Palladium-Catalyzed Heterannulation Synthesis of 3-Borylated Indoles

Significance

Reported is the synthesis of indole-3-boropinacolates 2 via a palladium-catalyzed ­borylative cyclization of 2-alkynylanilines 1. N-Sulfonyl anilines (R^³ = SO₂R) were found to be suitable substrates, although N-Boc and N-benzyl anilines failed. Alkyl and aryl alkynes were both well tolerated. The synthesis of 7-azaindole-3-boropinacolate 3 was also reported. A one-pot cyclization/Suzuki-Miyaura cross-coupling procedure delivered biaryl 4, a core fragment of the natural product fluvastatin. Further derivatization of indoles 2 was accomplished via copper-catalyzed azido deboronation to efficiently give 5, which was shown to undergo [3+2] cycloaddition to give 6 in excellent yields.