Enantiopure Chiral Derivatives of the Fragrance Materials Majantol and Sila-majantol:  A Bioisosteric Carbon/Silicon Switch with Drastic Effects on the Sensory Characteristics

The C/Si analogues 2-methyl-2-(3-methylbenzyl)but-3-en-1-ol (<BO>2a</BO>) and (hydroxymethyl)methyl(3-methylbenzyl)vinylsilane (<BO>2b</BO>) are chiral derivatives of the achiral fragrance materials majantol (<BO>1a</BO>) and sila-majantol (<BO>1b</BO>). Compounds <BO>2a</BO> and <BO>2b</BO> were synthesized as racemates, and the respective (+)- and (−)-enantiomers were obtained by chromatographic resolution (HPLC) of rac-<BO>2a</BO> and rac-<BO>2b</BO> using a chiral stationary phase. The enantiomerically pure compounds (+)-<BO>2a</BO>, (−)-<BO>2a</BO>, (+)-<BO>2b</BO>, and (−)-<BO>2b</BO> (optical rotations determined in methanol) were studied for their sensory properties. Both the odor character and the odor intensity of the silicon compounds (+)-<BO>2b</BO> and (−)-<BO>2b</BO> differ totally from those of the respective carbon analogues (+)-<BO>2a</BO> and (−)-<BO>2a</BO>.