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Ellwart, Mario; Makarov, Ilya S.; Achrainer, Florian; Zipse, Hendrik; Knochel, Paul (2016): Regioselective Transition-Metal-Free Allyl-Allyl Cross-Couplings. In: Angewandte Chemie-international Edition, Vol. 55, No. 35: pp. 10502-10506
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Abstract

Readily prepared allylic zinc halides undergo S(N)2-type substitutions with allylic bromides in a 1:1 mixture of THF and DMPU providing 1,5-dienes regioselectively. The allylic zinc species reacts at the most branched end (gamma-position) of the allylic system furnishing exclusively gamma,alpha'-allyl-allyl cross-coupling products. Remarkably, the double bond stereochemistry of the allylic halide is maintained during the crosscoupling process. Also several functional groups (ester, nitrile) are tolerated. This cross-coupling of allylic zinc reagents can be extended to propargylic and benzylic halides. DFT calculations show the importance of lithium chloride in this substitution.