Lithium perchlorate catalyst

Sulfinyldiene 40 reacts, regio- and stereo selectively, with methylacrylate in the presence of a catalyst, affording carbomethoxycyclohexene derivatives [45]. Among the catalysts examined, the best was lithium perchlorate used as a suspension in DCM it gave only endo isomers in 70% yield in a 96 4 d.e. ratio (Equation 3.11). 

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. 

In most instances these catalysts were not satisfactory in terms of yield, range of substrates and turnover numbers of the catalyst. Additionally, they were mostly efficient only in the case of activated aromatics. In order to develop also Friedel-Crafts acylations of less activated or even deactivated arenes, a new generation of catalysts had to be developed. Here, particularly bismuth(III) triflate [33] and hafnium(IV) triflate in the presence of lithium perchlorate [34] or triflic acid [35] are effective, alternative catalysts actually acylating benzene, toluene and halobenzenes. 

A pair of papers describe the use of lanthanide triflates, in preference to unstable lithium perchlorate, as catalysts in heterodiene synthesis <95SL233> <95SYN1195>, as was also noted in <95TL(36)8977> and Scheme 14. 

Azabutadienes have also been reported to react with dimethylmaleate <1995TL8977> with significant rate enhancement using LiNTf2. However, it has been noted that the use of lanthanide triflates as catalysts can be preferable to the unstable lithium perchlorate <1995SL233>. 

Easily dissociable, highly polar organic compounds were used occasionally as cationic initiators. Thus, triphenyl methyl chloride (77), triphenyl methyl chloromercurate (72), alkyl, acyl, and nitronium tetra-fluoro borates (13), silver perchlorate (77, 14), lithium perchlorate (75), acetyl, benzoyl, and tert.-butyl perchlorate (16) and acetyl fluoroborate (16) were mentioned at various times as catalysts for cationically initiable monomers. 

If the reactions are carried out in a nitrile as solvent, rather than dichloromethane, using triflic acid as catalyst, a modified Ritter reaction takes place, and the intermediate nitrilium ion traps the liberated amine, forming an amidine (Scheme 67). In an earlier reaction cf. Scheme 67) the lithium perchlorate catalyzed reaction of sulfenyl chlorides with alkenes in the presence of nitriles had also given l-amido-2-sulfenyl adducts. Ritter products are also obtained in good yields by anodic oxidation (Pt or C, 1.2-1.4 V) of disulfides in acetonitrile, in the presence of excess alkene, using B114NBF4 as supporting electrolyte (Scheme 68). ... 

Chiral amino alcohols can be prepared by reaction of chiral epoxides with amines. Enantiopure (25, 3.R)-2,3-epoxy-3-phenylpropanol anchored to Merrifield resin has been used for ring-opening with secondary amines in the presence of lithium perchlorate to afford polymer-supported chiral amino alcohols 47 (Eq. 18) [56], By analogy, (2i ,35)-3-(cis-2,6-dimethylpiperidino)-3-phenyl-l,2-propanediol has been anchored to a 2-chlorotrityl chloride resin (48). Although this polymer had high catalytic activity in the enantioselective addition of diethylzinc to aldehydes, the selectivity of the corresponding monomeric catalyst was higher (97 % ee) in the same reaction. 

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-... 

Free-ion attack is more likely for sterically hindered R. The ion CH3CO has been detected (by IR spectroscopy) in the liquid complex between acetyl chloride and aluminum chloride, and in polar solvents, such as nitrobenzene but in nonpolar solvents, such as chloroform, only the complex and not the free ion is present." In any event, 1 equivalent of catalyst certainly remains complexed to the product at the end of the reaction. When the reaction is performed with RCO+SbFg, no catalyst is required and the free ion" " (or ion pair) is undoubtedly the attacking entity." The use of LiC104 on the metal triflate-catalyzed Friedel-Crafts acylation of methoxy-naphthalene derivatives has been examined, and the presence of the lithium salt leads to acylation in the ring containing the methoxy unit, whereas reaction occurs in the other ring in the absence of lithium salts." Note that lithium perchlorate forms a complex with acetic anhydride, which can be used for the Friedel-Crafts acetylation of activated aromatic compounds." ... 

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. 

Anisole can be acylated with acetic anhydride in 99% yield (6.12). Yttterbium triflate can also be used. The yields are low when there is no activating group in the ring. The rate is accelerated by the addition of lithium perchlorate.56 Acylation of alcohols works well with 1 mole% of scandium triflate as a catalyst (6.13).57 The less toxic toluene has also been used as the solvent in such acylations. The... 

Mukaiyama, T., Suzuki, K., Han, J. S., and Kobayashi, S. 1992. A novel catalyst system, antimony(V) chloride-lithium perchlorate (SbCls-LiClOJ, in the Friedel-Crafts acylation reaction. Chem. Lett. 435 38. 

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