Kinetic and thermodynamic control in the lithiation of 2,6-dimethylchromone, and selective lithiations in 2-(x-furyl)chromones and in furanochromones related to khellin
作者:Anna M. B. S. R. C. S. Costa、Francis M. Dean、Michael A. Jones、Dennis A. Smith
DOI:10.1039/p19860001707
日期:——
The addition of 2,6-dimethylchromone to lithium di-isopropylamide (LDA) allows formation, under thermodynamiccontrol, of the 2-methylene carbanion (3), but this seems to react at the carbonyl oxygen atom with carbon dioxide so no carboxylic acid can be isolated. With ethyl chloroformate (but not diethyl carbonate) this carbanion does afford the expected ethyl chromon-2-ylacetate (1d). The chromonylacetic
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
作者:Ana M. B. S. R. C. S. Costa、Francis M. Dean、Michael A. Jones、Dennis A. Smith、Rajender S. Varma
DOI:10.1039/c39800001224
日期:——
Lithiumdi-isopropylamide at –70 °C can remove the α-proton frombenzofuran 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-dimethylchromoneβ-deprotonation is kinetically favoured allowing 3-acylation to be