Grignard reagents electrophilic reactions

Fiirstner et al. reported the first effective cross-coupling reaction between aryl halides (functioning as the electrophile) and Grignard reagents derived from allg l halides. Under these reaction conditions, they observed an important effect of the halide/pseudo halide source used in the reaction (aryl-X Scheme 13.16). Notably, aryl chlorides exhibited the highest reactivity and are also cheaper and easy to prepare than the corresponding bromides and iodides. On the other hand, aryl iodides and bromides, which... 

Benzo[6]thiophene, 2-(aryloxymethyl)-3-chloromethyl-synthesis, 4, 872 Benzo[6]thiophene, 2-arylthio-synthesis, 4, 931 Benzo[6]thiophene, 2-bromo-reaction with potassamide, 4, 829-830 synthesis, 4, 934 Benzo[6]thiophene, 3-bromo-Grignard reagents, 4, 831 reactions, 4, 830 synthesis, 4, 934 Benzo[6]thiophene, 4-bromo-synthesis, 4, 878, 934 Benzo[6]thiophene, 5-bromo-electrophilic substitution, 4, 797 Benzo[6]thiophene, 6-bromo-synthesis, 4, 878, 934 Benzo[6]thiophene, 5-t-buty 1-3-methyl-synthesis, 4, 880... 

The Grignard reagents prepared from the activated magnesium appear to react normally with electrophiles. Thus reactions with proton donors, ketones, and carbon dioxide afford hydrocarbons, alcohols, and carboxylic acids, respectively. The reductive coupling of ketones to pinacols had also been accomplished with the activated magnesium. ... 

Addition of sodium hydroxide to a mixture of [Co"(DMG)2] and an alkylating agent in methanol-water yields up to 50% of the organocobalt product. This appears to be the most convenient method for the preparation of organocobalt(III) derivatives, provided that the maximum yield is not required 161,163). Methods involving the reaction of Co with electrophiles are, at least with DMG complexes, more convenient than the main alternative route via Co(III) and Grignard reagents. 

Aldehydes can be obtained by reaction of Grignard reagents with triethyl orthoformate. The addition step is preceded by elimination of one of the alkoxy groups to generate an electrophilic oxonium ion. The elimination is promoted by the magnesium ion acting as a Lewis acid.93 The acetals formed by the addition are stable to the reaction conditions, but are hydrolyzed to aldehydes by aqueous acid. 

The interpretation of the basis for this stereoselectivity can be made in terms of the steric, torsional, and stereoelectronic effects discussed in connection with reduction by hydrides. It has been found that crown ethers enhance stereoselectivity in the reaction of both Grignard reagents and alkyllithium compounds.119 This effect was attributed to decreased electrophilicity of the metal cations in the presence of the crown ether. The attenuated reactivity leads to greater selectivity. 

Phosphorylthiophenes such as thiophenephosphonic acid diesters can be synthesized by reaction of thienyllithium or Grignard reagents with phosphoryl electrophiles [40],... 

An one-pot reaction of propargyl alcohols 77 with Grignard reagents followed by treatment with electrophiles producing polysubstituted furans has been described <00TL17>. 

Similar to reactions of iodopyrimidines previously mentioned in Section 6.2.2.2 (60 —> 61), the Grignard reagent 171, efficiently prepared from halopyridazine 170, was quenched with electrophiles such as acetaldehyde, ethyl cyanoformate, DMF or phenylsulfide to give 172 in acceptable yields <00T265>. 

O - P h e n y 1 - /V - e r y t h r o s y 1 nitrone (336), as a Ci,C i-bis-electrophile, when subjected to the double addition of Grignard reagents (in a domino style), leads to acyclic hydroxylamine (338) via the formation of open-chain nitrone (337 ). The reaction proceeds at 0°C with variable diastereoselectivity ranging from medium to good, depending on the organometalic reagent used (Scheme 2.140) (564). 

---