Fisher carbenes

A combination of a Diels-Alder and a Fisher carbene-cyclopentannulation is described as the last example in this subgroup. Thus, Barluenga and coworkers used a [4+2] cycloaddition of 2-amino-l,3-butadienes 4-115 with a Fischer alkoxy-arylalky-nylcarbene complex 4-116 this is followed by a cyclopenta-annulation reaction with the aromatic ring in 4-116 to give 4-117 (Scheme 4.25) [36]. An extension of this domino process is the reaction of 4-118 with 2equiv. of the alkynyl carbene 4-119 containing an additional C-C-double bond (Table 4.2) [37]. The final product 4-120, which was obtained in high yield, is formed by a second [4+2] cycloaddition of the primarily obtained cyclopenta-annulated intermediate. 

Bicyclic cyclopropanes.1 Reaction of the Fisher carbene 1 with the 1,6-enyne 2 results in the bicyclic cyclopropane 3 (a bicyclo[3.1.0]hexane) in 69% yield. The 1,7-enyne homolog of 2 reacts with 1 in the same way to form a bicyclo[4.1.0]-... 

Ethers, sulfides, amines, carbonyl compounds, and imines are among the frequently encountered Lewis bases in the ylide formation from such metal carbene complex. The metal carbene in the ylide formation can be divided into stable Fisher carbene complex and unstable reactive metal carbene intermediates. The reaction of the former is thus stoichiometric and the latter is usually a transition metal complex-catalyzed reaction of a-diazocarbonyl compounds. The decomposition of a-diazocarbonyl compounds with catalytic transition metal complex has been the most widely used approach to generate reactive metal carbenes. For compressive reviews, see Refs 1,1a. 

Enantiopure alkynyl(alkoxy)carbene (37) complexes were produced by formal alkyne insertion into Fisher carbene complexes 39 Reaction of (37) with 1-azadiene gave functionalized 1,4-dihydropyridine (38) with high enantiomeric excess. 

The imine bond in 2-imidazolines reacts with Fisher carbenes under irradiation (Scheme 144). Low yields were obtained with monosubstituted imidazolines 608a-c due to thermal decomposition of the substrates under the reaction conditions. Optically active 4,4-disubstituted A -imidazolines 608d-e form azapenams (609d, 610e, 611) with (methoxymethylcarbene)chromium complex in good yields and high diastereoselectivity. The electronic nature of RVR clearly influences the sense of diastereoselectivity (609 vs. 610, 611) <1977JOC3586>. 

The intramolecular C-H insertion of chiral diazo compounds has been catalyzed by several metal salts derived from Ag(I), Ni(II), Pd(II), and Co(III) [64, 65]. The use of some stoichiometric chiral Fisher carbene complexes has also been reported to give the corresponding cyclic products with good selectivities [66,67]. 

The [4 + 2] cycloaddition of azadienes with alkynes is a poor reaction. However, the reactivity of dienes with Fisher carbenes has been applied to the azadiene 11 providing the 1,4-... 

Alkylation of the Fisher carbene complexes proceeds in high yields under PTC conditions (eq. 194). 

While Fischer carbene omiplexes tend not to react widi unactivated alkenes, many chromium and molybdenum Fisher carbene complexes do mtmocydoprtqianate 1,3-dienes in good yield with high levels of chemo-, regio-, and stereoselectivity... 

Norbomadienetetracarbonylchromium, in the same manner as the Fisher carbene synthesis, reacts with organolithium compounds to afford an acyl derivative by attacking the carbonyl group, and it changes to the carbene alcoholate and reacts with Et30Bp3 to produce the alkyl derivative as shown in eq. (13.44) [77J. The bond length of Cr = C is 1.942 A and it is shorter than that of Cr = C in... 

The Fisher carbenes react with imines under the irradiation of visible light to stereoselectively afford the /1-lactam, and this reaction is available for synthesis of penicillin analogues as shown in eq. (13.45). For example, benzothiazine is synthesized in a high yield by a reaction with cyclic imines as shown in eq. (13.46)... 

Fisher carbenes easily react with an amine to give the aminocarbene, and the aminocarbene reacts with carbon monoxide under light irradiation to give an aminoester as shown in eq. (13.47) [79]. If the optically active oxazolidine derivatives are used as the aminocarbene, by photolytic carbonylation the above synthesis of amino acid ester gives an optically active derivative as shown in eq. (13.48) [79]. 

Another synthetic pathway to seven-membered rings is by reacting chromium Fisher carbene complexes with... 

NHCs have been involved as additives in the self-dimerization reaction of group 6 Fisher carbenes catalysed by palladium." The use of NHCs was not shown to promote any change in the ZIE selectivities opposite to PBu 3. 

Isotopic labeling experiments. Fisher carbenes structure and reactivity. 

The reactivity of alkynyl Fisher carbene complexes (82) towards diverse oxime derivatives has been evaluated by experimental and theoretical approaches (Scheme 7). While indanone acetyloxime forms fused pyridine (83), benzophenone acetyloxime forms heterocycles (85), (86), and predominantly (84). 

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