terms of odor values and threshold values, compound 7d is the most powerful, albeit the least woody-ambery compound. Concerning the vapor pressure, it constitutes the least volatile of the series studied; interestingly, the vapor pressure of 7b is almost twice as high as that of 7c.