Dedicated to Professor Gerhard Roewer on the occasion of his 70th birthdayIn a recent publication, we reported on the synthesis and olfactory characterization of the four stereoisomers of okoumal (1 a-d) [1] and its silicon analogue disila-okoumal (2 a-d, Scheme 1).[2] All isomers of okoumal (1 a-d) and disila-okoumal (2 a-d) were found to exhibit typical ambery odor notes with woody facets, as is characteristic for the okoumalkaranal family. The configuration at the C-2 stereocenter was, however, found to be of great importance for the odor strength. The lowest odor thresholds were observed for the 2R configured okoumal enantiomers 1 a (0.40 ng L À1 air) and 1 c (0.54 ng L À1 air) and their 2R configured silicon analogues 2 a and 2 c (both 0.31 ng L À1 air).Since the less powerful enantiomers have no negative effect on the overall odor profile, commercial okoumal (1) is manufactured as the isomeric mixture 1 a-d.[3] It was introduced to perfumery by Givaudan as captive in 1992, and has been sold outside since 1999. Okoumal provides significant volume, richness, and warmth to fragrances at low dosage, and prominent examples for the use of 1 in fine fragrances include "Escape for Men" (Calvin Klein, 1993) with 2 % of okoumal and "Fly High Man" (Mexx, 2007) with 1 % of okoumal. It combines especially well with woody odorants, such as cedarwood derivatives, patchouli oil, and sandalwood materials like ebanol [3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol], and its high molecular mass of 288 u (C 19 H 28 O 2 ), coupled with a low vapor pressure, makes okoumal extremely long lasting in applications.The twofold sila substitution of okoumal (1) led to an even higher molecular mass of 320 u (C 17 H 28 O 2 Si 2 ) for disila-okoumal (2), which is very close to the "heaviest" odorant known to date, a linear musk odorant with a molecular mass of 325 u (C 20 H 36 O 3 ). [4,5] The accordingly lower vapor pressure of disila-okoumal led to a clearly weaker odor impression of 2 in comparison with okoumal on the blotter and in applications, despite a slightly better odor threshold of disilaokoumal.To benefit from the positive effect of the disila substitution on the odor threshold, it was desirable to increase the vapor pressure of the disila-okoumal isomers by reducing their molecular mass. For this purpose, the SiÀCH 2 ÀCH 2 ÀSi moiety of disila-okoumal (2) was replaced by the SiÀCH 2 ÀSi and SiÀOÀSi groups, in the hope that this structural modification would not impair the olfactory profile. We report here on the synthesis and olfactory characterization of the disila-okoumal derivatives 4 a-d and 5 a-d (Scheme 2). To get more information about the structure-odor relationships in this class of odorants, the carbon analogues of 4 a-d, compounds 3 a-d (Scheme 2), were also synthesized and analyzed for their olfactory properties. These investigations were performed as part of our systematic studies on sila-substituted odorants.[6] SynthesesThe synthesis of compounds 3 a-d, 4 a-d, and 5 a-d was straightforward. Accor...

In this study, the synthetic potential of the 2,4,6-trimethoxyphenyl (TMOP)-substituted (chloromethyl)silanes (TMOP)Me 2 SiCH 2 Cl (1) and (TMOP) 2 MeSiCH 2 Cl (2) for the preparation of Si-functionalized (silylmethyl)silanes and α,ω-dichlorocarbosilanes (with skeletons consisting of alternate carbon and silicon atoms) was investigated. Compounds 1 and 2 were used as reagents to introduce the ClMe 2 SiCH 2 , MeOMe 2 SiCH 2 , or Cl 2 MeSiCH 2 group by nucleophilic substitution at silicon. The three-step synthetic method involves the (i) transformation of 1 and 2 into (TMOP)Me 2 SiCH 2 MgCl, (TMOP)-Me 2 SiCH 2 Li, (TMOP) 2 MeSiCH 2 MgCl, and (TMOP) 2 MeSiCH 2 Li, respectively, (ii) reaction of these nucleophiles with chloro-or methoxysilanes, and (iii) subsequent selective cleavage of the TMOP protecting group with HCl/Et 2 O or MeOH/[CF 3 COOH]. Using this method, the following compounds were prepared: ClMe 2 SiCH 2 SiMe 3 (3), ClMe 2 SiCH 2 SiMe 2 Cl (4), ClMe 2 SiCH 2 SiMeCl 2 (5), ClMe 2 SiCH 2 SiCl 3 (6), ClMe 2 SiCH 2 Si-(OMe) 3 (7), MeOMe 2 SiCH 2 Si(OMe) 3 (8), Cl 2 MeSiCH 2 SiMe 3 (9), Me 2 Si(CH 2 SiMe 2 Cl) 2 (10), and Me 2 Si-(CH 2 SiMe 2 CH 2 SiMe 2 Cl) 2 (11).

Reaction of the donor-stabilized silylene 1 (which is threecoordinate in the solid state and four-coordinate in solution) with organic 1,3-dienes (2,3-dimethyl-1,3-butadiene, 1,3-butadiene, (E,E)-1,4-diphenyl-1,3-butadiene, 2,3-dibenzyl-1,3-butadiene, 1,3-cyclohexadiene, or cyclooctatetraene) and 1,2-diketones (3,5-di-tert-butyl-1,2-benzoquinone or 1,2-diphenylethane-1,2-dione) leads to the formation of the respective cycloaddition products 2−9. Compounds 2−9 were characterized by crystal structure analyses (7 was studied as the hemi solvate 7·0.5n-C 6 H 14 ) and NMR spectroscopic studies in the solid state and in solution. As the amidinato ligands can switch between a monodentate and bidentate coordination mode, for some of the cycloaddition products studied, the silicon coordination number in the solid state and in solution is different. For example, compound 4 is four-(4a) and six-coordinate (4b) in the solid state (isolated as a 1:1 cocrystallizate of 4a and 4b) and five-coordinate in solution. As demonstrated for the methanolysis of 2 (formation of 10; proof of principle), compounds 2−7 with their reactive Si−N bonds are starting materials for the synthesis of promising mono-and bicyclic organosilicon compounds.

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