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Mg for B: An atom-economical one-pot synthesis by direct magnesium insertion in the presence of B(OBu)3 and LiCl allows a broad range of functionalized (hetero)aryl and alkenyl bromides to be converted into magnesium diorganoboronates 2, which undergo Suzuki–Miyaura cross-coupling reactions with various aryl (pseudo)halides (see scheme). Both aryl groups of 2 are transferred and furnish the products in good to excellent yields.
[Credit: Angewandte Chemie, DOI 10.1002/anie.201103022] |
The Suzuki reaction – which involves the use of palladium to catalyze the cross-coupling of organoboron compounds with organic halogen-containing molecules – makes it possible to link carbon atoms together in a very straightforward way. The products of the reaction can then be utilized for the construction of a virtually unlimited number of organic substances. The Suzuki reaction thus forms the basis for the synthesis of novel drugs and innovative materials. Akira Suzuki was awarded the Nobel Prize in Chemistry for his discovery of the reaction that bears his name.
Knochel and his team were hoping to extend the applicability of the reaction by finding an easy, economical and general way to synthesize the necessary organoboron compounds so that they could be used in Suzuki reactions without further purification. "We were able to optimize the process in such a way that the boronates can be made in a one-pot reaction", says Christoph Sämann, who made a major contribution to the study. "The method works well under very mild conditions, is compatible with many different functional groups and can therefore be applied to a wide range of compounds."
In contrast to the organoboronates that have been used so far, the products generated via the new synthetic route have two organic groups attached to the boron atom, and both can be transferred, without loss, in the course of the subsequent Suzuki reaction. "This significantly improves overall yields, making the reaction much more economical," says Knochel. "The new reaction also produces less waste, which is an especially important consideration in industrial applications."
[suwe]