Asymmetric with organometallic reagent

Copper-catalyzed asymmetric allylic alkylations with organometallic reagents used for small-ring openings, such as epoxides and aziridines, have gained interest. Illustrating... 

Asymmetric synthesis of dihydropyridones. 8-Phenylmenthol has been used frequently as a chiral auxiliary, but this derivative (1) is more effective as the chiral auxiliary for enantioselective reactions of N-acylpyridinium salts with organometallic reagents. Thus 2, prepared by reaction of 4-methoxy-3-(triisopropylsilyl)pyridine with the chloroformate of 1 reacts with the Grignard reagent 3 to give an adduct that on acidic deprotection provides the dihydropyridone 4 in 94% de. Conversion of the alcohol to a chloride [P(C6H5)3 and NCS] followed by treatment with sodium methoxide in methanol cleaves the chiral auxiliary as the methyl carbonate (94% yield) and at the same time effects cyclization to form the chiral bicyclic dihydropyridone 5 in 84% yield. 

Modern aspects of electrophilic aromatic substitution chemistry address the development of enantioselective variants of these direct (hetero)arene functionalization reactions. For example, enantiomerically enriched metal catalysts, as well as organocatalysts, allowed for the asymmetric addition reactions of (hetero)arenes onto (a,P-unsaturated) carbonyl compounds. Additionally, highly enantioselective arylations of carbonyl compounds were accomplished with organometallic reagents... 

The addition of aryl groups to C=N bonds can be achieved using cooper-catalyzed asymmetric reactions with organometallic reagents. The addition of alkylzinc and related reactions is quite common in literature [47] whereas copper-catalyzed asymmetric arylation of imines is somewhat harder to find. We wish to report some successful examples of this type of catalysts. 

The asymmetric alkylation additions of the prochiral aldehydes and ketones with organometallic reagents have been studied extensively during the last several decades. Alkyltitanium complexes can be obtained from metal carbanions via titanation. Introduction of chirality at the titanium center or on the ligand (or a combination of both) enables the possibility of asymmetric induction in the carbonyl addition reaction. Since the alkyllithiums and Grignard reagents are... 

Asymmetric Allylic Substitutions on Racemic Substrates with Organometallic Reagents... 

Scheme 11 Asymmetric syntheses of 1,2-diamines with a-amino organometallic reagents...

Nitrones have a more reactive C=N bond toward nucleophilic addition compared to imines. In spite of this fact, there have been only a limited number of studies on the nucleophilic addition reactions of nitrones, particularly organometallic reagents.352-355 During the last decade, research related to reactions of nitrones with zinc-containing reagents was essentially focused on (i) dialkylzinc-assisted alkynylations356-358 and vinylations359 of nitrones, (ii) catalytic asymmetric nucleophilic additions to the C=N bond,360-364 and (iii) nitrone allylations by allylzinc halides.365,366... 

Asymmetric synthesis of amino acids.1 These lactones can serve as an optically active form of glycine for synthesis of either D- or L-amino acids. Thus (+ )-1 (or (—)-l) on radical bromination is converted into a single monobromide (2), which can be coupled with nucleophilic organometallic reagents, by either an SN1... 

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