By Grignard reagents

The addition of aliphatic and aromatic Grignard reagents 492a to ( /Z)-4-aryl- 

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The stereochemical course of reduction of imonium salts by Grignard reagents was found to depend on the structure of the reagent 714). Hydro-boration of enamines and oxidation with hydrogen peroxide led to amino-alcohols (7/5). While aluminum hydrogen dichloride reacted with enamines to yield mostly saturated amines and some olefins on hydrolysis, aluminum hydride gave predominantly the unsaturated products 716). 

Of greater potential practical significance, however, are the note193 and full papers194,195 in which Fabre, Julia and Verpeaux describe a new stereoselective synthesis of trisubstituted alkenes in which vinyl sulphones are attacked by Grignard reagents in the presence of iron or nickel catalysts (equations 82-84). 

Cleavage of propargyl ethers by Grignard reagents 12-2 Rearrangement of alkynes... 

TABLE 29. Displacement of chloroalkyl groups in sulphoxides by Grignard reagents ... 

Pyridinethiolate esters, which are easily prepared from acyl chlorides, also react with Grignard reagents to give ketones (see Entry 6 in Scheme 7.3).92 /V-Mclhoxy-/V-mclhylamides are also converted to ketones by Grignard reagents (see Entries 17 and 18). 

Treatment of hydroxylamines 4 (R1 = cyclohexyl, Ph or 3,4-(MeO)2CgH3) with acetone gives nitrones 5, which are transformed by Grignard reagents R2MgBr (R2 = Me, Et, Bu, Ph or allyl) into the hydroxylamines 6 the latter are converted into the hindered secondary amines 7 by means of carbon disulphide10. 

Esters cleavage with methoxide Alcohols cleavage by Grignard reagents [70, 71]... 

The heterocyclic derivative successfully protects the acid from attack by Grignard reagents or hydride-transfer reagents. The carboxylic acid group can be regenerated by acidic... 

THF is used as solvent for this reaction (Scheme 156). Indeed, THF is the solvent of choice for the alkylation of N- oxides by Grignard reagents. The following references (B-71MI20500, 74HC(14-S2)i) should be consulted for a more comprehensive coverage of these reactions. Reactions of the above type with organolithium compounds are less successful as metallation becomes a major pathway (vide infra). 

The preparation of magnesium enolates by metallation competes with nucleophilic addition. Thus, until recently, this strategy was only valuable for sterically hindered or relatively acidic substrates, which were metallated by Grignard reagents or magnesium diaUtoxydes. 

The bis-deprotonation of arylacetic acids by Grignard reagents is known and the resulting bis(bromomagnesinm) salts (equation 49) have been nsed for preparing / -hydroxy acids (Ivanov reaction). 

A few years ago, Blagonev and Ivanov described the bis-deprotonation of aryl acetic acids by Grignard reagents. These magnesinm dianions, known as Ivanov reagents, react with aldehydes and ketones. Reaction between dianions of phenylacetic acid and benzaldehyde yields the anti S-hydroxy acid as the major diastereomer anti/syn 69/22) (equation 113). This result is in agreement with the formation of a cyclic chair-like transition state according to the model of Zimmerman-Traxler . 

However, arylmagnesium organometaUics can only be used in a few cases " like an iron-catalyzed homocoupling (equation 92) . Iron catalysis is further used for the dechlorination of electron-rich aryl chlorides by Grignard reagents . ... 

Yamamoto and coworkers studied the substitution of ally lie phosphates by Grignard reagents in the presence of copper or iron salts. Only the Sn2 product is formed under copper catalysis whereas, in the presence of iron(III) acetylacetonate, the Sn2 product is generally obtained with an excellent selectivity (Scheme 49). It should be noted that aryl-, alkenyl-, aUcynyl- and aUcyhnagnesium halides can be used successfully. 

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