Imines organozincs

Reactions of Organozinc Reagents with Imines and Other C=N... 

Other examples of ZnR2-initiated radical additions to C=N bond-containing compounds can be found in a recent review by Miyabe et al 7 Overall, radical additions to imines and related derivatives may be considered as a valuable alternative to nucleophilic additions, particularly for the introduction of secondary and tertiary alkyl groups. In general, organozinc-mediated radical reactions are a new and significant direction with great potential.382,385... 

For enantioselective copper catalyzed addition of organozinc reagents to imines, see [97-116]. Enantioselective Ni-catalyzed alkyne, imine, triethylborane 3-component coupling has been reported, but modest selectivities (51-89% ee) are observed. For this method, vinylation is accompanied by ethyl transfer [149]... 

Nowadays, this chemistry includes a wide range of applications. The organozinc compounds employed in the enantioselective addition include dialkylzincs, dialkenylzincs, dialkynylzincs, diarylzincs and the related unsymmetrical diorganozincs. Electrophiles have been expanded to aldehydes, ketones and imines. Asymmetric amplification has been observed in the enantioselective addition of organozincs. Recently, asymmetric autocatalysis, i.e. automultiplication of chiral compounds, has been created in organozinc addition to aldehydes. 

Keywords Catalyst, Alkylation, Allylation, Arylation, Mannich reaction, Carbon-nitrogen double bond, Imine, Nitrone, Aldimine, Organozinc reagents, Silyl ketene acetal, Silyl enol ether, Amine, (3-Amino acid... 

Catalytic Enantioselective Alkylation of Imines with Organozinc Reagents... 

Quite recently, there has been significant expansion and development in the alkylation of imines with organozinc reagents using chiral Lewis acid catalysts. In 2000, Tomioka and co-workers reported a copper(II)-chiral amidophos-phine 4-catalyzed asymmetric process for the addition of diethylzinc to N-sul-fonylimines (Scheme 2) [8]. Excellent enantioselectivities (90-94%) and yields (83-99%) were obtained in reactions of N-sulfonylimines derived from arylal-dehydes. 

The Reformatsky-type addition of organozinc reagents to imines is a well-known process for / -aminoester synthesis. However, this transformation often affords... 

Fig. 34 Nickel-catalyzed 1,3-rearrangement of ter/ hutylsullinyl imines with organozinc bromides...

Enantiomerically enriched or pure benzaldehydeimine complexes react with nucleophiles such as Grignard see Grignard Reagents) and organozinc reagents, and they participate in a number of cycloaddition reactions. Enantiopure tricyclic /3-lactams can be obtained from stereoselective [2 - - 2]cycloaddition between a complexed chiral benzaldehyde imine and a ketene (Scheme 85). For example, reaction of (44) with acetoxyketene gives (45). 

The development of organozinc addition reactions to imines and imine derivatives has been somewhat limited by both the poor electrophilicity of the azomethine carbon and the low reactivity of organozinc reagents. 

Even the very efficient enantioselective catalysts used in organozinc addition reactions to carbonyl compounds failed to catalyze the corresponding addition reactions to nonactivated imines such as A-silyl-, A-phenyl-, or iV-benzyl-imines. However, enantioselective additions of diaUcylzinc compounds to more activated imines, like iV-acyl- or iV-phosphinoyl-imines, in the presence of catalytic or stoichiometric amounts of chiral (see Chiral) aminoalcohols, have been recently reported. For example, in presence of 1 equiv of (A,A-dibutylnorephedrine) (DBNE) diethylzinc reacts with masked A-acyl imines like A-(amidobenzyl)benzotriazoles, to give chiral A-(l-phenylpropyl)amides with up to 76% e.e. (equation 68). 

Ligand evaluation continues for enantioselective addition of organozinc reagents to aldehydes, including the substituted BINOL 34, the ferrocene derivative 35, an imine 36 from 2-amino-1,2,2-triphenylethanol, as well as the Cj-symmetric 37 and enf-38. ... 

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