Organozincs to aldehydes

With the aim of improving understanding of the mechanism of the ferrocene-catalyzed aryl transfer reactions from organozincs to aldehydes, DPT calculations were performed in close collaboration with Norrby [64]. As a result, the experimentally observed higher reactivity of the phenyl transfer to aldehydes compared... 

Initially, mainly 3-amino alcohols were used as chiral ligands to catalyze the addition of organozincs to aldehydes. In most of the cases investigated a (-l-)-NLE was observed. Presumably this is a consequence of the greater stability of the dimeric meso-zinc alcoholate derived from the 3-amino alcohol. In addition to... 

The formation of 3,3-disubstituted allylzinc by addition of a vinyl copper reagent on the zinc carbenoid has been reviewed in full detail. The addition of the corresponding organozinc to aldehyde and imine is also fully covered in a highly didactic manner to highlight the perfectly controlled stereochemical outcome of the cascade organometallic reaction. 

Scheme 2-143. Enantioselective addition of organozincs to aldehydes catalyzed by...

This approach has been extended to the conjugate addition of primary dialkylzincs to 2-aryl- and 2-heteroaryl-nitroolefins to obtain enantioenriched 2-arylamines. Dendritic styryl TADDOLs and polymer-bound Ti-TADDOLates have proved to be very practical chiral catalysts for the enantioselective addition of organozinc to aldehydes. Likewise, the immobilization of BfNOL by a cross-linking copolymerization of styryl derivatives has allowed several enantioselective Ti- and Al-Lewis acid-mediated additions to aldehydes. Dialkylzines obtained via an 1/Zn exchange or a B/Zn exchange have also been successfully used for the enantioselective additions to... 

Numerous chiral non-S-coordinating bis(sulfonamides) have been successfully involved in the enantioselective addition of various organozinc reagents to aldehydes since the first use of tr<2 5-l(i ),2(i )-bis(trifluoromethanesulfo-namido)cyclohexane reported in 1989 by Ohno et These authors demonstrated the usefulness of this ligand in the Ti-catalysed enantioselective addition of ZnR2 to a variety of aldehydes, allowing enantioselectivities of up to 99% ee to be obtained (Scheme 3.37). 

Even if hundreds of chiral catalysts have been developed to promote the enantioselective addition of alkylzinc reagents to aldehydes with enantioselectivities over 90% ee, the addition of organozinc reagents to aldehydes is not a solved problem. For example, only very few studies on the addition of vinyl groups or acetylides and even arylzinc reagents to aldehydes have been published, in spite of the fact that the products of these reactions, chiral allylic, propargylic and aryl alcohols, are valuable chiral building blocks. 

The above studies illustrated that sp2-hybridized organozincs underwent direct addition to aldehydes rapidly, thus preventing the desired three-component couplings. However, alkenylzirconium reagents, derived from hy-... 

Addition of Organozinc Reagents to Aldehydes, Ketones, and a-Ketoesters 383... 

Addition of Organozinc Reagents to Aldehydes, Ketones, and a-Ketoesters 2.06.16.2.1 Chiral ligands used in addition reactions of diorganozincs with aldehydes... 

One of the important new directions in the study of addition reactions of organozinc compounds to aldehydes is the use of ionic liquids. Usually, application of these compounds in reactions with common organometallic reagents has a serious problem ionic solvents are usually reactive toward them, particularly Grignard and organolithium derivatives. It has been recently reported that carbonyl compounds react with allylzinc bromide formed in situ from allyl bromide and zinc in the ionic liquid 3-butyl-l-methylimidazolium tetrafluoroborate, [bmim][BF4].285 Another important finding is that the more reactive ZnEt2 alkylates aldehydes in a number of ionic liquids at room temperature.286 The best yields (up to 96%) were obtained in A-butylpyridinium tetrafluoroborate, [bpy][BF4] (Scheme 107). 

Overall, green solvents appear to be a valuable alternative to conventional solvents in addition reactions of diverse organozinc reagents to aldehydes. 

Reactions of organozincates with aldehydes and ketones were thoroughly investigated by Richey and co-workers (Scheme 115). In contrast to dialkylzincs, which do not give addition products with ketones and even aldehydes... 

A theoretical study of the reaction mechanism for addition of organozincate complexes to aldehydes was recently performed using density functional theory.298 It has been suggested that the addition takes place through formation of a four-centered transition state and, therefore, it can be considered a typical nucleophilic reaction. 

The chiral f5-dialkylamino alcohol DAIB serves as an efficient asymmetric catalyst for the addition of organozinc reagents to aldehydes. The reaction of diethylzinc with benzaldehyde in the presence of 2 mol % of (2S)-(-)-DAIB to give (S)-1-phenyl-1-propanol in 89% ee is described in the procedure which follows. DAIB exhibits the... 

In early 1990 we began to work on catalyzed carboligations using organozinc reagents [1]. The reactions commonly involved diethylzinc 2, which was added enantioselectively to aldehydes 1 affording secondary alcohols 3. Initially, bipyridine 4 [2-6], pyridine 5 [3], and sulfoximines 6 [7] were applied as catalysts, which in some cases led to enantioselectivities greater than 95% ee [8, 9]. 

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