Lithium perchlorate in diethyl ether

A study of the Diels-Alder reaction was carried out by Earle et al. [42]. The rates and selectivities of reactions between ethyl acrylate (EA) and cyclopentadiene (CP) in water, 5 m lithium perchlorate in diethyl ether (5 m EPDE), and [BMIM][PE(3] were compared. The reactions in the ionic liquid [BMIM][PE(3] were marginally faster than in water, but both were slower than in 5 m EPDE [42, 43] (see Table 5.1-1 and Scheme 5.1-18). It should be noted that these three reactions give up to 98 % yields if left for 24 hours. The endo. exo selectivity in [BMIM][PE(3] was similar to that in 5 M EPDE, and considerably greater than that in water (Table 5.1-1). 

Acid catalyzed ionic Diels-Alder reactions in concentrated solutions of lithium perchlorate in diethyl ether [43]... 

Lithium trifluoromethanesulfonimide in acetone or diethyl ether as a safe alternative to lithium perchlorate in diethyl ether for effecting Diels-Alder reactions. Unexpected influence of the counterion on exo/endo selectivity [47]... 

Keywords imines derived from formylphosphonate undergo Diels-Alder reactions only in those cases which carry a strongly electron-withdrawing N-substituent. Lewis acidity, solvent effect, lithium perchlorate in diethyl ether... 

Dramatic rate accelerations of [4 + 2]cycloadditions were observed in an inert, extremely polar solvent, namely in 5 M solutions of lithium perchlorate in diethyl ether (= 532 g LiC104 per litre ). Diels-Alder additions requiring several days, 10 — 20 kbar of pressure, and/ or elevated temperatures in apolar solvents are achieved in high yields in some hours at ambient pressure and temperature in this solvent (P.A. Grieco, 1990). Also several other reactions, e.g., allylic rearrangements and Michael additions, can be drastically accelerated by this magic solvent. The diastereoselectivities of the reactions in apolar solvents and in LiClOi/Et O are often different or even complementary and become thus steerable. 

The kinetics of high-pressure cycloaddition reactions of tropone with dienophiles and enophiles have been reviewed.254 The Diels-Alder reaction of 9,10-dimethylanthracene with acrylonitrile has been investigated at high pressure in acetonitrile and in ethereal solutions of lithium perchlorate.255 The combination of high pressure and a solution of lithium perchlorate in diethyl ether is an excellent reaction rate accelerator in 4 + 2-cycloaddition reactions.256... 

Lithium perchlorate in diethyl ether has also been reported to accelerate Diels-Alder reactions significantly and this system has been applied to obtain Diels-Alder adducts that were inaccessible via conventional means [213-219]. A linear dependence of kobs on [Li+] is observed for the Diels-Alder reaction of DMA with acrylonitrile in LiC104-Et20 solution, while a second-order dependence of koba on [Li+] is involved for the reactions with fumaronitrile and dimethyl acetylenedi-carboxylate [216]. This suggests the possible contribution of Li -catalyzed electron transfer step in the Diels-Alder reaction as the case of Mg +-catalyzed Diels-Alder reaction in Scheme 12. However, such an electron transfer mechanism has not been confirmed in the Li -catalyzed Diels Alder reactions. 

The cyclocondensation of x-aminoaldehydes 17 and 6 (see p 2931) with Danishefsky s diene 1 can be efficiently catalyzed by 0.5 M lithium perchlorate in diethyl ether with typical predominance of. jyM-pyrones 43 for monoprotected aldehydes and twm -pyrones 44 for Ar,N-diprotected7S. Similarly, diene 42 reacts with x-aminoaldehyde 17k to provide anti-AA, almost exclusively, when catalyzed by a 3.0 M lithium perchlorate solution. 

The use of highly polar media such as water clearly assists the Diels-Alder reaction, and similar rate enhancement has been observed in other reactions. Grieco et al. showed that 5.0 M lithium perchlorate in diethyl ether is an effective medium for these reactions, There is a problem, however, because weak acids in highly polar media such as this become strong acids, and protonation of dienes in intramolecular reactions can lead to diene isomerization that is competitive with cycloaddition. 25 Grieco and Kaufman found that for such... 

The Friedel-Crafts alkylation of furans with P-nitrostyrene was promoted by lithium perchlorate in diethyl ether (13TL6776). 

High regioselectivity has been observed for addition of silyl enol ethers to a,p-unsaturated aldehydes and ketones, promoted by lithium perchlorate in diethyl ether. Potassium enolates of acyclic y-alkoxy-a-methyl pentanoates can be alkylated with allylic and benzylic halides with high 2,3-syn selectivity. The results have been rationalized in terms of non-chelated (for potassium enolates) and chelated (for lithium enolates) transition states. 

Lithium perchlorate in diethyl ether (LPDE), which is used widely in organic synthesis, is an ionic liquid when the lithium perchlorate concentration is greater than 4.25 M because all of the ether is complexed to Li+. The primary means by which LPDE operates is via Li+ catalysis. - ... 

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