Ether cleavage catalysts, Lewis acids

Looking for a more efficient catalyst to carry out this reaction thus became the most important issue. To achieve this, a large number of common Lewis acids were screened, including the halides of aluminum, iron, zinc, titanium, zirconium, nickel, copper, tin and lead. A number of these compounds did show activities as ether cleavage catalysts. The most effective catalysts were the halides... 

Table 22.1 Lewis acids as ether cleavage catalysts...

Diels-Alder reactions.1 The diene undergoes uncatalyzed [4+2]cycloaddition with very reactive dienophiles, but generally a Lewis acid catalyst (ZnCl, or C2H5A1C12) is required. Thus, the catalyzed reaction of 1 with methyl acrylate proceeds at 0° to afford, after silyl ether cleavage, the cycloadducts 2 and 3. 

Tris(pentafluorophenyl)borane [B(CgFj)3], is a powerful and selective Lewis acid catalyst used in many reactions in organic chemistry [1 ]. Parks and Piers [5] found that B(CgFj)3 catalyzes the hydrosilylation of carbonyl compounds. The silylation of alcohols with the formation of Ft as the only by-product [6] and the cleavage of silyl ether and ether bonds catalyzed by B(C F5)3 [7, 8] provide an... 

An improved ligand design by Manioka, Saito and Yamamoto has led to a catalyst that is effective for allyl vinyl ethers that are unsubstituted on the vinyl group [27]. This was a serious limitation of the BINOL-derived catalyst 98 which induced only C-O bond cleavage with these substrates (Table 1, entry 1). The ligand (f )-115 was prepared in six steps from (/ )-BINOL and was reacted with trimethylaluminum to give C3 symmetrical Lewis acid Five substituted catalysts were prepared and as... 

BE3 -OEt2 easy-to-handle and convenient source of BF3 Lewis acid catalyst promotes epoxide cleavage and rearrangement, control of stereoselectivity BF3 MeOH esterification of aliphatic and aromatic acids cleavage of trityl ethers)... 

Exclusive cleavage of the cycloalkyl carbon-oxygen bond occurs on treatment of cycloalkyl methyl and ethyl ethers with acetyl chloride in the presence of a Lewis acid catalyst. 

The coordination and organometallic chemistry of zirconium and hafnium are surveyed for the year 1991.107,108 There is useful material in a review of homogeneous Group 4 metallocene Ziegler-Natta catalysts, a review of the coordination chemistry of cyclopentadienyl titanium carboxylate and related complexes O and a review of bis(cycIopentadienyl)zirconium(IV) or hafnium(IV) complexes with Si-, Ge-, Sn-, N-, P-, As-, Sb-, 0-, S-, Se-, Te- or transition metal-centred anionic ligands. Cationic zirconocene or hafiiocene complexes serve as Lewis acids with unique reactivities, they are active for C-F bond activation, coordinative activation of ether linkages, carbonyl activation and C-O bond cleavage. New synthetic methods based on the... 

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