5,6-Disubstituted 1,2,3-Trisilaindanes as Silicon Analogues of Phantolide-Type Musk Odorants: Synthesis, Structure, Reactivity, and Olfactory Properties

In an extension of earlier studies concerning drugs and odorants based on disila-substituted tetrahydronaphthalene and indane skeletons, such as the musk odorant disila-phantolide (1), 1-(1,1,2,2,3,3,6-heptamethyl-1,2,3-trisilaindan-5-yl)ethanone (methyltrisila-phantolide, 2) and a series of related 5,6-disubstituted 1,2,3-trisilaindanes (3−5) were prepared in multistep syntheses. Compounds 2−5 were characterized by 1H, 11B (5 only), 13C, and 29Si NMR studies. In addition, compounds 3−5 were studied by single-crystal X-ray diffraction. The 1,2,3-trisilaindane skeleton proved to have limited stability toward oxidation agents. The oxidation product 6, a novel 1,3,4-trisilaisochroman system, was isolated and characterized. The trisila-phantolide derivatives 2 and 3 do not display a typical musk odor, but instead possess a slightly creamy-lactonic odor with coumarinic aspects of very weak intensity (odor thresholds, >500 ng L−1 air).