Lithium compounds combination

Another example of a [2s+2sh-1c+1co] cycloaddition reaction was observed by Barluenga et al. in the sequential coupling reaction of a Fischer carbene complex, a ketone enolate and allylmagnesium bromide [120]. This reaction produces cyclopentanol derivatives in a [2S+2SH-1C] cycloaddition process when -substituted lithium enolates are used (see Sect. 3.1). However, the analogous reaction with /J-unsubstituted lithium enolates leads to the diastereoselective synthesis of 1,3,3,5-tetrasubstituted cyclohexane- 1,4-diols. The ring skeleton of these compounds combines the carbene ligand, the enolate framework, two carbons of the allyl unit and a carbonyl ligand. Overall, the process can be considered as a for-... 

There are numerous compounds of lithium. Its atoms combine with many other elements to form a variety of compound molecules. Some form as single oxidation states, with one lithium cation combining with one anion (+1 combines with —1), and the more complex compounds involve two positive lithium cations combining with two negative anions (+2 combines with -2). Some examples follow ... 

An efficient kinetic resolution was also observed during the (—)-sparteine-mediated deprotonation of the piperidin-2-yhnethyl carbamate rac-112 (equation 25). By treatment of rac-112 with s-BuLi/(—)-sparteine (11), the pro-S proton in (/ )-112 is removed preferentially to form the lithium compound 113, which undergoes intramolecular cyclo-carbolithiation, and the indolizidinyl-benzyllithium intermediate 114 was trapped with several electrophiles. The mismatched combination in the deprotonation of (5 )-112, leading to cp/-113, does not significantly contribute to product formation. Under optimized conditions [0.75 equivalents of s-BuLi, 0.8 equivalents of (—)-sparteine, 22 h at —78°C in diethyl ether] the indolizidine 115 was isolated with 34% yield (based on rac-112), d.r. = 98 2, e.r. = 97 3 optically active (5 )-112 was recovered (46%, 63% ee). 

These lithium compounds arc very reactive and will combine with most electrophiles—in this example the organolithium is alkylated by a benzylic halide. Treatment with aqueous acid gives the 1,4-diketone by hydrolysis of the two enol ethers. 

Sequential reaction of azines with alkyl hthium compounds and chloroformates usually affords the expected Reissert-type products 136, together with minor amounts of doubly acylated compounds 135 (Scheme 18b). Isoquinoline is likely to react directly with the alkyl-lithium compound to generate the alkylated lithio-enamine intermediate E, and this species may account for the formation of dihydroisoquinolines 135 and 136, through interaction with the electrophihc partner. Mamane recently expanded this concept by replacing the acylating agent with different electrophiles. These combinations lead exclusively to isomers 134 (Scheme 18) [118-120]. 

Other lithium compounds that also function as polymerization catalysts when combined with chelating diamines are lithium dialkylphos-phides (20), used to polymerize 1,3-butadiene, and lithium chloride (21), used to polymerize p-vinylbenzamide. 

Apparatus 2 1 three-necked, round-bottomed flask, provided with a thermometer-inlet combination and a mechanical stirrer. The suspension of the lithium compound is poured through the third neck. 

Although /-butyllithium has been successfully applied to metallate methyl vinyl ether, one might prefer to use the cheaper and less dangerous combination of ra-BuLi and r-BuOK for the metallation of simple vinyl ethers. If an excess of ethyl vinyl ether is used, quantitative metallation can be obtained. Some derivatization reactions give much better results with the lithium compounds. The requisite transformation into the lithiovinyl ethers can be carried out by addition of a solution of anhydrous lithium bromide in THF. 

Other alkaline earth metal oxides and related Group II metal oxides were screened for activity. Tests indicated that magnesia-zinc oxide combinations were about as efficient as magnesia alone. Calcium oxide, zinc oxide, and cadmium oxide were all catalysts for the reaction but were not as effective as magnesium oxide. Efficiencies of these oxides were increased by supporting them on activated alumina. In addition, it was found that sodium and lithium compounds deposited on activated alumina were active cat-... 

The deprotonation of the secondary carbamate rac-254 by -butyllithium/(-)-sparteine (diethyl ether/hexane, -78°C) is combined with an efficient kinetic resolution [Eq. (72)] [155,168]. The lithium compound (S)-256 is configuration-ally stable under these conditions and is formed with greater than 80% ee as estimated from trapping experiments. The less reactive enantiomer (R)-254 is recovered with 41 % yield and 80% ee. 

The construction of the overall cell is realized by a simple lamination (combining heat and pressure) of the three components in the correct order. Due to the sensitivity to moisture of lithium and of lithium compounds, the entire operation is run in controlled-atmosphere dry boxes or, for larger production, in dry rooms where the humidity content is maintained within > 1 % relative humidity. 

How many grams of lithium will combine with 20.0 g of sulfur to form the compound Li2S ... 

We wished to explore the use of asymmetric synthesis for the preparation of faxocenes bearing planar chirality. The main approaches are summarized in Figure 9. We attempted the route I, taking R=CH2NMe2 and using the combination sec-Buli / sparteine as the chiral base. Unfortunately a racemic ferrocenyl lithium compound was formed, as established by some electrophilic quenchings. We recently successfully developed route II (vide infra). 

For the yttric subgroup the biggest differences are observed for the Yb-Li-Ge system. The formation of two compounds (YbgLiGen and Yb5Li4Gc4) with new structure types which do not occur within any other system of this subgroup has been foimd for the 5dterbium lithium-germanium combinations. This is probably due to the tendency of ytterbium to be divalent or mixed-valent. 

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