Synthesis 2021; 53(04): 765-774
DOI: 10.1055/s-0040-1705958
paper

Reaction of Lithiated Propargyl Ethers with Carbonyl Compounds – A Regioselective Route to Furan Derivatives

Igor Linder
,
Robby Klemme
,
This work was supported by the Deutsche Forschungsgemeinschaft.


Abstract

The deprotonation of 3-aryl-substituted alkyl propargyl ethers with n-butyllithium provides an ambident anion that reacts with carbonyl compounds to provide mixtures of γ-substituted products with alkoxyallene substructure and of α-substituted propargyl ethers. The ratio of the two product types strongly depends on the solvent: in diethyl ether the γ-substituted products predominate whereas the more polar tetrahydrofuran favors the α-adducts. The primary addition products undergo 5-endo-trig or 5-endo-dig cyclizations under various reaction conditions to afford isomeric furan derivatives. The highest selectivity in favor of α-substituted products was achieved by employing a MOM-protected propargyl ether. During the protonation step no evidence for a proton shift leading to an isomeric allenyl anion was found. A brief mechanistic discussion tries to rationalize the observed regio­selectivities.

Supporting Information



Publikationsverlauf

Eingereicht: 20. August 2020

Angenommen nach Revision: 26. September 2020

Artikel online veröffentlicht:
28. Oktober 2020

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