Reactions and characterization of allylic and related zirconium reagents (allenic and γ-alkoxyallylic zirconiums) generated by treatment of allylic and/or propargylic ethers with a zirconocene-butene complex (“Cp2Zr”) are described.
Preparation and regio- and diastereoselective reactions of allylic zirconium reagents from allylic ether derivatives
作者:Hisanaka Ito、Takeo Taguchi、Yuji Hanzawa
DOI:10.1016/s0040-4039(00)91605-8
日期:1992.3
Allylic zirconium reagents were generated by treating allylic ether derivatives with zirconocene “Cp2Zr”. The allylic zirconium reagents reacted with aldehydes in highly regio- and diastereoselective manner to give homoallylicalcohol compounds.
Aliphatic aldehydes react with catalytic amount of Dibal-H in n-pentane to give the corresponding Tishchenko products in good to excellent yields. On contrary, α-silyloxy aldehydes give α-silyloxy ketones via Oppenauer oxidation under similar condition. Tishchenko reaction of ω-alkene aldehydes followed by RCM and hydrogenation affords a convenient method to prepare the 11–37 membered macrocyclic lactones
Synthetic applications of the amine-base treatment in the ozonolysis of substituted-allyl silyl ethers or -allyl esters via a novel ene–diol type rearrangement
作者:Yung-Son Hon、Ying-Chieh Wong
DOI:10.1016/j.tetlet.2004.12.135
日期:2005.2
The ozonolysis of substituted-allyl silyl ethers or -allyl esters followed by treatment with bases gave the corresponding α-silyloxy ketones or α-acyloxy ketones in good yields. The reaction is proposed to proceed via a novel ene–diol rearrangement of the corresponding α-silyloxy aldehydes or α-acyloxy aldehydes intermediates.
Nucleophilic additions to and reductiosn of 5-formyl-and 5-acyl-2-isoxazolines (4,5-dihydeoisoxazoles): a stereoselective route to β,γ-dihydroxy ketones
作者:Dennis P. Curran、Jaincun Zhang
DOI:10.1039/p19910002613
日期:——
Reductions of readily available 5-acyl-2-isoxazolines with L-Selectride follow the Felkin-Anh model and produce syn-5-hydroxyalkyl-2-isoxazolines with excellent (> 95:5) selectivities. Swern oxidation of 5-hydroxymethyl-2-isoxazolines, followed by direct addition of a Grignard reagent to the intermediate 5-formyl-2-isoxazolines, also follows the Felkin-Anh model and produces anti-5-hydroxyalkyl-2-isoxazolines with modest (80:20) to excellent (> 95:5) selectivity. In contrast, additions of Grignard reagents to 5-acyl-2-isoxazolines follow the chelation model, and give syn or anti products (depending on choice of acyl substituent and Grignard reagent) with good (90:10) to excellent selectivity. These selectivities are almost always far superior to those that can be obtained by direct nitrile oxide cycloaddition to a chiral allylic alcohol or ether. The resulting products are readily reduced to syn- or anti-beta,gamma-dihydroxy ketones. A speculative model to explain this surprising reversal in selectivity between formyl and acyl isoxazolines is proposed.