One-Step Alternative to the Grignard Reaction

A real breakthrough in the study of Barbier-type reactions with metals different from magnesium came with the publication of A one step Alternative to the Grignard Reaction [14]. 

Fair to excellent yields were reported from Li-Barbier reactions with a variety of organic halides and aldehydes, ketones and esters (Table 3.1). 

Results from a later publication [15] are presented in Tables 3.2 and 3.3. 

Organic bromides seem to give the best results. The lower yields with iodides are almost certainly due to increased probability of a Wurtz condensation reaction taking place between the organolithium species and the iodide. 

Both alkyl and aryl halides give high yields. 

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The Barhier-type reaction of aldehydes and ketones with allyl halides (485) in the presence of Sml2, leading to homoallyl alcohols (486), has received recent interest as a one-step alternative to the Grignard reaction. However, the reactions require the use of stoichiometric amounts of the reducing Sm(III) species. Recently, the electroreductive Barhier-type allylation of carbonyl compounds in an SmH-mediated reaction has been developed [569]. The electrolysis of (485) is carried out in a DMF-SmCl3-(Mg/Ni) system in an undivided cell to give the adduct (486) in 50 85% yields (Scheme 168) [569]. Electrosynthesis of y-butyrolactones has been achieved by the reductive coupling of ethyl 3-chloropropionate with carbonyl compounds in the presence of a catalytic amount of SmCfi [570]. 

Additions to Carbonyl and Olefin Linkages A one-step alternative to the Grignard reaction has been described, in which a mixture of the carbonyl compound and the alkyl bromide is added to a suspension of Li in THF below 0 . ... 

It was in that period that lithium was successfully introduced in what was named A One-step Alternative to the Grignard Reaction (Sect. 3.3) [14]. 

However, earlier studies [69] on the kinetics of the One-step alternative to the Grignard reaction of bromobenzene, benzaldehyde and lithium in THF had led to the conclusion that... 

Based on CIDNP evidence, it is considered that a radical pathway is probably dominant in the formation of Grignard reagents from alkyl halides and magnesium. Full descriptive details of a one-step alternative to the Grignard reaction have now been given. 

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