1,4-Dimethyl-2,3-diphenylfulvene: A convenient precursor to heteroatom-substituted-1-methyl-2,5-dimethyl-3,4-diphenylcyclopentadienyl transition metal complexes

Article abstract of DOI:10.1016/0022-328X(95)06083-9

Reaction of 2,5-dimethyl-3,4-diphenylcyclopent-2-enone (1) with Ph₃P=CH₂ in THF gave 2,5-dimethyl-3,4-diphenylcyclopent-2-ene-1-ylidene (2) in 75% yield. Treatment of 2 with one equivalent of Br₂, followed by two equivalents of triethylamine gave 1,4-dimethyl-2,3-diphenylfulvene (3) in 60% overall yield. Treatment of 3 with LiCH₃ and LiC₆H₅ followed by FeCl₂ gave [η⁵-1-CH₃CH₂-2,5-(CH₃)₂-3,4-(C₆H₅)₂C₅]₂Fe and [η⁵-1-C₆H₅CH₂-2,5-(CH₃)₂-3,4-(C₆H₅)₂C₅]₂Fe, respectively, in good yield. Treatment of 3 with LiNHC(CH₃)₃ and LiP(C₆H₅)₂ followed by FeCl₂ gave [η⁵-1-(CH₃)₃CNHCH₂-2,5-(CH₃)₂-3,4-(C₆H₅)₂C₅]₂Fe and [η⁵-1-(C₆H₅)₂PCH₂-2,5-(CH₃)₂-3,4-(C₆H₅)₂C₅]₂Fe, respectively, in good yield. Treatment of 3 with (R)-LiNHCH(CH₃)C₆H₅ followed by FeCl₂ gave the corresponding enantiomerically pure ferrocene complex (R,R)-[η⁵-1-C₆H₅CH(CH₃)NHCH₂-2,5-(CH₃)₂-3,4-(C₆H₅)₂C₅]₂Fe in 44% yield.