Hafnium triflate

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. 

Regioselective direct acylation of phenol and naphthol derivatives with acid chlorides was achieved by using hafnium triflate, Hf(OTf)4 (5 to 20 mol%), as a catalyst (equations 40 and 41) 5. 

Reactions with otP-Unsaturated Ketones, Nitriles and Nitro-Compomds Such reactions are usually effected using acid (see below), or one of a number of mild Lewis acids, such as scandium iodide (with microwave heating), indium bromide " or hafnium triflate, and can be looked on as an extension of the reactions discussed in 20.1.1.6. In the simplest situation, indole reacts with methyl vinyl ketone in a conjugate fashion in acetic acid/acetic anhydride. ... 

Hafnium triflate has also been used for acylation and alkylation of aromatic compounds.64 It has also been used in aromatic nitration in a process (6.18) that eliminates the usual waste acid from such reactions.65 The products are intermediates in the synthesis of toluene diisocyanates used in making polyurethanes. The catalyst could be reused with... 

A dramatic acceleration of benzene acylation is also observed by using a similar catalyst consisting of a combination of hafnium triflate and triflic acid. While in the benzoylation of benzene with BC, low yields of benzo-phenone (BP) (5%-10%) are obtained in the presence of hafnium triflate (5% mol) or triflic acid (5% mol), a 77% yield is obtained when combining hafnium triflate (5% mol) with triflic acid (5% mol). The yield is improved to 82% when hafnium triflate and triflic acid are used in higher quantity (10% mol) a further increase of the catalyst amount does not improve the... 

Table 3.6 Acylation of aromatics with acyl chlorides promoted by hafnium triflate-triflic acid mixture...

Kobayashi, S. and Iwamoto, S. 1998. Catalytic Friedel-Crafts acylation of benzene, chlorobenzene, and fluorobenzene using a novel catalyst system, hafnium triflate and trifluoromethanesulfonic acid. Tetrahedron Lett. 39 4697 700. 

The Fries rearrangement of phenyl- and 1-naphthyl esters can be efficiently performed in the presence of hafnium triflate. The method is based on the one previously described for the Friedel-Crafts acylation of arenes with acyl chlorides. The reaction occurs in toluene-nitromethane mixtures at 100°C for 6 h. Several examples of this Fries isomerization with synthetic application are reported in Table 5.5. In all cases, complete regioselectivity is obtained, and 2-acylated phenol or naphthol derivatives are isolated in good yields. 

Table 5.5 Hafnium-triflate-promoted Fries rearrangement of phenyl esters...

Hafnium triflate has been used for catalytic Friedel-Crafts acylation of aromatic rings [25]. The same catalyst has been found to be effective for heteroaromatics such as furan and pyrrole (58) (Equations 19 and 20) [26]. The reaction of furan with acetic anhydride gave 2-acetylfuran exclusively, whereas that of pyrrole (58) gave a mixture of 2- and 3-acetylpyrroles. 

Preparation by Fries rearrangement of m-methoxyphenyl cyclohexanecarboxylate in a nitromethane/toluene mixture in the presence of hafnium triflate/hthium perchlorate for 6 h at 50°. 

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],... 

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