Arenes, zinc-acetic acid

The key starting compound is the mono nitro derivative of calix[4]arene 4, which was obtained via a single-step reaction with 10 equivalents of 63% HNO3 in a mixture of dichloromethane and glacial acetic acid in less than 5 min in 94% yield according to the literature method. Compound 4 converted to bisphthalonitrile derivative 5 by the given method in 59% yield. Ball-type ZnPc 6 was prepared from 5 and zinc acetate in 1-pentanol in the presence of DBU. Hexanuclear ball-type ZnPc 8 was obtained by the reaction of 6 with 7 in a mixture of NaOH, MeOH, THF, and activated zinc powder with a yield of 55%. 

Amination of arenes. With Znl2 as the catalyst, the reagent is an adequate electrophilic reagent for many arenes. The products are cleaved in one step to provide the amines by treatment with zinc dust in acetic acid. 

The dioxygen oxidation system utilizing a dinuclear j,-oxo iron(III) complex catalyst (HB(pz)3)2Fe( X-0)(X)2, (X = acetate or hexafluoroacetylacetonate) has been reported [92, 93]. This system also needs zinc powder as an electron donor and acetic acid as a proton source. Different from the Gif system, the hydroxylation of arene proceeds in the latter case, suggesting that the reactive intermediate of this system is different from that of the Gif system. Replacing X in the complex by hexafluoroacetylacetone enhances the reaction rate and the turnover frequently of benzene hydroxylation at room temperature reaches more than 10. Typical results are shown in eq. (9). Unfortunately, these dinuclear iron complexes are not so stable for elongated reaction time and decomposes to afford an inert complex, (HB(pz)3)2Pe which makes further mechanistic investigation difficult. 

Readily available functionalized aryl siloxanes are also viable cross-coupling partners for Pd(dba)2-catalyzed allylic arylations. A mixture of 5% Pd(dba)2, allylic halide, and in situ-generated aryl zinc reagent produces allylated arenes in high yield. Aryl boronic acids have been converted to allylated arenes as well. Diastereoselective intramolecular Stille-type coupling of two allylic moieties (aUylic acetate and allylic stannane) has been performed in high yield to produce the key intermediate in the synthesis of racemic 10-ep/-elemol (eq 19). ... 

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