Conjugate addition of enolate anions to vinylcarbene complexes

Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

“…Behavior of 1d toward pyridine was investigated, since the latter is known to displace carbene ligand from its complexes [24,25]; for example, reaction between (CO) 5 Cr@C(OMe)(CHRR 0 ) and pyridine produces (CO) 5 Cr(py) and (MeO)CH@CRR 0 , where shift of hydrogen occurred to the adjacent carbon atom [24]. Heating a solution of 1d in pyridine at 78-80°C for 2 days afforded after workup a green solid, (CO) 3 -(py)Re(j 2 -OC(OMe)C(CH@CEt 2 )C(OEt)) (4), in 69% yield (cf.…”

“…Substitution of a carbonyl ligand by pyridine yields 4. Precedence exists in the literature for pyridine-promoted deprotonation of a carbene ligand and reprotonation at adjacent carbon atom [24,25], presumably by intermediacy of a metal hydrido complex. The step in Scheme 5 involving rotation about the C-C bond is driven by the formation of a stable 5-membered rhenafuran ring, a process proposed for a similar ruthenium system [27].…”

Diastereoselective Synthesis of Five‐ and Seven‐Membered Rings by [2+2+1], [3+2], [3+2+2], and [4+3] Carbocyclization Reactions of β‐Substituted (Alkenyl)(methoxy)carbene Complexes with Methyl Ketone Lithium Enolates

“…Keywords: carbenes · carbocycles · cyclization · enolates cyclization reaction of alkenyl chromium carbene complexes and alkynes has been described in which the carbene complexes act as a C 3 unit. Alternatively, while lithium enolates add to a,b-unsaturated carbene complexes in a Michael fashion, [21] Casey and Brunsvold [21a] described only an example in which the lithium enolate of acetone added to these complexes through 1,2-nucleophilic attack to furnish a,b-unsaturated ketones. In this context, we have recently [22] reported the novel and solvent-controlled diastereoselective [3+2] and [4+1] cyclization reactions of a,b-substituted (alkenyl)(methoxy)carbene complexes and methyl ketone lithium enolates to form five-membered carbocyclic rings.…”

Transition metal carbene chemistry7: Nucleophilic substitution reactions of imidazolide and benzimidazolide ions with Fischer carbene complexes in MeOH

“…Though, in most synthetic applications the common nucleophiles used include amines [2,[4][5][6][7][8], hydrazine [2,9], oximes [2,10], alkoxide ions [2,4,11], thiolate ions [2,4, [12][13][14], carbanions [14][15][16][17][18][19], (mainly aryl and alkyl lithium) as well as others [2, [20][21][22], the first kinetic investigation on nucleophilic substitution reaction was that of Werner et al who studied the reaction of 4-Cr-Z with several primary aliphatic amines (n-BuNH 2 , C 6 H 11 NH 2 , C 6 H 5 CH 2 NH 2 ) in n-decane, dioxane, methanol and dioxane-methanol (1:1) [8]. There have been few other kinetic studies in the early literature; these investigations focused mainly on reactions with amines [4, [23][24][25] and phosphines [4, 26,27] in weakly polar organic solvents.…”