Grignard reagents addition reactions

But apart from unexpected side reactions, various well-known competing reactions, such as reduction, conjugated addition, and enolization reactions, may well hinder the studies of mechanistic aspects of Grignard reagent reactions. In view of all such unknown factors, it may not come as a surprise that in one of the latest publications on some mechanistic aspects of Grignard reagent addition reactions, in the Journal of Organic Chemistry, the authors started their report with the remark that... 

Magnesio-ene reaction, 46 47, 356 357 Mechanism of Barbier reaction, 406 407 Mechanism of Grignard reagents addition reactions. 219 248 concerted (polar), 221, 237 242 cyclic transition state see Mechanism of Grignard reagents, addition reactions, concerted [polar]) development of reactivity spectrum. 225-235, 246... 

Gomberg reaction, 333 Grignard reagents addition to 0=C—C=0, 201 addition to C=N, 244 addition to 0=0, 221,235, 238 structure, 221 Ground state carbon, 3 dienes, 13... 

The reaction vessel should be cooled with an ice-salt bath (rather than an acetone-dry ice bath as specified in the published procedure) during the addition of the PSCI3 solution to the Grignard reagent. The reaction temperature should be monitored carefully. If it falls below -5°, the addition should be stopped and the reaction mixture cautiously rewarmed to 0-5° before addition is resumed. 

Introduction. Ti-TADDOLates are a,a,a, a -tetraaryl-2,2-disubstituted l,3-dioxolane-4,5-dimethanolatotitanium derivatives. The most common substituents are R, R = Me/Me and Ph/Me, Ar=Ph and 2-naphthyl, X, Y = C1/C1, t-PrO/Cl, Cp/Cl, and i-PrO/i-PtO. The corresponding TADDOLs (2) are available in both enantiomeric forms from tartrate esters which are acetalized (R R CO) and allowed to react with aryl Grignard reagents. The reactions performed in the presence of Ti-TADDOLates or with Ti-TADDOLate derivatives include nucleophilic additions to aldehydes - - and nitroalkenes of alkyl, aryl, and allylic - groups aldol additions hydrophosphonylations and cyanohydrin reactions of aldehydes inter- and intramolecular Diels-Alder additions ... 

With organolithium reagents, stable intermediates are produced by addition to a carboxylic acid. On workup, these intermediates produce ketones. As with Grignard reagents, the reaction of organolithium reagents with esters produces tertiary alcohols because the intermediates decompose to ketones under the reaction conditions. The mechanisms for these processes are illustrated in the examples that follow. 

Both the silyl derivative (59) and the alcohol (60) may be used as sources of the iminium salt (61) in reactions with a wide variety of nucleophiles. In practice, it was found feasible to use Grignard reagents for reaction with the silyl derivative, while TiC was effective in promoting attack on the carbinol amine by weaker nucleophiles. The process is shown in Scheme 24 using the addition of indole as an example. 

Najera et al. [40,41] reported addition reactions to a variety of aryl sulfones. The Grignard reagent addition to an a,j9-unsaturated sulfone (an enoyl sulfone) is depicted in Eq. (12). In this reaction, the major product is formed from conjugate addition to the... 

There are three main batch process protocols for reaction of silanes with Grignard reagents. Addition of the silane to the Grignard reagent (normal addition) is preferred when full substitution is desired. The reaction is single-pot , in that the Grignard can be formed and then reacted without transfer. An example of a product produced by normal addition is triethylsilane. Addition of the Grignard to the silanes (reverse addition) is preferred... 

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