Zirconium acetyl chloride

AICI3 is a moisture-sensitive and strong Lewis acid. It is a first choice for Friedel-Crafts-type reactions, which provide numerous important transformations in laboratory and industry. It can also be applied to the transformation of alkenes to ketones via alkylaluminum halides.303 Hydrozirconation of an olefin and subsequent transmetalation from zirconium to aluminum gives the corresponding alkylaluminum dichloride, and the subsequent acetylation by acetyl chloride affords the corresponding ketone in high yield (Scheme 66). 

In a brief preliminary note Heine, Cottle, and Van Mater reported comparative results showing that zirconium tetrachloride is generally superior to aluminum chloride for the Friedel-Crafts p-acetylation of toluene with acetyl chloride. However, the results were less consistent with ZrCl, than with AICI3. Gore and Hoskins studied the Friedel-Crafts reaction of benzoyl chloride with anthracene in ethylene dichloride at 0° in the presence of 14 different catalysts. The best yields of very pure 9-benzoylanthracene were with zirconium tetrachloride (97% yield after lihrs.) and with aluminum chloride (86% yield after U hrs., 99% yield after 99 hrs.). 

Certain cyclic ketones dissolved in acetyl chloride when added to zirconium tetrachloride dissolved in the same solvent gave a precipitate of composition 2 1 ketone ZrCl 4. The following properties were recorded for the adducts anthrone, green, m.p. >325°C 10-nitroanthrone, green,... 

ZnCU Zinc chloride, 6 154 7 168 ZrBn Zirconium bromide, 1 49 Zr(C6H702)4 Zirconium acetyl-acetonate, 2 121 10-hydratc, 2 121... 

The acylation of arenes with alcohols has been shown to be possible using a palladium chloride catalyst in the presence of f-butylhydroperoxide. In 2-arylpyridines, substitution is directed to the ortho-position and, after initial paUadation, the formation of intermediate (59) is likely before reductive elimination yields the acylated product. The regioselective acetoxylation of indoles, at the 3-position, has been achieved using the palladium-catalysed reaction with phenyliodonium acetate. 3-Acyl indoles may also be prepared using acetyl chlorides with zirconium tetrachloride as a Lewis acid catalyst. 

Chakraborti, A. K. and Gulhane, R. 2004. Zirconium(IV) chloride as a new, highly efficient, and reusable catalyst for acetylation of phenols, thiols, amines, and alcohols under solvent-free conditions. Synlett. 4 627-630. 

In an early paper, the formation of products of lower chloride zirconium ratios, as compared to the moles of acetyl chloride employed with zirconium tetra-tert-butoxide, was ascribed to steric effects. However, in a careful re-examination, the reactions between metal fert-butoxides and acetyl halides have been found " to follow an entirely different course. For example, the reaction between zirconium tertiary butoxide and acetyl chloride was slow, and complete replacement of even one mole of tertiary butoxo group was not achieved the equimolar reaction product had the average composition, ZrClo.7(OBu )3 3. On the basis of further reaction of zirconium chloride tertiary butoxide with acetyl chloride it appeared that a side reaction occurred and instead of higher chloride alkoxides, mixed-alkoxide acetates were formed ... 

Water-incompatible halides, such as acetyl chloride, may be highly corrosive to zirconium. They are not stable. They react violently with water. There is no chance of water to be present in this type of halide, which is the most undesirable organic for zirconium, and maybe other metals, to handle. 

Glycosyl halides (7a-e) were stereoselectively transformed into l,2-tra s-thio-glycoses by i) (8a-d, 8j) a two-step procedure via the pseudothiourea derivatives [9,10a] the substitution of halide by thiourea is mostly a S l-type reaction since acetylated 1-thio-a-D-mannose (8b) was obtained from acetobromoman-nose (7b) [9cj ii) (8e-i) using thiolates in protic and aprotic solvents [10], or under phase transfer catalysis conditions [11]. Another approach involved the reaction of thioacetic acid with 1,2-trans-per-O-acetylated glycoses catalyzed with zirconium chloride [12]. The 1,2-trans-peracetylated 1-thioglycoses (8e-h) were obtained in high yield. No anomerized products could be detected in these reactions (Fig. 1). 

Zirconium chloride - catalyzed condensation of 2,3 4->6-tetra-0-acetyl-1-thio- C-D-glucopyranose with 1,3,4 6-tetrabenzyl- -D-fructo... 

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