Synthesis and Olfactory Properties of a 6′‐Silasubstituted “Spiro[4.5]‐δ‐Damascone”

The silicon analogue of the potent spirocyclic δ‐damascone odorant 6 was synthesized from allyltrichlorosilane ( 15 ) and but‐2‐en‐1‐ol ( 16 ). The latter was transformed to 3‐methylpen‐4‐enenitrile ( 11 ) by Saucy–Marbet reaction with ethoxyethane and subsequent treatment with HONH 2 ⋅ HCl. The resulting γ,δ‐unsaturated nitrile 11 was silylated with 1‐allyl‐1‐chlorosilolane ( 14 ), which was prepared from allyltrichlorosilane ( 15 ) and the bis‐Grignard reagent of 1,4‐dichlorobutane. Metathetic ring closure employing the Grubbs I catalyst, followed by DIBAL reduction with non‐aqueous work up, Grignard reaction with prop‐1‐en‐1‐ylmagnesium bromide, and Attenburrow MnO 2 oxidation concluded the synthesis. The target compound was found to be olfactorily related to the spiro[4.5]‐δ‐damascone lead, but approximately 900 times weaker. In a type of enol Brook rearrangement, it thermally decomposes however to 3,6‐dihydro‐2 H ‐1,2‐oxasilocine ( 20 ), which surprisingly is a damascone odorant as well; although, 12 000 times weaker.