Lithium perchlorate-nitromethan

Diels-Alder reactions of quinones generated in situ by electrochemical oxidation in lithium perchlorate-nitromethane [105]... 

The electrochemical oxidation of phenols produces quinones that can be used as dienophiles for the Diels-Alder reaction. A typical example is shown in Scheme 14, where a lithium perchlorate/nitromethane system and an electrode coated with a PTFE [poly-(tetrafluoroethylene)] fiber, to create a hydrophobic reaction layer. 

In the synthesis of a Euglobal skeleton a quinone methide has been generated in situ by anodic oxidation mediated by DDQ. The cycloaddition with unactivated alkenes was promoted by the use of lithium perchlorate/nitromethane and a hydrophobic PTFE-coated electrode (Eq. 24c) [249b]. 

Hachiya, I., Moriwaki, M., Kobayashi, S. Catalytic Friedel-Crafts acylation reactions using hafnium triflate as a catalyst in lithium perchlorate-nitromethane. Tetrahedron Lett. 1995, 36,409-412. 

Kim S, Hayashi K, Kitano Y, Tada M, Chiba K (2002) Anodic modification of proline derivatives using a lithium perchlorate/nitromethane electrolyte solution. Org Lett 4 3735-3737... 

Various electrochemical [3 -l- 2] cycloaddition reactions havebeen achieved between alkoxyphenols and olefin nucleophiles in lithium perchlorate/nitromethane electrolyte solution [18]. In these reactions, alkoxyphenols are anod-ically oxidized to generate the corresponding phenoxonium cations, which are then trapped by olefin nucleophiles to form the desired [3 + 2] cycloadducts. However, because the oxidation potentials of these [3 + 2] compounds are relatively lower than those of starting alkoxyphenols, overoxidation of the desired products can take place. To address this problem, cyclohexane is... 

FIf(OTf)4 was found to be effective in the catalytic Friedel-Crafts acylation reactions of various substituted benzenes with acid anhydrides in lithium perchlorate-nitromethane (LiC104-MeN02) (eq 24). This same system was also used for... 

Lithium perchlorate in nitromethane (LP-NM) is sometimes a more effective reaction medium than LP-DE for certain Diels-Alder reactions. The cycloaddition of 2,3-dimethylbutadiene with nitrostyrenes (Scheme 6.24) occurs with low... 

Oxidising nitromethane electrochemically by using lithium perchlorate led to a violent detonation, which was explained by the formation of an unstable metal fulminate ... 

Explosions which occurred at the auxiliary electrode during electro-oxidation reactions in nitromethane-lithium perchlorate electrolytes, may have been caused by lithium fulminate. This could have been produced by formation of the lithium salt of nitromethane and subsequent dehydration to the fulminate [1], analogous to the known formation of mercury (II) fulminate [2], This explanation is not considered tenable, however [3]. 

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

The cycloaddition of A-benzoyliminochloromethanesulfenyl chloride and 3,3-dimethyl-2-butene in nitromethane and in the presence of lithium perchlorate involves addition of the electrophile at the double bond and 1,2-methyl shift. Unusually, the ring closure is accompanied by elimination of the benzoyl group (Equation 16) <2002CHE1150>. 

The direct electrochemical oxidation of phenols generates phenoxonium cations which are able to undergo [3-1-2] cycloaddition in the presence of unactivated alkenes to produce benzofurans <1999JOC7654>. Thus, electrolysis of methyl 2,5-dihydroxybenzoate in a solution of lithium perchlorate in nitromethane in the presence of acetic acid and 2-methyl-2-butene produces the dihydrobenzofuran in excellent yield (Equation 88). 

Silver perchlorate forms deliquescent crystals, which decompose when heated to 486 Celsius. It is freely soluble in water saturated solution contains 85% by weight silver perchlorate making it one of the most water soluble compounds known lithium perchlorate being number 1. It is also soluble in aniline, pyridine, benzene, nitromethane, glycerol, and chlorobenzene. It can form solvated crystals with aniline, benzene, and toluene all explode on percussion. Silver perchlorate forms a hydrate, which melts at 43 Celsius. It can be made by reacting sodium hypochlorite (bleach) with silver bromide. 

When mcte-xylene is acylated in the presence of scandium triflate (20% mol) combined with lithium perchlorate in nitromethane, 2,4-dimethyl-acetophenone is obtained in 89% yield. In the absence of scandium triflate, lithium perchlorate is not soluble in the reaction mixture, and no acylation... 

A remarkable effect of the addition of lithium perchlorate is found in the acetylation of 2-MN 4 with AAN in the presence of anfimony(lll) triflate (5% mol). Indeed, when acetylation is performed in nifromefhane at room temperature, or in acetonitrile or methylene chloride at 50°C without lithium perchlorate, product 20 is obtained preferentially (Table 3.7). On the other hand, a dramatic change of regioselectivity is observed when the same reaction is performed in nitromethane/lithium perchlorafe, and compound 21 is obtained in 93% yield. The 1-acetylated kinetic adduct 20 is formed in the initial stage of the reaction, and the migration from 20 to the thermodynamic 6-acetylated adduct 21 occurs during the reaction (as described in detail in Chapter 4). 

Experimental conditions were developed that require the use of indium(lll) triflate (1% mol) in the acetylation of anisole with AAN in combination with silver perchlorate in acetonitrile at 50°C. 3 The reaction gives para-methoxyacetophenone in 82% yield, and better results, namely, 96% yield, can be achieved by increasing the lithium perchlorate amount (from 25% to 100%) in nitromethane at 50°C for 1 h. The catalytic system is highly effective for the acetylation of electron-rich aromatic and... 

Table 3.8 Acetylation of (hetero) aromatics with AAN in the presence of indium(lll) triflate-lithium perchlorate mixture in nitromethane at 50°C for 1 h...

Anhydrous lithium salts are soluble in organic solutions which can be considered to be air-stable catalysts. The most common is lithium perchlorate which is generally used in solution in diethyl ether (LPDE) [9], nitromethane [15], and dichloro-methane [16]. Its catalytic role comes from the properties of the lithium cation [17] which gives rise to specific solute-Liinteractions modulated by complexation to appropriate solvents and counterions [18]. A recent proposal denies lithium catalysis and emphasizes electrostatic stabilization of the transition state by LPDE... 

Okada and Chiba [47] have proposed the application of thermomorphic multiphase systems to electrolysis. On mixing cyclohexane with nitromethane containing lithium perchlorate three phases result, with a cyclohexane-based thermomorphic phase separating the cyclohexane and nitromethane layers. Such systems have been shown to give excellent yields of cyclobutane derivatives formed by the anodic coupling of olefins (see Figure 5.2). 

Electrochemical [3 + 2] cycloaddition reactions in thermomorphic biphasic cyclohexane (c-Hex)/ lithium perchlorate (LPC)/ nitromethane (NM) solution... 

Also obtained by Friedel-Crafts acylation of 3-tert-butylphenol with acetyl chloride in the presence of hafnium triflate in 12 M lithium perchlorate in nitromethane (76%) [3349],... 

Also obtained by Fries rearrangement of 4-(N-acetylamino)anisole in the presence of lithium perchlorate and ytterbium triflate in nitromethane at 100° for 8 h [4086]. 

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