Atom Efficient Magnesiation of N-Substituted Alkyl Indoles with a Mixed Sodium-Magnesium Base

This study presents the alkali metal mediated magnesiation (AMMMg) of three N-alkylated indoles with the mixed Na/Mg base [(TMEDA)Na(TMP)₂Mg(CH₂SiMe₃)] 1 (TMEDA = N,N,N′,N′-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidine). All three magnesiated indoles have been successfully characterised by single-crystal X-ray diffraction and solution state NMR studies, whereas iodolysis and Pd-catalysed cross coupling have been investigated. The steric nature of the N-alkyl group changes the reactivity and efficiency of 1 to give either atom efficient disodium tetraindol-2-ylmagnesiates [(Na-TMEDA)₂Mg(α-C₉H₈N)₄] 2 and [(Na-TMEDA)₂Mg(α-C₁₀H₁₁N)₄] 3, or [(TMEDA)Na(TMP)(α-C₁₁H₁₂N)Mg(TMP)] 4, whereby only one indole molecule is selectively deprotonated.