Alkylmagnesium halide

There ate numerous alkyltitaniums, and many of their reactions resemble those of alkyllithiums and alkylmagnesium halides. They ate protolyzed by water and alcohols, R Ti(R )3 + HA — RH + A-Ti(R )3 they insert oxygen, R TiR + O2 — ROTiR and they add to a carbonyl group ... 

The action of alkyllithiums and alkylmagnesium halides with functional groups on pyrimidines has been mentioned in appropriate sections on the reactivity of the substrates. 

Reactions of Enamine Salts with OrganometalUc Compounds Organolithium and organomagnesium compounds react with enamine salts to give amines substituted on the ix-carbon atoms. The treatment of. -dehydroquinolizidinium perchlorate (163) with alkylmagnesium halides gives 9-alkylated quinolizidines (164) (252,256). Formation of... 

Many other kinds of organometallic compounds can be prepared in a manner similar to that of Grignard reagents. For instance, alkyllithium reagents, RLi, can be prepared by the reaction of an alkyl halide with lithium metal. Alkyllithiums are both nucleophiles and strong bases, and their chemistry is similar in many respects to that of alkylmagnesium halides. 

Grignard reagents, there is an equilibrium between an alkylmagnesium halide and a dialkylmagnesium. 

The aforementioned observations have significant mechanistic implications. As illustrated in Eqs. 6.2—6.4, in the chemistry of zirconocene—alkene complexes derived from longer chain alkylmagnesium halides, several additional selectivity issues present themselves. (1) The derived transition metal—alkene complex can exist in two diastereomeric forms, exemplified in Eqs. 6.2 and 6.3 by (R)-8 anti and syn reaction through these stereoisomeric complexes can lead to the formation of different product diastereomers (compare Eqs. 6.2 and 6.3, or Eqs. 6.3 and 6.4). The data in Table 6.2 indicate that the mode of addition shown in Eq. 6.2 is preferred. (2) As illustrated in Eqs. 6.3 and 6.4, the carbomagnesation process can afford either the n-alkyl or the branched product. Alkene substrate insertion from the more substituted front of the zirconocene—alkene system affords the branched isomer (Eq. 6.3), whereas reaction from the less substituted end of the (ebthi)Zr—alkene system leads to the formation of the straight-chain product (Eq. 6.4). The results shown in Table 6.2 indicate that, depending on the reaction conditions, products derived from the two isomeric metallacyclopentane formations can be formed competitively. 

Improved yields of cyclopropylamines 47 could be obtained by using methyltitanium triisopropoxide (53) instead of titanium tetraisopropoxide [108], as well as by adding the Grignard reagent to the mixture of the amide and the titanium reagent at ambient rather than low temperature (Schemes 11.15 and 11.16, and Table 11.9) [67,69]. In principle, methyltitanium triisopropoxide requires only one equivalent of the alkylmagnesium halide to generate a dialkyltitanium diisopropoxide intermediate 55, and in this particular case P-hydride elimination can only occur at the non-methyl substituent so that methane... 

In the hydroxycyclopropanation of alkenes, esters may be more reactive than N,N-dialkylcarboxamides, as is illustrated by the exclusive formation of the disubstituted cyclopropanol 75 from the succinic acid monoester monoamide 73 (Scheme 11.21) [91]. However, the reactivities of both ester- as well as amide-carbonyl groups can be significantly influenced by the steric bulk around them [81,91]. Thus, in intermolecular competitions for reaction with the titanacydopropane intermediate derived from an alkylmagnesium halide and titanium tetraisopropoxide or methyltitanium triisoprop-oxide, between N,N-dibenzylformamide (48) and tert-butyl acetate (76) as well as between N,N-dibenzylacetamide (78) and tert-butyl acetate (76), the amide won in both cases and only the corresponding cyclopropylamines 77 and 79, respectively, were obtained (Scheme 11.21) [62,119]. 

The Grignard route to diorganyl ditellurides suffers from lack of generality and the mechanism of the oxidation seems to be uncertain. Alkylmagnesium halides demonstrate lack of reactivity towards elemental tellurium/ whereas aryhnagnesium halides in ether as the solvent furnish a mixture of ditellurides and tellurides. Satisfactory results are obtained by tellurium insertion in aryhnagnesium halides in THF followed by oxidation before or after aqueous work-up. ... 

In contrast to the metallation with alkyllithium or alkali amides, Grignardation of HOCR with alkylmagnesium halide is not an instantaneous reaction. The more acidic 1,3-diynes and hetero-subsdtuled acetylenes react most readily. In the other cases heating for several minutes... 

A similar set of reactions has been carried out with cyclic allyl ethers and alkylmagnesium halides using the same nickel catalyst, however, the optical yields are generally low (< 60 %)21 with the exception of the following example213. The optical purity and configuration of the product was established by chemical correlation with 3-ethvlhexanedioic acid. 

Titanocene dichloride also catalyzes a regioselective carbomagnesiation of alkenes 187 (equation 115) and dienes 188 (equation 116). The reaction proceeds at 0°C in THF in the presence of Cp2TiCl2, an organic halide and n-BuMgCl which leads to the catalytic species, affording benzyl, allyl or a-silyl alkylmagnesium halides, which are trapped with electrophiles (equation 117) . ... 

In the absence of additives the yield of the alcohol 212 is only 17%, and 53% in the presence of CeCls. Catalytic amounts of zinc chloride in the presence of LiCl were found to have a similar positive effect on the outcome of the 1,2-addition reaction of alkylmagnesium halides to enolizable ketones (equations 138 and 139). Due to the low price of ZnCli, this method seems promising for large-scale applications. 

In 1982, JnUa s group showed that vinyl snUones react with Grignard reagents in the presence of iron salts to afford moderate yields of conpling product (Scheme 25). The reaction is stereoselective but its scope is limited. Thus, with secondary alkylmagnesium halides, only the reduction product is formed. 

Similarly, pentafluorophenylmagnesium halides can be prepared either by direct reaction of magnesium with pentafluorophenyl halides or by an exchange reaction of alkylmagnesium halides with hydro-, bromo- and chloropentafluoro-benzenes [195,213-217] (Scheme 73). 

Reactions of aryl- and alkylmagnesium halides with sulfur tetrafluoride do not result in fluori-nation of the organic part of the organometallic compound diaryl- or dialkyl sulfides and aryl or alkyl halides are the sole products.233... 

Anion radical Alkyl Halide Alkylmagnesium halide... 

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