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Hiromichi Fujioka 《Tetrahedron letters》2010,51(15):1945-2017
The first asymmetric total syntheses of the (+)- and (−)-cryptocaryones are described. Removal of the acetal unit of the enone acetal 5, which was obtained in our previous study from the cyclohexadiene acetal 3, afforded the enone acetal 8 in a one-pot procedure. The acylation of 8 with cinnamoyl chloride and subsequent hydrolysis of the resulting acetal gave the lactol 11. Its oxidation with NIS and tetra-n-butylammonium iodide (TBAI) finally furnished the natural (+)-cryptocaryone 2. The same procedure from ent-3 afforded the unnatural one 1. 相似文献
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Fujioka H Sawama Y Kotoku N Ohnaka T Okitsu T Murata N Kubo O Li R Kita Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(36):10225-10238
The concise asymmetric total synthesis of scyphostatin has been achieved by condensation of the optically active cyclohexane unit, prepared from the commercially available 1,4-cyclohexadiene by our own method, and the side chain, prepared by the method developed by Hoye and Tennakoon (T. R. Hoye, M. A. Tennakoon, Org. Lett. 2000, 2, 1481-1483). The modification of the epoxy cyclohexenone unit was achieved in a late stage of the total synthesis, and deprotection of the primary alcohol was conducted in the final step. During the synthesis several key reactions were attained: 1) intramolecular bromoetherification of the cyclohexadiene acetal; 2) stereoselective introduction of the tertiary alcohol, 3) deprotection of the acetal function to the aldehyde by combination with silyl triflate/2,4,6-collidine and the one-pot synthesis of the disilyl aldehyde compounds, with different types of silyl groups, from the dihydroxy acetal compounds; and 4) facile deprotection of the 2,4-dimethoxyphenylmethyl ((2,4)DMPM) protecting group of the primary alcohol. 相似文献
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Frontispiece: Magnesium Lewis Acid Assisted Oxidative Bromoetherification Involving Bromine Transfer from Alkyl Bromides with Aldehydes by Umpolung of Bromide 下载免费PDF全文
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Magnesium Lewis Acid Assisted Oxidative Bromoetherification Involving Bromine Transfer from Alkyl Bromides with Aldehydes by Umpolung of Bromide 下载免费PDF全文
Prof. Dr. Katsuhiko Moriyama Chihiro Nishinohara Prof. Dr. Hideo Togo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(34):11934-11939
An oxidative bromoetherification involving a bromine transfer from alkyl bromides upon reacting them with aldehydes in a Grignard reaction with a concurrent oxidation of bromide was developed to provide substituted tetrahydrofurans in high yields. This reaction, which proceeds through two types of bromine transfer, was promoted by the addition of a Brønsted acid. Mechanistic studies suggested that a magnesium Lewis acid activates hypobromate, which is generated in situ from the reaction of bromide and Oxone to improve the electrophilicity of the bromonium ion (Br+) for the oxidative bromoetherification of alkenyl alcohols. Furthermore, the magnesium Lewis acid catalyzed oxidative bromoetherification of an alkenyl alcohol proceeded to provide a cyclization product in 92 % yield. 相似文献
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