Preparation lithium naphthalide

This approach frequently leads to the most active metals as the relatively short reduction times at low temperatures leads to reduced sintering of the metal particles and hence higher reactivity. Fujita, et aL(62) have recently shown that lithium naphthalide in tqluepe can be prepared by sonicating lithium, naphthalene, and N, N, N, N-tetramethylethylene-diamine (TMEDA) in toluene. This allows reductions of metal salts in hydrocarbon solvents. This proved to be especially beneficial with cadmium(49). An extension of this approach is to use the solid dilithium salt of the dianion of naphthalene. Use of this reducing agent in a hydrocarbon solvent is essential in the preparation of highly reactive uranium(54). This will be discussed in detail below. 

The highly reactive cadmium can be prepared by two different methods. One approach is a room temperature reduction of CdC with lithium naphthalide in THF or DME. The second approach allows the preparation of the reactive metal in a hydrocarbon solvent. First, lithium naphthalide is prepared in benzene addition of this solution to CdC produces a highly reactive cadmium powder. 

Procedure B. Finely cut (0.15 g, 22.0 mmol) and a stoichiometrical amount of naphthalene (2.80 g, 22.0 mmol) were weighed into a 100-ml flask, and ZnCl2 (1.5 g, 11.0 mmol) was weighed into a 50-ml flask. The Lithium and naphthalene were dissolved in THF (20 ml) in ca. 2h. ZnCl2 was dissolved in THF (20 ml) and the solution was transferred into the flask with lithium naphthalide via cannula over 10 min. The reaction mixture was further stirred for 1 h, and the resulting black suspension of active zinc thus prepared was ready for use. 

Cadmium(0). A reactive cadmium powder can be prepared by reaction of CdCl2 with lithium naphthalide in glyme or THF. A more reactive cadmium powder is obtained by reaction of CdCl2 with lithium naphthalide prepared by sonication in TMEDA and toluene. A third form is prepared by treatment of Cd3Li with 1 equiv. of I2 to leach the lithium. 

In the application of this methodology to the preparation of C-glycosides, Beau and Sinay [183] utilized dimethyl carbonate as an electrophile. As shown in Scheme 7.65, the resulting product mixture favored the (3 oriented ester group in a ratio of 20 1. Subsequent reductive cleavage of the phenylsulfone was accomplished on treatment with lithium naphthalide giving the a-C-glycoside in 72% overall yield. Similar results were observed when phenyl benzoate was used as an electrophile. 

The examples presented in the previous two sections represent early approaches to the preparation of C-disaccharides. Building upon these early studies, new techniques became apparent and interesting reports surfaced in 1985. Aside from additional studies involving Diels-Alder methodology, Beau, et al.,7 reported the use of addition reactions between phenylsulfone anions and sugar-derived aldehydes as a viable method for the formation of C-disaccharides. As shown in Scheme 8.3.1, the sulfone associated with the addition product was cleaved on treatment with lithium naphthalide thus giving the final product. 

Lithium naphthalide and uranocene in thf give the monoanion [U(r/-cot)2], isolated as a solvated lithium salt (405) neutral (406) and anionic (407) neptunium and plutonium analogs have also been prepared. 

Using the method of Fujita et al. [78], we were able to prepare a highly active form of cadmium in toluene [32]. This method works for uranium as well but is inconvenient as sonication is needed for each reaction. We have prepared and isolated the stable crystalline lithium naphthalide dianion derivative [(TMEDA)Li]2[Nap] 2 directly by sonicating a 1.6M solution of TMEDA, Li, and naphthalene in toluene. When sonication is stopped after all of the Li has dissolved, the dianion crystallizes. This complex was prepared previously by deprotonation of 1,4-dihydronaphthalene [79] but has not been used in any synthetic chemistry. The 1,4-dihydronaphthalene that was employed is a fairly expensive and sensitive compound, precluding its widespread use in synthesis. Our procedure is much less expensive and amenable to preparative scale synthesis. We prepared 50-60 g quantities of this complex and found it to be indefinitely stable at room temperature when stored in an argon-filled dry box. Complex 2, however, does decompose under nitrogen. 

A freshly prepared suspension of lithium naphthalide (194 mmol) in 200 mL THF is added at 70°C slowly and dropwise over 5 h to a solution of (f-Bu)2SiBr2 (29.38 g, 97.2 mmol) in 150 mL THF. The temperature is increased to ambient under stirring of about 12 h. THF is distilled off and the residue extracted with 400 mL petrol ether 40/60. After filtration the petrol ether is removed by distillation and the naphthalene is sublimed off at 55°C/ 0.01 mbar. The residue is again dissolved in petrol ether 40/60, filtered over a 10 cm layer of silica gel 60. After reducing the volume of the solution by evaporation, the product is crystallized at -25°C to yield 10.74 g (78%) of /-Bu2Si)3 as yellow crystals. 

Crystallisable salts and related compounds. Almost all crystallisable catalysts, such as sodium and lithium aromatic compounds (e.g. sodium naphthalide), -oyl salts such as aroyl hexafluorophosphates, alkoxides, and many others can be prepared in a vacuum system and then purified by repeated crystallisations and washings in a closed system (see Chapter 5) thereafter they can be distributed into breakable phials or other devices as described in Chapter 3. 

Intercalation and ion exchange reactions can provide a viable method to prepare many ternary chalcogenides that cannot be obtained otherwise. Ternary phases can be obtained by exposing layered MX2 to appropriate metal vapor [76], alkali metal in liquid ammonia solution, or organometallic reductant such as n-butyl lithium or sodium naphthalide [77-80]. One advantage of the intercalation approach is that the ternary phases can be obtained at low temperatures. Further details of this synthetic method will be described within the section on intercalation reactions. 

It should be noted that the preparation of n-type (reduced) polyacetylene using strong organic bases (e.g., alkyl lithium compounds) or more commonly electron transfer reagents (e.g., sodium naphthalide radical anion) employs the two major classes of initiators used in anionic polymerization of monomers such as styrene and butadiene. Reductive doping can also be accomplished by deprotonation of, for example, acetylene/butadiene copolymers and related phenylenepentadienylenes." ... 

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