Calcium-Mediated Catalytic Synthesis of 1‑(Diorganylamino)-1,4-diphenyl-4-(diphenylphosphanyl)buta-1,3-dienes

The hydroamination
of diphenylbutadiyne with 1 equiv of the secondary
amines HNRR′ (R/R′ = Ph/Ph, Ph/Me, and pTol/Me) in the
presence of catalytic amounts of the tetrakis­(amino)­calciate K2[Ca­{N­(H)­Dipp}4] (Dipp = 2,6-diisopropylphenyl)
yields the corresponding 1-(diorganylamino)-1,4-diphenylbut-1-ene-3-ynes
as a mixture of E/Z isomers. These
tertiary alkenylamines react with diphenylphosphane to form RR′N–C­(Ph)CH–CHC­(Ph)–PPh2 [R/R′ = Ph/Ph (1), Ph/Me (2), and pTol/Me (3)] in the presence of catalytic amounts
of [(THF)4Ca­(PPh2)2] or of the same
calciate K2[Ca­{N­(H)­Dipp}4]. Whereas the hydroamination
is regio- (amino group in 1-position) but not stereoselective (formation
of E and Z isomers), this second
hydrofunctionalization step is regio- (phosphanyl group in 4-position)
and stereoselective (only E isomers are formed),
finally leading to mixtures of (E,E)- and (Z,E)-1-(diorganylamino)-1,4-diphenyl-4-(diphenylphosphanyl)­buta-1,3-dienes.