2-Trifluoromethanesulfonyloxyindole-1-carboxylic Acid Ethyl Ester: A Practical Intermediate for the Synthesis of 2-Carbosubstituted Indoles

Abstract

Ready accessible 2-trifluoromethanesulfonyloxyindole-1-carboxylic acid ethyl ester undergoes palladium-catalyzed coupling reactions with different partners giving rise to 2-aryl, heteroaryl, vinyl, allyl, and alkynyl indoles in good to excellent yields.

Key words

indoles - palladium-catalyzed - boronic acids/esters - alkynes - heteroarylzinc chlorides

References

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13

We synthesized the trifluoromethanesulfonic acid 1-trifluoromethanesulfonyl-1H-indol-2-yl ester 3 from 1,3-dihydroindol-2-one(5) in 70% yield following the procedure described by Gribble.⁷ However, 3 is stable only at low temperatures and after reaction with phenylacetylene or with 2-methyl-3-butyn-2-ol under Sonogashira conditions at 60 °C, the corresponding coupled products were isolated in poor yields (31% and 32%, respectively).