2,3-Epoxygeraniol undergoes dissimilar rearrangements in contact with liquid superacids at low temperature or on solid superacids at room temperature due to different location of the arising cationic center depending on the superacid character. 2,3-Epoxynerol, 6,7-epoxycitronellol, and 6,7-geranyl acetate on ZrO2SO42 afford the corresponding ketones via epoxy ring opening followed by 1,2-hydride shift. With 6,7-geranyl acetate 7-oxanobornane formed as a minor product. The mode of generation of the cationic center (either the olefin protonation or the epoxy ring opening) affects the rearrangement direction at similar conditions.
Studies towards the Taming of the ‘Carbocation’ in the Regioselective Ring Opening of Epoxides to Allylic Alcohols
作者:William Motherwell、Helen Chapman、Karim Herbal
DOI:10.1055/s-0029-1219373
日期:2010.3
Regioselective isomerisation of epoxides to allylic alcohols can be achieved using p-toluenesulfonic acid in the presence of 1,3-dimethylimidazolidin-2-one.
Alternative Synthesis of the Colorado Potato Beetle Pheromone
作者:Juan A. Faraldos、Robert M. Coates、José-Luis Giner
DOI:10.1021/jo4017056
日期:2013.10.18
involves a 6-endo epoxide ring-opening with ester participation that simultaneously inverts the 3R-configuration of the (3R)-2,3-epoxy-2-fluoroprenyl acetate intermediate and installs the ketone functionality of the semiochemical. Extensive NMR studies validate the proposed 6-endo mechanism of the featured rearrangement, which under anhydrous conditions resulted in the formation of two bicyclic 1,3-dioxan-5-ones
雄性科罗拉多马铃薯甲虫分泌的信息素的简明制剂[即。(3 S )-1,3-二羟基-3,7-二甲基-6-辛烯-2-one]从2-氟橙花醇或2-氟香叶醇开始,分四步完成。合成中的关键步骤涉及酯参与的 6-内环氧化物开环,同时反转(3 R )-2,3-环氧-2-氟异戊二烯乙酸酯中间体的 3 R-构型并安装符号化学。广泛的 NMR 研究验证了所提出的特征重排的 6-endo 机制,该机制在无水条件下通过前所未有的分子内 Prins 环化形成两个双环 1,3-二恶烷-5-酮。