Organozincs silylation

In addition to organozinc, -silyl, -magnesium, and -borane reagents employed respectively in Negishi, Hiyama, Kumada, and Suzuki cross-coupling reactions with various electrophiles, organozirconium reagents were... 

All alkyl halides used in the couplings were primary, although some of them were branched or had an ester functionality. Some of the dialkylzincs had a functional group without affecting the outcome of the reaction. For example, organozinc derivative 302 with a silyl enol ether group reacted with alkyl iodide 303, affording the desired product 304 in 65% yield (Scheme 153). 

Homologation reaction of lithium enolates with bis(iodomethyl)zinc (58) yields a homoenolate, namely the organozinc derivatives bearing a carbonyl group at the /3 position (Scheme 6)55. Treatment of the lithium enolate of cyclohexanone, generated from the silyl... 

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... 

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). 

Organozinc addition reactions to unsaturated systems lead to an intermediate zinc compound which is in most cases further hydrolyzed to give the corresponding protonated organic compound. This intermediate can also be trapped by reaction with electrophiles (see Electrophile) (E+) such as aldehydes, acyl chlorides, organic halides, silyl halides, and so on. Depending on the nature of the electrophile (see... 

This configurationaly stable organozinc halide is in sharp contrast with the alkenyllithium compounds bearing silyl substituents described in Ref. [15]. 

Recently, even organozinc carbenoids have been used for the preparation of vinylcyclo-propanes. These species are formed upon reaction of zinc with an aldehyde or ketone in the presence of 1,2-bis(dichlorodimethylsilyl)ethane. A synthetic procedure that avoids competitive carbonyl coupling has been developed the carbonyl compound is added to a refluxing mixture of the reagents, namely amalgamated zinc, the silyl chloride and two equivalents of the alkene. 

A more convenient method for the preparation of functionalized organozinc species is hydroboration of an alkene followed by transmetalation with Et2Zn [36]. In this scheme, a wider range of functional organozincs is readily synthesized. For example, Knochel et al. reported that a dialkylzinc, prepared from a dienic silyl enol ether, enantiomerically added to various aldehydes in the presence of the chiral disulfonamide-titanium system (Scheme 12) [37]. 

The tremendous success in the catalytic asymmetric addition of organozinc reagents to aldehydes spurred Itsuno and co-workers to examine the reactivity of diethylzinc with silyl imines in the presence of chiral amino alcohols and diols. Unfortunately, this type of azomethine function failed to react [23a]. The use of activated N-acyl- and iV-phosphinoylimines turned out to be crucial as evidenced by the following reports on the alkylation of these functions using di-... 

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