Ketone lithium/magnesium

We see from these examples that many of the carbon nucleophiles we encountered in Chapter 10 are also nucleophiles toward aldehydes and ketones (cf. Reactions 10-104-10-108 and 10-110). As we saw in Chapter 10, the initial products in many of these cases can be converted by relatively simple procedures (hydrolysis, reduction, decarboxylation, etc.) to various other products. In the reaction with terminal acetylenes, sodium acetylides are the most common reagents (when they are used, the reaction is often called the Nef reaction), but lithium, magnesium, and other metallic acetylides have also been used. A particularly convenient reagent is lithium acetylide-ethylenediamine complex, a stable, free-flowing powder that is commercially available. Alternatively, the substrate may be treated with the alkyne itself in the presence of a base, so that the acetylide is generated in situ. This procedure is called the Favorskii reaction, not to be confused with the Favorskii rearrangement (18-7). ... 

Acetals prepared from chiral diols and carbonyl compounds serve as a chiral synthetic equivalent of aldehydes or ketones. 1,3-Dioxanes synthesized from chiral 2,4-pentanediols are especially useful, and high asymmetric inductions are observed in the Lewis acid promoted reactions of a variety of organometallic compounds. After the removal of the chiral auxiliary by the oxidation and -elimination procedures, optically active alcohols are obtained. Optically active propargylic alcohols and cyanohydrins are synthesized from organosilane compounds, TMS-C CR or TMS-CN in the presence of TiCU (Scheme 24). 1 6-138 Reactive wganometals such as alkyl-lithiums, -magnesiums or -coppers also react with chiral... 

Lithium, magnesium, cerium, and cobalt derivatives of diethyl difluoromethylphosphonate readily react with a large variety of carbonyl compounds to give 2-hydroxy-1,1-difluoroalkyIphosphonates in good yields (46-99%, Scheme 3.79) after acidic workup. Aliphatic, 77,40i,528-53i matic,2 5 ° 5 2-5 " heteroaromatic, 277.61" oc,P-unsaturated227,535 aldehydes as well as cyclic, oc,P-unsaturated,525,536 gnd ethoxycarbonyl-substitutcd" " ketones have been used successfully. The presence of lithium salts in the solution increases the stability of the difluorinated carbanion.277... 

BERYLLIUM DIFLUORIDE or BERYLLIUM FLUORIDE (7787-49-7) BeFj Mixture with water form an acid solution. Incompatible with acids, caustics, chlorinated hydrocarbons, oxidizers, molten lithium, magnesium Aqueous solution is incompatible with organic anhydrides, acrylates, aleohols, aldehydes, alkylene oxides, substituted allyls, cresols, eaprolactam solution, epiehlorohydrin, ethylene dichloride, glycols, isocyanates, ketones, maleie anhydride, nitrates,... 

Polar solvents increase formations of ether groups. Nonpolar solvents, used with lithium, magnesium, or aluminum counterions, yield products that are high in ketones. " The same solvents, used with sodium or potassium counterions, form polymers with predominately polyester units. ... 

Dimethylpropanoyl)-l, 2,3,4-tetrahydroisoquinolincs 16 form dipole-stabilized lithium carbanions on deprotonation, but their addition to aldehydes or methyl ketones proceeds nevertheless with low simple diastereoselectivity22 23. However, a high preference for the formation of the w-diastereomer is observed after transmetalation with magnesium bromide22"24. 

With (Z)-amide enolates and (Z)-thioamide enolates a strong preference for sm-adducts is also observed. In general, boron or zirconium (Z)-enolates of ketones and amides display a higher simple diastereoselectivity in favor of syn-products than the corresponding lithium or magnesium enolates6,7. 

Precursors for this task were obtained by addition of /-butylmagnesium bromide to the central bond of [1.1.1 ]propellane 40a followed by conversion of the 3-f-butylbicyclo[ 1.1.1 Jpentyl-1 -y 1-magnesium bromide (88) into the ketones 89 by standard methods.27 Reaction of ketones 89 with tosyl hydrazide afforded the hydrazones 90, which gave the corresponding lithium salts 91 by reaction with MeLi in ether. These salts were dried under high vacuum and then pyrolized at 4 x 10 5 torr in the temperature range of 100-130°C and the volatile products condensed in a liquid nitrogen-cooled trap. 

The addition of carbonyl compounds towards lithiated 1-siloxy-substituted allenes does not proceed in the manner described above for alkoxyallenes. Tius and co-work-ers found that treatment of 1-siloxy-substituted allene 67 with tert-butyllithium and subsequent addition of aldehydes or ketones led to the formation of ,/i-unsaturated acyl silanes 70 (Scheme 8.19) [66]. This simple and convenient method starts with the usual lithiation of allene 67 at C-l but is followed by a migration of the silyl group from oxygen to C-l, thus forming the lithium enolate 69, which finally adds to the carbonyl species. Transmetalation of the lithiated intermediate 69 to the corresponding zinc enolate provided better access to acylsilanes derived from enolizable aldehydes. For reactions of 69 with ketones, transmetalation to a magnesium species seems to afford optimal results. 

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