Chem
Volume 7, Issue 3, 11 March 2021, Pages 555-605
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Review
Transition-metal-catalyzed C–H allylation reactions

https://doi.org/10.1016/j.chempr.2020.10.020Get rights and content
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The bigger picture

The synthetic utility of the “allyl” unit is well understood and is often encountered in flavor and fragrance industries, pharmaceuticals, supra-molecular assemblies, and synthetic bioactive natural products. Incorporation of an allyl moiety into a complex organic framework enhances the utility of the overall synthetic application due to its late-stage nature. Direct C–H allylation assures selective productive formation by limiting extra steps and precluding the by-product formation. The asymmetric variant especially contributes toward the ligand and catalyst designs for asymmetric functionalization. Employing inexpensive base metals, activation of inert C–C bond of allyl synthon, selective remote functionalization, utilizing unusual allyl coupling partners, designing exciting ligands for asymmetric synthesis, etc., are some of the attractive outcomes from this domain. Owing to the versatility for further transformations, C–H allylation strategies have emerged as a promising synthetic transformation.

Summary

Allylation reactions are one of the most fundamental and productive C−C bond-forming transformations, as the allyl group can provide a useful handle for further manipulation. Apart from this, their omnipresence in bioactive species makes them invaluable in medicinal science and pharmaceutical industries. Pioneered by Tsuji and Trost, a myriad of synthetic strategies of allylation reactions have evolved significantly over the last few decades. With the emergence of site-selective C–H activation, the perimeter of allylation reactions has extended in different latitudes. C–H activation has averted the over dependency on traditional approaches and has circumvented its major drawbacks. With the present state of knowledge, C–H allylation reactions not only have precluded the need for pre-functionalized substrate and activated allylating reagents but it is also now apparent that they trigger the allylic selectivity of an unsaturated hydrocarbon under proper metal-ligand combination. This review aims to embrace all the aspects of transition-metal-promoted C–H allylation reactions.

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Keywords

transition metal catalysis
C–H allylation
proximal to distal
asymmetric catalysis
photocatalysis

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