Grignard reagents, addition

A high level of activity continues in connection with the synthesis of antimalarial artemisinin analogues and congeners, in which the 1,2-dioxepane moiety is embedded. Recent examples include the syntheses of various 10-substituted deoxoartemisinins of type 123 (eg. R1 = Cl COMe) from dihydroartemisinin acetate, and of type 124 (eg. R2 = a-OH, R3 = Me), from Grignard reagent addition to 10-(2-oxoethyl)deoxoartemisinin . 

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... 

SCHEME 2. A termolecular mechanism for Grignard reagent addition to carbonyl compounds via... 

Isoxazolines 54, prepared by stereoselective 1,3-DC of nitrile oxides and enantiopure allylic alcohols, were converted into p-amino acids 56 eind 58 by nucleophilic addition to the C=N bond followed by reductive cleavage of the N-0 bond and oxidative cleavage of the diol moiety. The facial selectivity in the nucleophilic addition was dictated by the C-5 substituent in either a directed (hydride addition) or a sterically (Grignard reagents addition) controlled manner <03JA6846>. 

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... 

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... 

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... 

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