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J. Cosmet. Sci., 49, 299-308 (September/October 1998) Synthesis and odor characteristics of isomeric 3,3,7-trimethyl-4-octen-'l-ols and their 3-sila analogues ROBERT OBARA and CZESLAW WAWRZEI•ICZYK, Institute of Chemistry, Pedagogical University, Chfcidska 5, 25-020 Kielce (R. 0.), and Department of Chemistry, Agricultural University, Norwida 25, 50-375 Wroctaw (C.W.), Poland. Accepted for publication August 31, 1998. Synopsis The isomeric (E) and (Z) 3,3,7-trimethyl-4-octen-l-ols and their 3-sila analogues were synthesized. The (Z) 3,3,7-trimethyl-4-octen-l-ol was obtained by the isomerization of E alcohol via its epoxide deoxygenation according to the Vedejs method. Both sila analogues were synthesized from 4-methyl-l-pentyne. The carbon chain was elongated by alkyne silylation with dimethylvinylchlorosilane (synthesis of Z isomer) or by hydrosilylation with dimethylchlorosilane followed by Reformatsky reaction with ethyl bromoacetate (syn- thesis of isomer E). Odors of alcohols obtained and their acetates have been also evaluated. The odors of carbon compounds are more intense and more fresh than their silicon analogues. INTRODUCTION Naturally occurring acyclic monoterpene alcohols are used in many fragrance composi- tions because of their pleasant and original odors. Synthesized by us, 3,7-dimethyl-4- octen-l-ol, the structural analogue of citronellol (1), and its homologue with an addi- tional methyl group at C-7 are also characterized by pleasant, floral odors (2). The 7-sila analogue of the last alcohol was also obtained. One of the reasons for our interest in the synthesis of silaisoprenoid compounds are studies on the influence of the presence of silicon in the molecule on the biological activity or odoriferous properties of the compound. The influence on biological activity was documented, for example, for sila-antimuscarinic agents (3,4) sila-pyrethroids (5), and sila-juvenoids (6,7). The effect on odoriferous properties of the replacement of the carbon atom with silicon in the molecule has been studied by Wannegat eta/. (8-10). Their interesting results encouraged us in synthesizing acyclic silaisoprenoids. As an extension of our studies, we have synthesized a new homologue of our synthetic terpene alcohol (3,7-dimethyl-4-octen-l-ol), with an additional methyl group at C-3 and its 3-sila analogue. Both alcohols were obtained in pure isomeric (E and Z) forms. RESULTS AND DISCUSSION The (E) isomer of the title compound was obtained in three-step synthesis from 3- 299