s‑Block-Metal-Mediated Hydroamination of Diphenylbutadiyne
with Primary Arylamines Using a Dipotassium Tetrakis(amino)calciate
Precatalyst
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Abstract
The
hydroamination of diphenylbutadiyne with primary arylamines
requires a reactive catalyst. In the presence of heterobimetallic
K<sub>2</sub>[Ca{N(H)Dipp}<sub>4</sub>] (Dipp = 2,6-diisopropylphenyl)
the performance of this reaction in THF yields 2-<i>tert</i>-butyl-6,7,10,11-tetraphenyl-9<i>H</i>-cyclohepta[<i>c</i>]quinoline (<b>1a</b>) and 2-fluoro-6,7,10,11-tetraphenyl-9<i>H</i>-cyclohepta[<i>c</i>]quinoline (<b>1b</b>) within 3 days at room temperature when 4-<i>tert</i>-butyl-
and 4-fluoroaniline, respectively, have been used. During this catalysis <i>o</i>-CH activation occurs and quinoline derivatives are formed.
Blocking the <i>o</i>-CH positions by methyl groups and
use of 2,4,6-trimethylaniline under similar reaction conditions leads
to the formation of <i>N</i>-mesityl-7-(<i>E</i>)-((mesitylimino)(phenyl)methyl)-2,3,6-triphenylcyclohepta-1,3,6-trienylamine
(<b>2</b>) containing a β-diketimine unit with a N–H···N
hydrogen bridge. NMR experiments with labeled 4-<i>tert</i>-butylaniline verify the transfer of N-bound hydrogen atoms to the
newly formed cycloheptatriene ring. If the s-block-metal-mediated
hydroamination of diphenylbutadiyne is performed in refluxing THF
for 6 days, <i>N-</i>aryl-2,5-diphenylpyrroles <b>3a</b>–<b>d</b> (<b>3a</b>, R = tBu, R′ = H; <b>3b</b>, R = F, R′ = H; <b>3c</b>, R = R′ =
Me; <b>3d</b>, R = R′ = H) are obtained regardless of
the substitution pattern of the arylamines
