Lithium perchlorate-diethyl ether

During 1989-93 lithium perchlorate iethyl ether (LiC104 EtiO, LP-DE) was studied as a reaction medium in organic synthesis when it was observed that cycloadditions, sigmatropic rearrangements, Michael additions and aldol condensations carried out in LP-DE occurred quickly and selectively under mild reaction conditions [33]. In addition, LP-DE allowed the reaction and subsequent work-up to be carried out under essentially neutral conditions. 

Initially the LP-DE effect was ascribed to the high internal pressure generated by the solubilization of the salt in diethyl ether [34]. Today the acceleration is explained in terms of Lewis-acid catalysis by the lithium cation [35]. The contribution of both factors (internal pressure and lithium cation catalysis) has also been invoked [36]. 

LP-DE has a weaker catalytic activity than BF3-Et20, AICI3 and TiCU because the Lewis acidity of the lithium cation is moderated by complex-ing with diethyl ether and perchlorate anion [37], but it becomes a highly oxophilic Lewis acid when concentrated solutions are used [38]. The concentration of LP-DE is therefore sometimes essential for the success of the reaction. 

Diels-Alder Reaction in Non-Aqueous Polar Systems 

LP-DE also promotes and accelerates intramolecular Diels-Alder reactions of low reactive polyenones. The use of a catalytic amount of camphorsulfonic acid (CSA) further accelerates the cycloaddition and enhances the diastereo-selectivity [41]. Table 6.7 illustrates the effect of CSA on the intramolecular Diels-Alder reaction of 2-methyl-l,7,9-decatrien-3-one. 

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Dramatic rate acceierations of Dieis-Aider reactions in 5m lithium perchlorate-diethyl ether the cantaridin problem reexamined [34]... 

Acid catalyzed intramolecular Diels-Alder reactions in lithium perchlorate-diethyl ether acid promoted migration of terminal dienes prior to [4 + 2] cycioaddition in conformationally restricted substrates [101]... 

A safe recyclable alternative to lithium perchlorate-diethyl ether mixture [54]... 

Lithium perchlorate-diethyl ether promotes the chemo- and regioselective conversion of epoxides to carbonyl compounds (e.g., 126 127), a reaction which is thought to proceed via... 

Grieco investigated the intramolecular Diels-Alder reaction of imi-nium ions in polar media such as 5.0 M lithium perchlorate-diethyl ether and in water129 to form carbocyclic arrays. They showed that water as the solvent provided good-to-excellent yields of tricyclic amines with excellent stereocontrol (Eq. 12.58). 

Iodine(VII) oxide Diethyl ether Lithium perchlorate Diethyl ether... 

Earle, M. J., McCormac, P. B. Seddon, K. R. Diels-Alder reactions in ionic liquids a safe recyclable green alternative to lithium perchlorate-diethyl ether mixtures. Green Chem., 1999, 1(1), 23-25 Doherty, S. Goodrich, P. Hardacre, C. et al. Marked enantioselectivity enhancements for Diels-Alder reactions in ionic liquids catalysed by platinum diphosphine complexes. Green Chem., 2004, 6(1), 63-67. 

The Diels-Alder reaction is an important and widely used reaction in organic synthesis (Sauer and Sustmann, 1980), and in the chemical industry (Griffiths and Previdoli, 1993). Rate enhancement of this reaction has been achieved by the use of solvents such as water, surfactants, very high pressure, lithium amides, alkylammonium nitrate salts, and macrocyclic hosts (Sherman et ak, 1998). Diels-Alder reactions can be ran in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfo-nate, l-butyl-3-methylimidazolium hexafluorophophate, l-butyl-3-methylimidazolium tetrafluoroborate, and l-butyl-3-methylimidazolium lactate). Rate enhancements and selectivities are similar to those of reactions performed in lithium perchlorate-diethyl ether mixtures. 

Grieco, P. A. Nunes, J. J. Gaul, M. D. Dramatic rate accelerations of Diels-Alder reactions in 5 M lithium perchlorate-diethyl ether The cantharidin problmi reexamined, J. Am. Chem. Soc. 1990,112,4595-4596. 

The kinetics of the acid-catalysed isomerization of (—)-menthone (140) to (+ )-isomenthone (141) using hydrogen chloride and perchloric acid in lithium perchlorate-diethyl ether solution have been measured. 

Aminoalkyl and Related Acids. - Further development of the classical three component approach to aminoalkylphosphonates (the Kabachnik-Fields reaction) has been reported. The reaction of aldehydes, hydroxylamines and dimethyltrimethylsilyl phosphite using lithium perchlorate/diethyl ether as a catalyst gives N-trimethylsilyloxy-a-aminophosphonate derivatives. The catalytic activities of various lanthanide triflates as well as indium trichloride have been examined for the Kabachnik-Fields type reactions of aldehydes, amines and the phosphorus nucleophiles HP(0)(0Et)2 and P(OEt)3 in ionic liquids. TaCb-Si02 has been utilized as an efficient Lewis acid catalyst for the coupling of carbonyl compounds, aromatic amines and diethyl phosphite to produce a-... 

The mildness of the lithium perchlorate-diethyl ether medium may be illustrated by the outcome of the reaction of aldehyde (7) in 5.0 M LPDE with 2.3 equivalents of allyltrimethyltin at ambient temperature (Scheme 6.3.4). After 4 h, a 77% yield of the differentially protected triol (8) was obtained as a single diastereomer. The use of conventional Lewis acids (e.g. TiCU, SnCU) in methylene chloride to bring about the above transformation leads to an extensive decomposition even at -78 °C. 

See Halogens, or Interhalogens, above Chromy 1 chloride Organic solvents Fluorine nitrate Organic materials Hydrogen peroxide Diethyl ether lodine(Vll) oxide Diethyl ether Lithium perchlorate Diethyl ether Nitric acid Diethyl ether Nitrosyl perchlorate Organic materials Nitryl perchlorate Organic solvents Ozone Diethyl ether... 

Allylstannanes undergo similar reaction with a-alkoxy aldehydes under Lewis acid catalysis. The treatment of 464 with allyl tri- -butylstannane in the presence of either MgBr2 Et20 [150] or lithium perchlorate-diethyl ether [153] furnishes protected syn-dio 468 with a dia-stereoselectivity of at least 25 1. This intermediate has been carried on to TBS-protected L-( — )-rhodinose (302) in an overall yield of 46% starting from (9-benzyl ethyl lactate 271b [150] (Scheme 69). 

Greico and Kaufman used a similar strategy, this time involving the Diels-Alder reaction of 3-vinylindole with an appropriately tethered imine, to construct the pentacyclic ebumamonine structure in a very efficient manner [108] (Scheme 65). At first attempt, the thermal Diels-Alder reaction of imine 307 in 1,2-dichlorobenzene at 180°C afforded the cycloadduct 308 in only 32% yield, and without the formation of ebumamonine (309). Next, cycloadditions under acidic conditions were examined. The optimal conditions were found to involve conducting the reaction at 5 M lithium perchlorate-diethyl ether with 0.1 equivalent of cam-phorsulfonic acid, thus affording the Diels-Alder product 308 in 96% yield. 

Hunt KW, Grieco PA. Oxabicyclo[3.2.1]octenes in organic synthesis-direct ring opening of oxabicyclo[3.2.1] systems employing silyl ketene acetals in concentrated solutions of lithium perchlorate-diethyl ether application to the synthesis... 

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