Abstract
Two seco-theaspiranes with pronounced blackcurrant notes, 2-tert-butyl-5-methyl-2-propyl-2,5-dihydrofuran (7) and 2-tert-butyl-5-methyl-2-propyltetrahydrofuran (8), were synthesized by a synthetic sequence consisting of Grignard reaction, Lindlar hydrogenation, and cyclization followed by optional Pd-catalyzed hydrogenation. The sequence was modified for the synthesis of the oxygenated analogs 2-(2′-tert-butyl-5′-methyltetrahydrofuran-2′-yl)propan-2-ol (9) and 3-(2′-tert-butyl-5′-methyltetrahydrofuran-2′-yl)butan-2-one (10). The first modification featured trimethylsilyl ether protection and stepwise construction of the alkyne moiety necessitated by steric hindrance. In the second modification, a but-2-en-2-yl group was utilized as latent 3-hydroxybut-1-en-2-yl functionality, and the steric constraint around the tertiary hydroxy group was exploited to introduce a stereocenter by SN2 ring closure. As for the parent compounds 7 and 9, the odor of the oxygenated seco-theaspiranes was shifted towards a woody tonality. The like-diastereomer 9a even had a typical patchouli profile, and the enantiomers 10a and 10b differed significantly in their olfactory properties.
Key words
furans - Grignard reactions - natural products - odorants -
seco-structures
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