Addition of Other Organometallics. Including Grignards

2-Additions of a range of organolithium reagents, RLi, ArLi, NC-CH2Li, RC=CLi, and ArC=CLi, show ees of 65-98%, using a chiral lithium aminosulfide auxiliary, superior to similar lithium amides with an ether instead of a sulfide, or without either 

Lithium carbazolates have been added enantioselectively to aldehydes, giving heterocyclic carbinols.233 

The preparation and synthetic applications of a-lithio aldehydes and ketones and related compounds have been reviewed.234 

Mixed lanthanide-alkali chlorides, LnCl3.2LiCl (Ln = La, Ce, Nd) can be readily prepared as 0.5 mol dm-3 solutions in THF.235 They act as improved promoters of addition of organomagnesium reagents to ketones, and also to aldimines, and in addition have been found to promote organolithium addition. 

6-Trimethoxybenzene-l,3,5-tricarbaldehyde (79) and its keto homologue (80) involve three symmetry-equivalent carbonyl centres, each in a 1,5-relationship to their neighbours.236 Two diastereoselective reactions have been performed (i) the trial can be trimethylated to give triol (81) with methyllithium in THF, and (ii) the triketone can be reduced (to the same product), in both cases with 95% de (anti, syn). Chelation and steric (gearing) effects about the crowded aromatic core are discussed to explain the observed diastereoselectivity. 

Diastereoselective and enantioselective addition of alkylmetal reagents to aldehydes, ketones, and imines has been reviewed. (g) 

Organolithiums have been added to Q ,j8-unsaturated ketones, aldehydes, and imines in the presence of lithium bromide.  

BINOL-derived methylols (126) catalyse the previously challenging enantioselective addition of methylmagnesium bromide and other Grignards to aldehydes. (g) 

Organometallics - Grignards and organozincs - have been added to A-protected aziridine-2-carboxaldehydes (127) with 99% jyn-diastereoselectivity in some cases.  

Sugar-monophosphites have been employed as chiral ligands in the nickel-catalysed enantioselective alkylation of aryl aldehydes by a range of alkylaluminium reagents.  

Aggregation between lithiated dipolar entities throughout a catalytic cycle for enantioselective hydroxyalkylation of an aldehyde by cat -RLi has been studied. Up to 90% 

DFT computations for BuLi addition to PhCHO in the presence of chiral A,P-amides R NHC H(R)CH2PPh2 derived from amino acids have reproduced the enantioselectiv- 

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Distinction between PL and ET mechanisms is not straightforward. Various experimental methods have been used so far to demonstrate the ET process, including spectroscopic detection of radical intermediates detection of products indicative of radical intermediates " and measurement of secondary deuterium " and carbonyl carbon kinetic isotope effects (KlEs) "" . The combination of several experimental methods, including KIE, substituent effect and probe experiments, was shown to be useful in distinguishing the ET process from the PL process for the addition reactions of the Grignard and other organometallic reagents . 

There are many examples of the stereoselective addition of nucleophiles to carbonyl groups in which chelation to the titanium center should be critical—reported examples include the stereoselective hydride reduction of a- or /3-hydroxyketones (Eq. 305) [684-686], of a-phosphino ketones [687], of a-sulfonylketones [688], and of an a,/3-unsaturated carbonyl compound in a 1,4-fashion [689]. The stereoselective addition of organometallic compounds such as Grignard [669,690], zinc [691,692], copper [693], and other reagents [11] to carbonyl and related compoimds Ijy taking advantage of titanium chelation is a well established method in the stereoselective... 

Anionic initiation has been accomplished in a variety of solvents, both polar and nonpolar. Typically, initiation can proceed by electron transfer reactions from alkali or alkaline earth metals, polycyclic aromatic radical anions, or alkali and magnesium ketyls. The other possibility includes the nucleophilic addition of organometallic compounds to the monomers. Related monofunctional initiators comprise alkyl derivatives of alkali metals or organomagnesium compounds such as Grignard reagents. Difunctional species are alkali derivatives of a-methylstyrene tetramer or the dimer of 1,1-diphenylethylene. An overview of the initiation process in carbanionic polymerization is given in Ref. [159]. 

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