Design, Synthesis and Olfactory Properties of 2-Substituted 2-<i>tert</i>-Butyl-5-methyl-2,5-dihydrofurans: <i>seco</i>-Derivatives of Theaspiranes
作者:Philip Kraft、Kasim Popaj、Agnese Abate
DOI:10.1055/s-2005-918404
日期:——
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.
具有明显黑加仑香味的两种次级锡兰螺环烷,2-叔丁基-5-甲基-2-丙基-2,5-二氢呋喃(7)和2-叔丁基-5-甲基-2-丙基四氢呋喃(8),通过包括格氏反应、林德拉氢化和环化,随后可选择钯催化的氢化反应的合成序列合成。该序列经过修改,用于合成含氧化合物2-(2'-叔丁基-5'-甲基四氢呋喃-2'-基)丙烷-2-醇(9)和3-(2'-叔丁基-5'-甲基四氢呋喃-2'-基)丁烷-2-酮(10)。第一次修改特色是三甲基硅醚保护以及由于空间位阻所需的乙炔部分的逐步构建。在第二次修改中,使用2-丁烯-2-基作为潜在的3-羟基丁烯-1-烯-2-基功能性,并通过SN2环闭合引入立体中心,利用围绕三级羟基的空间约束。至于母体化合物7和9,含氧次级锡兰螺环烷的香味向木质调性转变。相似的非对映异构体9a甚至具有典型的广藿香特征,而其对映体10a和10b在嗅觉特性上有显著差异。