Lithium displacement reaction

The first displacement reaction at C-2 position in carbohydrates was achieved during the study of sulfuryl chloride reaction with sucrose (92). Treatment of 3,4,6,3, 4, 6 -hexa-0-acetylsucrose 2,l -bis(chlorosulfate) with lithium chloride in hexamethylphosphoric triamide at 80°C for 20 h led to the corresponding 2,l -maimo derivative in 73% yield. 

Only one of these methods, namely the reaction of halides with lithium aluminum deuteride, is a true displacement reaction, following the same course as the previously discussed displacement of sulfonate esters (section Vl-A). Thus, lithium aluminum deuteride treatment of 7a- and 7jS-bromo-3 -benzoyloxy-5a-cholestanes (195) and (196) gives the corresponding deuterium labeled cholestanols (197) and (198) respectively." ... 

TABLE 2. Product distribution for the displacement reaction of allyl sulfones 9 with lithium dialkyl cuprates6... 

We discovered a complementary procedure for conversion of OMen to other functional groups. The ester P-OMen bond was shown to be cleaved in a stereoselective manner reductively [85,86]. The cleavage takes place with almost complete preservation of stereochemical integrity at phosphorus. The reducing agents are usually sodium or Hthium naphthalenide, lithium biphenyUde, and Hthium 4,4 -di-fert-butylbiphenyl (LDBB). The species produced is then quenched with an alkyl hahde or methanol to afford tertiary or secondary phosphines, respectively (Scheme 5b). Overall, the displacement reaction proceeds with retention of configuration. 

Sn2 and SN2 Reactions with Halides and Sulfonates. Corey and Posner discovered that lithium dimethylcuprate can replace iodine or bromine by methyl in a wide variety of compounds, including aryl, alkenyl, and alkyl derivatives. This halogen displacement reaction is more general and gives higher yields than displacements with... 

The principle of the displacement of one metal by another, or in other words of the displacement of nobler by base or not so noble metals, as described earlier, must be applied with due caution, without neglecting other effects that may not be immediately obvious from consideration of the electrochemical series. Some of these effects are illustrated in the following. Although the position of lithium is above that of sodium in the series, lithium cannot displace sodium from common salt solutions since both of these metals occupy positions higher up than hydrogen and will displace this element from the solution. It must be borne in mind, therefore, that the series applies to aqueous solutions, and the hydrogen ion, which is present in these solutions, can also take part in the displacement reactions. 

In the case of symmetrical divinyl tellurides, the displacement of both vinyl groups is achieved by employing 2 equiv of n-butyllithium. Aryl vinyl tellurides give a mixture of products, since both Ar-Te and vinyl-Te bonds are transmetallated on reaction with n-BuLi, leading to vinyl- and aryllithiums. The butyl vinyl tellurides give only the desired vinyl-lithiums. The reactions are stereospecific with retention of the C=C bond geometry. °... 

The Other Five Candidates. All the molten salt SBs reviewed above have either a Li anode or a lithium alloy, one in which Li prevails quantitatively. As to the other 5 light metals they are seldom mentioned in the literature as candidates for anodes in these SBs, except Al. In (82) it is stated that molten salt batteries with Ca or Mg anodes yield only a small proportion of their theoretical energy because (a) Ca anodes react chemically with the electrolyte, and (b) both Ca and Mg anodes are passivated at high current drains, becoming coated with resistive films of solid salts. In a melt containing Li salts, Ca replaces Li ions by the displacement reaction Ca + 2LiCl = CaCl2 + 2Li. 

Mixed trialkylstannyl and silyl derivatives have also been used in coupling reactions, with subsequent replacement of the silyl substituent by bromine, leading to species that are capable of undergoing further coupling reactions. This process was amply demonstrated by the recent synthesis of micrococcinic acid 203, which involved four palladium-catalyzed crosscoupling reactions on stannylated substrates, two palladium-catalyzed trimethylstannane replacements of bromine, two trimethylsilyl displacements by bromine, and a total of four bromine-lithium exchange reactions, on three different thiazole derivatives and one pyridine derivative (91-TL4263). 

The use of lithium aluminum hydride gives slightly lower yields and probably involves a displacement reaction by hydride ion. The zinc-copper couple technique probably involves formation of an organozinc intermediate. Sodium, magnesium, and aluminum metal may be used to replace the zinc-copper couple [59a, b]. These organometal intermediates react with aldehydes and... 

The lithium-copper oxide cell is voltage compatible (OCV = 1.5 V), i.e. it may be used as a direct replacement for conventional Leclanche or alkaline zinc cells. CuO has a particularly high volumetric capacity (4.2 Ah/cm3) so that cells are characterized by high specific energy -300 Wh/kg (700 Wh/dm3). The discharge curve shows a single step which may be attributed to the simple displacement reaction ... 

A less common approach to the synthesis of phosphinates is the reaction of electrophilic phosphonates with carbon nucleophiles such as Grignard reagents or lithium enolates. For example, the phosphinic acid analogue 71 of the amino acid statine was synthesized by displacement of tert-butyl lithioacetate on a 5-phenyl phosphonothioate 70 (Scheme 23)d104l The racemic diastereomers of the 5-phenyl phosphonothioate were obtained in pure form, and the displacement of the phenylsulfanyl moiety was found to be stereospecific, although the stereocenter at phosphorus would later be lost on hydrolysis of the ester. A similar displacement reaction has been described using the p h osp h on och I ori d ate.1711... 

Cyclic sulfites (68) also are opened by nucleophiles, although they are less reactive than cyclic sulfates and require higher reaction temperatures for the opening reaction. Cyclic sulfite 77, in which the hydroxamic ester is too labile to withstand ruthenium tetroxide oxidation of the sulfite, is opened to 78 in 76% yield by reaction with lithium azide in hot DMF [82], Cyclic sulfite 79 is opened with nucleophiles such as azide ion [83] or bromide ion [84], by using elevated temperatures in polar aprotic solvents. Structures such as 80 generally are not isolated but as in the case of 80 are carried on (when X = N3) to amino alcohols [83] or (when X = Br) to maleates [84] by reduction. Yields are good and for compounds unaffected by the harsher conditions needed to achieve the displacement reaction, use of the cyclic sulfite eliminates the added step of oxidation to the sulfate. 

The benefits of initial product studies, followed by a more detailed examination using isotopic labelling, are well illustrated by the amination of halobenzenes, Scheme 2.7. The reaction of p-bromomethoxybenzene (15) with lithium diethylamide in ether gives a 1 1 mixture of m- and p-diethylamino-substituted products (16 and 17), with no trace of the o-isomer. One possible mechanism for these and many related reactions was that a normal direct displacement reaction to give 17 was in competition with an abnormal displacement,... 

Although lower-order cuprate reagents will often engage in displacement reactions with alkyl halides, such reactions are usually slow. They are generally much less facile than 1,4-addition reactions to a,P-unsaturated enones or enoates. The latter processes are particularly facile when trimethylsilyl chloride is employed as an additive. It was Corey and Boaz10 who first recognised the accelerating effect of trimethylsilyl chloride on cuprate addition reactions to a,p-unsaturated carbonyls. Buszek therefore capitalised on Corey s earlier observations in his reaction of 10 with lithium dimethylcuprate to obtain 15. 

K. D. Berlin, T. H. Austin, M. E. Peterson u. M. Nagabhushanam, Nucleophilic Displacement Reactions on Phosphorus Halides and Esters by Grignard and Lithium Reagents, Topics in Phosphorus Chemistry 1, 17 (1974). 

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