Abstract
Background: Propargylic derivatives are important reagents and building blocks in organic synthesis. They can be obtained starting with propargylic alcohols or their protected forms. The actual methods rely on the use of acidic or metal-catalyzed approachs. These efficient methods however need to use solvents and metals, that are sometimes toxic or expensive. Ways to prepare those derivatives without metals or solvents can thus be an interesting alternative.
Methods: During our work on propargyl carbonates, we found out that reflux in an alcoholic solvent was producing in part the corresponding ether. In this paper we present the study of reaction conditions under microwaves in order to accelerate them. The reaction conditions were optimized using a model substrate and alcohol in order to find the best ratio, temperature and power mode to obtain propargylic ethers form their methyl carbonate. The conditions were then applied to different propargylic derivatives to evaluate the scope of this reaction. Results: The reaction was applied to different propargyl methyl carbonates and alcohols to evaluate the scope of the reaction. Propargyl ethers can be synthesized from carbonates bearing an aromatic ring and alcohols in good yields, by irradiating them together by microwaves. The limitations include hindered alcohols and propargyl carbonates without aromatic rings as substituents on the carbon atom bearing the carbonate. Conclusion: During this study, we were able to find out conditions to prepare propargylic ethers from propargyl carbonate and the alcohol, as a solvent and reagent. The ethers can be easily and readily prepared in 0.5 h by microwave irradiation. The reaction can be applied to derivatives bearing groups that can stabilize the carbocationic intermediate proposed in the mechanism. Even if some limitations were encountered, the reaction gives the opportunity to prepare propargylic ethers from their carbonates without the use of acidic- or metal-catalyzed conditions, or solvent other than the reagents, in a simple and straightforward approach.Keywords: Alcohols, catalyst-free, microwaves, propargylic carbonate, propargylic ethers, solvent-free.
Graphical Abstract
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