Structure — Odor correlation, X. Synthesis and olfactive properties of 7‐oxanorbornanes

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Abstract
The 7‐oxanorbornanes 17–19 are prepared by Diels‐Alder reaction of 2,5‐dimethylfuran (1) and 2‐isopropyl‐5‐methylfuran (2) with 2‐chloro‐ (3) or 2‐acetoxyacrylonitrile (4). The adducts 5–10a,b are hydrogenated (→ 11–16a, b) and subsequently hydrolyzed. From 1 and acrylonitrile (21) the stereoisomers 25a, b can be obtained via 23a, b in various ratios, depending on the reaction conditions. The Grignard reaction of the exo nitrile 25a with MeMgI or iPrMgI gives the exo ketones 27a and 28a. In the case of the endo nitrile 25b the same reaction favors the formation of side products. LiAlH4 reduction of 17, 26b, 27b, and 28a yields the 7‐oxanorbornanyl alcohols 29b–31b and 32a. — The fragrance of the ketones 18 and 19 is very similar to that of the substructures 1,4‐cineol and menthone. The smell of ketones 27 and 28 as well as of the alcohols 29b–31b is weak. Odor quality and strength of the alcohols 32a′, a″ are determined by their ability to form more or less easily an intramolecular hydrogen bond leading to a rigid conformation which is responsible for the typical minty‐camphoraceous odor.