Vinyl- and Divinylcyclopentadienes by Rhodium-Catalyzed Condensation of Alkynes with Cross-Conjugated Amino Metallahexatrienes [= (1-Amino-1,3-butadien-2-yl)carbene Complexes] (M = Cr, W)

We report on the first example of a transition metal-catalyzed cyclization reaction of a Fischer carbene complex. It comprises the generation of vinyl- and divinyl cyclopentadienes under exceedingly mild conditions at 20 °C by condensation of (1-amino-1,3-butadien-2-yl)carbene complexes (= cross-conjugated metallahexatrienes) (CO)5MC(OEt)C(CHNR2)CR1CHR23 (M = Cr, W) with alkynes R3C≡CH 4 (R3 = Ph, cyclohex-1-enyl, isopropenyl, methoxymethyl, 1-trimethylsiloxycyclohex-1-yl) in the presence of catalytic amounts of [(COD)RhCl]2. The starting compounds 3 are accessible in high yields by addition of enamines (E)-R2NCHCHR22 to (1-alkynyl)carbene complexes (CO)5MC(OEt)C≡CR11 (M = Cr, W; R1 = Ph, cyclohex-1-enyl).