The Barbier reaction, a family of related transformations employing alkyl halides and carbonyl compounds in the presence of metal or metalloid to generate a new C-C bond, offers one of the most versatile methods for strategically introducing C-C connectivity in organic chemistry. The general applicability of Barbier reaction stems from the fact that it uses diverse elements from the periodic table (alkaline earth metals, transition metals, lanthanides or amphoteric elements) for in situ formation of a reactive nucleophilic species to attack carbonyls. Barbier conditions can be water-compatible, providing advantage over other C-C-forming reactions that employ water-sensitive organometallic species, such as organomagnesium or organolithium. Additionally, they are tolerant to various pre-existing functionalities in the substrate, thus largely circumventing the need for protection-deprotection steps in a linear synthesis. In the last decade, a resurgence in the application of Barbier reactions has occurred, especially in the context of natural product synthesis, where this transformation is quickly proving to be a powerful tool. Since multiple (bioactive) natural product families feature homoallylic alcohol motifs as part of their structures, Barbier reactions involving allyl halides and carbonyl compounds as precursors to generate such homoallylic alcohols are becoming a method of choice. This review focuses on selected cases where homoallylic alcohols are the resulting products and where the Barbier reaction is stereocontrolled, with emphasis on the stereocontrolling elements in synthesis design and the models employed to rationalize the observed stereochemical outcome.
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