7622-78-8Relevant academic research and scientific papers
A Concise Approach to Oxo-Dehydrorotenoid by Direct Lactonization and the Total Syntheses of Stemonone, Rotenonone, 6-Oxo-dehydroelliptone, and 6-Oxo-6a,12a-dehydrodeguelin
Boonsombat, Jutatip,Thongnest, Sanit,Ruchirawat, Somsak
supporting information, p. 2971 - 2983 (2019/03/27)
An approach to construct the oxo-dehydrorotenoids via direct lactonization of isoflavone-2-carboxylic acids is reported. The present reaction proceeds smoothly with good substrate scope and an operationally simple protocol. The application of this method
Lithiation in Flavones, Chromones, Coumarins, and Benzofuran Derivatives
Costa, Ana M. B. S. R. C. S.,Dean, Francis M.,Jones, Michael A.,Varma, Rajender S.
, p. 799 - 808 (2007/10/02)
Flavones are lithiated at position 3 by lithium di-isopropylamide in tetrahydrofuran at -78 deg C and the products are stable at that temperature.Appropriate reagents replace the lithium by carboxy, ethoxycarbonyl, mercapto, methylthio, trimethylsilyl, hydroxy, and other groups, sometimes giving products not previously available.Benzofurans are preferentially lithiated at position 2 if this is free, and may not be attacked if it is blocked, but if there is an activating group (i.e., one able to co-ordinate with the lithium cation) at position 2, then lithiation occurs at position 3.In the benzofuran series ring-opening is easier and lithiation often leads directly to acetylenic phenols.Chromones can be lithiated at positions 2 and 3 depending upon the substitution pattern and whether the substituents are activating.Aurones are not easily deprotonated, and only the acetylenic phenol arising from ring opening was found in the one successful case.Coumarins tend to behave simply as esters and give amides with the lithiating reagent, but 4-methoxycoumarin is readily lithiated at position 3.It is suggested that 3-deprotonation in ethers occurs easily only when there is an ether link antiperiplanar to the proton removed, and that the lithiated species are really unstable intermediates in trans-eliminations leading to alkyne derivatives.
β-Deprotonation by Lithium Di-isopropylamide. Vinyl Carbanions from Oxygen Heterocycles in the Synthesis of Carboxylic Acids in the Benzofuran, Flavone, and Coumarin Series and in the Regiospecific Acylation of 2,6-Dimethylchromone
Costa, Ana M. B. S. R. C. S.,Dean, Francis M.,Jones, Michael A.,Smith, Dennis A.,Varma, Rajender S.
, p. 1224 - 1226 (2007/10/02)
Lithium di-isopropylamide at -70 deg C can remove the α-proton from benzofuran in the absence of activating groups and the β-proton if such groups are present; in flavone and 4-methoxycoumarin β-deprotonation occurs readily and the carbanions are easily carboxylated giving acids not previously accessible, while in 2,6-dimethylchromone β-deprotonation is kinetically favoured allowing 3-acylation to be achieved separately from the conventional acylation at the 2-methyl group.
