Imines reactions with Fischer carbene complexes

Imines have been employed in [3+2] cycloaddition reactions with Fischer carbene complexes leading to 3-pyrroline derivatives, as shown by the conversion of the reactants 441 and 442 to the product 443 (Equation 123). The preferred stereochemistry of the resulting 3-pyrrolines is trans, with minor amounts of the m-isomers <2000JA11741 >. 

One of the earliest reported thermal reactions of Fischer carbene complexes was the reaction with olefins to give cyclopropanes [127]. More recently it has been shown that photolysis accelerates inter molecular cydopropanation of electron-poor alkenes [128]. Photolysis of Group 6 imine carbenes with alkenes... 

Reaction of a,/MJnsaturated Fischer Carbene Complexes with Alkenes, Butadienes, Enamines, and Imines... 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Akiyama developed a novel [3+2] cycloaddition reaction of alkenyl Fischer carbene complexes 11 with simple imines 12 in the presence of a catalytic amount of GaCb to produce 3-alkoxy-2,5-disubstituted-3-pyrroline derivatives 13 <00JA11741>. 

Alkenylpyrroles 23, which readily underwent hydrolysis to 24, have been prepared via reaction of enyne-imines 25 or the corresponding enyne-A.A -dimethylhydrazones with the Fischer carbene complex 26. The hydrazones were found to be the more useful synthons, generally giving higher yields <030L2043>. 

Extensive studies on diastereoselectivity in the reactions of 1,3-dipoles such as nitrile oxides and nitrones have been carried out over the last 10 years. In contrast, very little work was done on the reactions of nitrile imines with chiral alkenes until the end of the 1990s and very few enantiomerically pure nitrile imines were generated. The greatest degree of selectivity so far has been achieved in cycloadditions to the Fischer chromium carbene complexes (201) to give, initially, the pyrazohne complexes 202 and 203 (111,112). These products proved to be rather unstable and were oxidized in situ with pyridine N-oxide to give predominantly the (4R,5S) product 204 in moderate yield (35-73%). 

In some cases, vinylidene complexes undergo [2-t-2] reactions that are characteristic of Fischer and Schrock carbene complexes. However, these [2+2] reactions involving vinylidene complexes can result from nucleophilic addition at the central carbon, rather than a concerted [2+2] process. For example, the reaction of an imine with the iron-vinylidene complex in Equation 13.28 leads to formation the product of a [2+2] reaction between the carbon-nitrogen double bond and the carbon-carbon double bond. ° - This reaction is believed to occur by nucleophilic attack of the nitrogen at the central carbon, followed by ring closure at the p-carbon, instead of a concerted [2+2] process. 

Encouraged by our results on stoichiometric and catalytic metathesis reactions of carbodiimides and imines with Fischer type carbene tungsten(O) complexes (9) we started 1984 with metathesis like reactions of the Schrock type carbyne tungsten (VI) complex Cl3(dme)WCtBu with heteroallenes (isocyanates, carbodiimides, isothiocyanates) and with heteroalkenes (imines and nitroso compounds). 

The reaction of Fischer alkenyl carbene complexes 101 with imines 102 in the presence of a Lewis acid generates pyrroline derivatives 105 as a result of a formal [3+2] cycloaddition via metallacyclic intermediates 103 (Scheme 5.21) [32]. The intermediates 103 are supposed to be formed through a metalla-Diels-Alder reaction. High asymmetric induction is observed in the reaction of chiral alkenyl carbene complexes 101 derived from (—)-8-phenyl-menthol. The major isomer of the trans products 104 can be... 

---