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1-Metalla-1,3,5-hexatrienes and Related Compounds

“…Intramolecular 4πϩ2π cycloaddition of a 1-metalla-1,3,5-hexatriene insertion of the carbene carbon atom into the α-HC(N) bond of the tertiary amino unit, for bulkier substituents R ϭ Me, Et (Scheme 34). [41] [42] The "molecular switch" of this reaction is based on changes in the (3E/3Z) molecular orientation of the highly congested 6-amino-2-ethoxy-1tungsta-1,3,5-hexatrienes by the bulk of substituents R. [41] Scheme 31. Cyclopenta[b]pyrans by successive insertion of two alkyne units and carbon monoxide into a CrϭC bond…”

“…[41] These compounds metallatrienes (Scheme 44 and 45, path c). underwent π-cyclization at 20°C to form cyclopentadiene derivatives, but on exposure to an excess of (1-alkynyl)carbene complex, gave binuclear compounds, which subsequently were transformed into spiro-tetrahydropyrroles by thermally-induced α-cyclization.…”

Applications of stoichiometric transition metal complexes in organic synthesis

“…Aumann has reported on the use of tungsten carbenes and their reaction with enamines. 34 Reaction of 1-aminocyclohexenes with [(1-alkynyl)carbene] tungsten complexes gave rise to cyclopentadienes and dihydropyrroles.…”

Chromium(0) Alkynylcarbene Complexes as Cβ‐Electrophilic Carbene Equivalents: Regioselective Access to Dienynes and Dienediynes

“…It is well known that the metal alkynyl(alkoxy)carbenes 1 (Scheme 1) readily undergo conjugate nucleophilic addition to form substituted alkenyl(alkoxy)carbenes B via the allenylmetalate species A, [3] and that intermediates containing a metal-carbon single bond, such as metalates, have a high tendency to expel a neutral metal pentacarbonyl fragment. [4] This observation led us to suppose that if a leaving group is adequately placed within the nucleophile moiety, the allenylmetalate A might evolve to enynes C in an overall process that would involve olefination of an sp-hybridized carbon and subsequent carbene rearrangement.…”