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

Abstract

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.