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Published on: August 16, 2018
Gold(I)-Catalyzed Intermolecular Formal [4+2] Cycloaddition of O-Aryl Ynol Ethers and Enol Ethers: Synthesis of
Tatiana Suárez-Rodríguez1, Ángel L Suárez-Sobrino1, Alfredo Ballesteros1
1Departamento de Química Orgánica e Inorgánica, Instituto de Química Organometálica "Enrique Moles", Universidad de Oviedo, Julián Clavería, Oviedo, 8, 33006-Oviedo, Spain.
Abstract:
Gold(I)-catalyzed formal [4+2] cycloaddition of O-aryl ynol ethers 1 and enol ethers 2 is described. This intermolecular reaction between two electron-rich unsaturated systems takes place, under mild conditions, in the presence of 5 mol% [IPrAu(CH3 CN)]SbF6 as catalyst giving chromene derivatives with good yields. The cycloaddition is completely regio- and stereoselective, as well as versatile for both reactives. Silyl enol ethers can also react in the same way and under the same reaction conditions with quantitative yields. A plausible mechanism through a selective addition of the enol ether to the alkyne gold activated complex followed by an intramolecular aromatic electrophilic substitution is proposed. Several experimental results support the presence of a cationic oxonium intermediate prior to the aromatic substitution. The reaction represents a new entry to the chromene core.
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