A full account of the Brønsted acidcatalyzed, enantioselective synthesis of 4H-chromenes and 1H-xanthen-1-ones from o-hydroxybenzyl alcohols and β-dicarbonylcompounds is provided. The central step of our strategy is the BINOL–phosphoric acidcatalyzed, enantioselective cycloaddition of β-diketones, β-keto nitriles, and β-keto esters to in situ generated, hydrogen-bonded o-quinone methides. Upon acid-promoted
Synthesis of 2<i>H</i>-Chromenes via Unexpected [4 + 2] Annulation of Alkynyl Thioethers with <i>o</i>-Hydroxybenzyl Alcohols
作者:Hao-Zhen Bu、Hang-Hao Li、Wen-Feng Luo、Chen Luo、Peng-Cheng Qian、Long-Wu Ye
DOI:10.1021/acs.orglett.9b04421
日期:2020.1.17
A novel Brønsted acid-catalyzed reaction of alkynylthioethers with o-hydroxybenzyl alcohols via an unexpected formal [4 + 2] annulation has been developed. This metal-free protocol leads to the facile and practical synthesis of valuable polysubstituted 2H-chromenes in mostly good to excellent yields under mild reaction conditions and features a wide substrate scope and excellent functional group tolerance
Transition‐Metal‐Free [4+3]‐Cycloaddition of
<i>ortho</i>
‐Quinone Methides and Isomünchnones: Catalytic and Diastereoselective Assembly of Oxa‐bridged Oxazocine Scaffolds
between an in situ generated ortho‐quinonemethide and an isomünchnone to yield oxa‐bridged oxazocine cores, generating N2 and H2O as the sole by‐products. Using only catalytic amounts of camphorsulfonic acid, it is possible to generate both reactive intermediates in one step, eliminating the need for rhodium catalysts generally employed for isomünchnone formation. Spectroscopic data and X‐ray crystallography
Organocatalytic Asymmetric [2 + 4] Cycloadditions of 3-Vinylindoles with ortho-Quinone Methides
作者:Si-Jia Liu、Man-Su Tu、Kai-Yue Liu、Jia-Yi Chen、Shao-Fei Ni、Yu-Chen Zhang、Feng Shi
DOI:10.3390/molecules26216751
日期:——
Catalytic asymmetric [2 + 4] cycloadditions of 3-vinylindoles with ortho-quinone methides and their precursors were carried out in the presence of chiral phosphoric acid to afford a series of indole-containing chroman derivatives with structural diversity in overall high yields (up to 98%), good diastereoselectivities (up to 93:7 dr) and moderate to excellent enantioselectivities (up to 98% ee). This