Stereocontrolled [4+1] Annulation of α-Hydroxycyclobutenones: Synthesis of Polysubstituted Cyclopentenones
作者:Xu Mao、Peidong Song、Yu Hao、Zezhong Sun、Xiangdong Hu
DOI:10.1002/adsc.201600670
日期:2016.12.7
A stereocontrolled [4+1] annulation of α‐hydroxycyclobutenones has been disclosed. For the first time, α‐hydroxycyclobutenones have been proven as facile diene precursors for [4+1] annulation. Meanwhile, the reported transformation presents a concise synthetic route to polysubstituted cyclopentenones with high stereoselectivity.
A potentially general regiospecific synthesis of substituted quinones from dimethyl squarate
作者:Leah M. Gayo、Michael P. Winters、Harold W. Moore
DOI:10.1021/jo00051a040
日期:1992.12
A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 3 upon sequential treatment with an organolithium reagent and then BF3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5. Addition of an alkynyl-, alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl- 4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9, and these readily rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene. In a similar fashion, 15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones.
Squarate desymmetrisation–ozonolysis as an approach to β-substituted-α-ketosuccinates and squalestatin synthesis
作者:Herman O. Sintim、Anne Valade、David C. Harling、David M. Hodgson
DOI:10.1016/j.tet.2019.130747
日期:2019.12
Silylated tertiary alcohols from 1,2-addition of alkyllithiums to dialkyl squarates undergo alkene ozonolysis to give beta-substituted-alpha-keto-beta-(silyloxy)succinates. With 3-(triethylsilyloxy)butyllithium the methodology was applied to the 2,8-dioxabicyclo[3.2.1]octane core of the squalestatins. Enantioselective 1,2-addition to di-tert-butyl squarate using butyllithium or diethylzinc/Ti(iPrO)(4) in the presence of chiral ligands (such as bisoxazolines or camphorsulfonamides, respectively) gave the corresponding tertiary alcohols in up to 67.5:32.5 er. (C) 2019 Elsevier Ltd. All rights reserved.