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Preparation of Polyfunctional Arylmagnesium, Arylzinc, and Benzylic Zinc Reagents by Using Magnesium in the Presence of LiCl

Authors

  • Fabian M. Piller,

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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  • Albrecht Metzger Dipl.-Chem.,

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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  • Matthias A. Schade,

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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  • Benjamin A. Haag Dipl.-Chem.,

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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  • Andrei Gavryushin Dr.,

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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  • Paul Knochel Prof. Dr.

    1. Department Chemie und Biochemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München (Germany), Fax: (+49) 89-2180-77680
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Abstract

The presence of LiCl considerably facilitates the insertion of magnesium into various aromatic and heterocyclic bromides. Several functional groups, such as -OBoc, -OTs, -Cl, -F, -CF3, -OMe, -NMe2, and -N2NR2, are well tolerated. The presence of a cyano group leads in some cases to competitive reduction of the organic halide to the corresponding ArH compound. The presence of sensitive groups such as methyl or ethyl ester is tolerated upon in situ trapping of the intermediate magnesium reagent with ZnCl2. This method can also be applied to the preparation of functionalized benzylic zinc reagents from benzylic chlorides. In the case of di- or tribromoaryl derivatives, directing groups such as -OPiv, -OTs, -N2NR2, or -OAc orient the zinc insertion (Zn/LiCl) to the ortho-position, while the reaction with Mg/LiCl or Mg/LiCl/ZnCl2 leads to regioselective insertion into the para-carbon–bromine bond. Large-scale experiments (20–100 mmol) for all of the metalation procedures are described.

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