Organometallic reagents allylic

L3.3.3.3.1.1.1. From Allylic Organometallic Reagents and Electrophilic Boranes (a) Allylboranes and Allylboronates... 

Silicon-based Lewis acids have been known for some time, and the related chemistry in catalysis has recently been reviewed [24]. Most examples in the literature are mainly based on achiral species and will be discussed only briefly in this section. In general, a broad variety of reactions can be catalyzed with compounds like MejSiOTf, MejSiNTf or MOjSiClO. One advantage over some metal Lewis acids is that they are compatible with many carbon nucleophiles like silyl enol ethers, allyl organometallic reagents and cuprates. 

Denmark, S. E. Fu, J. Catalytic enantioselec-tive addition of allylic organometallic reagents to aldehydes and ketones. Chem. Rev. 2003,... 

The formation of chiral secondary homoallylic alcohols via the enantioselective addition of allylic nucleophiles to aldehydes is an important tool in organic synthesis. An efficient way to achieve this transformation is to use allylic organometallic reagents in the presence of chiral Lewis acid catalysts. The most widely studied catalysts in the area... 

In the studies of SnCl4 or BF3 0Et2-promoted intramolecular addition of allylic organometallic reagents to aldehydes to clarify the origin of the stereoselectivity. 

The purpose of this review is to provide a summary (through to the end of 1988) of the uncatalyzed reactions of type I and type III allyl organometallics with C X electrophiles. Most of the examples involve aldehydes and ketones, but the reactions of allyl organometallics with imines are also covered. Because the focus of this review is on selectivity and synthetic efficiency, this review is not intended to be as comprehensive as an Organic Reactions chapter or a Chemical Reviews article. Rather, we have attempted to define and illustrate the factors that influence stereoselectivity, to provide access to the most pertinent literature, and, most importantly, to provide a basis for selection of an allyl organometallic reagent for application in specific synthetic problems. 

A number of highly enantioselective chiral allyl organometallic reagents have been described in the literature. These are of considerable interest both for the asymmetric synthesis of homoallyl alcohols as well as in double asymmetric reactions with chiral C=X electrophiles. - Two distinct groups of chiral allyl metal reagents can be identified those with conventional, easily introduced chiral auxiliaries and ones in which the center of chirality is a structural component of the reagent (e.g. allyl metal compounds with substituents at C-1). These are discussed separately in the sections that follow. 

Using Allyl Organometallic Reagents 4.3.2. .1 Achiral imines... 

Gilman and Eisch were the first to recognize that allyl organometallic reagents possess superior reactivity relative to ordinary, nonresonance-stabilized organometallic reagents in imine addition re-... 

Figure 1 Resonance stabilization of the allyl anion in allyl organometallic reagents results in greater ionization of...

Table 1 Survey of Allyl Organometallic Reagents Known to React with Imines, Iminium Salts and Related...

Table 2 Yields of Homoallylamines Formed in the Reactions of Allyl Organometallic Reagents with Achiral...

Table 9 1,3-Asymmetric Induction in the Addition of Allyl Organometallic Reagents (37) to Glyoxylate Aldimines (36) Derived from Chiral Amines (Equation 9) - ...

Yamamoto et al. ° have examined the addition of allyl organometallic reagents to a-alkoxyaldimines (40) derived from (S)-2-methoxy(methoxy)propionaldehyde and (/ )- and (S)-l-phenylethylamine (equation 10). The results are summarized in Table 10. Chelation control with allyl-AlEtaMgCl, -MgCTl and -ZnBr (entries 1-3, Table 10) and nonchelation (Cram) control with allyl-Ti(Pi O)3, -B(OMe)2 and -9-BBN (entries 4-6, Table 10) parallels that observed in the allyl metal-a-alkoxyaldimine additions (involving aldimines that lack a chiral nitrogen substituent) shown in Table 6. The chirality of the a-alkoxy... 

Table 25 Reactions of Allyl Organometallic Reagents with gem-Amino Ethers (133 Scheme 11)...

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