s‑Block-Metal-Mediated Hydroamination of Diphenylbutadiyne with Primary Arylamines Using a Dipotassium Tetrakis(amino)calciate Precatalyst

The
hydroamination of diphenylbutadiyne with primary arylamines
requires a reactive catalyst. In the presence of heterobimetallic
K2[Ca­{N­(H)­Dipp}4] (Dipp = 2,6-diisopropylphenyl)
the performance of this reaction in THF yields 2-tert-butyl-6,7,10,11-tetraphenyl-9H-cyclohepta­[c]­quinoline (1a) and 2-fluoro-6,7,10,11-tetraphenyl-9H-cyclohepta­[c]­quinoline (1b) within 3 days at room temperature when 4-tert-butyl-
and 4-fluoroaniline, respectively, have been used. During this catalysis o-CH activation occurs and quinoline derivatives are formed.
Blocking the o-CH positions by methyl groups and
use of 2,4,6-trimethylaniline under similar reaction conditions leads
to the formation of N-mesityl-7-(E)-((mesitylimino)­(phenyl)­methyl)-2,3,6-triphenylcyclohepta-1,3,6-trienylamine
(2) containing a β-diketimine unit with a N–H···N
hydrogen bridge. NMR experiments with labeled 4-tert-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, N-aryl-2,5-diphenylpyrroles 3a–d (3a, R = tBu, R′ = H; 3b, R = F, R′ = H; 3c, R = R′ =
Me; 3d, R = R′ = H) are obtained regardless of
the substitution pattern of the arylamines.