Organic syntheses via transition metal complexes, C - 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 degr ees C by condensation of (1-amino-1,3-butadien-2-yl)carbene complexes (= cr oss-conjugated metallahexatrienes) (CO)(5)M=C(OEt)C(=CHNR2)CR1=CHR2 3 (M = Cr, W) with alkynes (RC)-C-3=CH 4 (R-3 = 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=CHR2 2 to (1-alkynyl)carbene comp lexes (CO)(5)M=C(OEt)C=CR1 (M = Cr, W; R-1 = Ph, cyclohex-1-enyl).