The linear or branched allyl moieties on aromatic rings are well-known as ubiquitous structural motifs found in a range of natural products and medicinally relevant molecules. They also represent an important class of organic intermediates for the transformation of an olefin group into many useful functional groups. Established methods for the installation of allylic groups rely primarily on nucleophilic substitution or transmetalation of aryl metal complexes to allyl electrophiles, Lewis acid-mediated Friedel−Crafts allylation of electron-rich arenes, and Tsuji−Trost allylation reactions with π-allyl species. Complementing previous protocols, the transition metal-catalyzed allylation reactions via C−H activation strategy using various allylic surrogates like allylic acetates, allylic carbonates, allylic phosphonates, allylic halides, allylic alcohols, vinyl oxiranes, allenes, 1,3-dienes, and others have recently emerged as a powerful tool for creating the corresponding allyl, crotyl and prenyl moieties. This review, which includes all reported methods in the literature until the beginning of 2017, focuses on recent progress on direct allylation reactions of aromatic and vinylic C(sp 2 )−H bonds with allylic sources and various transition metal catalysts.

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The rhodium(III)-catalyzed redox-neutral coupling reaction of N-acyl ketimines generated in situ from 3-hydroxyisoindolinones with various activated olefins is described. This approach leads to the synthesis of bioactive spiroisoindolinone derivatives in moderate to high yields. In the case of internal olefins such as maleimides, maleates, fumarates, and cinnamates, spiroindanes were obtained by the [3 + 2] annulations reaction. In sharp contrast, acrylates and quinones displayed the β-H elimination followed by Prins-type cyclization furnishing spiroindenes. The synthetic compounds were evaluated for in vitro anticancer activity against androgen-sensitive human prostate adenocarcinoma cells (LNCaP), human prostate adenocarcinoma cells (DU145), human endometrial adenocarcinoma cells (Ishikawa), human breast cancer cell (MCF-7), and triple negative human breast cancer cells (MDA-MB-231). Notably, quinone-containing spiroindenes displayed potent anticancer activity about 2- to 3-fold stronger than that of anticancer agent doxorubicin.

The rhodium‐catalyzed selective cyanation of CH bonds of indolines and indoles with N‐cyano‐N‐phenyl‐para‐methylbenzenesulfonamide is described. This protocol offers a facile access to C‐7 cyanated indolines and C‐2 cyanated indoles with high site selectivity and excellent functional group tolerance.magnified image

The rhodium(III)-catalyzed cross-coupling reaction of 8-methylquinolines and maleimides is described. In contrast to the C(sp(2))-H functionalization, a first catalytic functionalization of sp(3) C-H bonds with maleimides is reported. This protocol provides a facile access to various succinimide scaffolds on 8-methylquinolines via a direct C-H cleavage approach.

Palladium-catalyzed decarboxylative acylation of highly substituted indolines with α-keto acids via C-H bond activation is described. This protocol provides efficient access to C7-carbonylated indoles known to have diverse biological profiles.

The transient directing group promoted C(sp)-H functionalization of benzaldehydes with anthranils by a cationic rhodium(III) catalyst is described. Notably, anthranils have been used as both transient directing groups and amination sources to afford 2-acyl acridines through direct C-H amination followed by acid-mediated cyclization. A range of substrate scopes and functional group tolerance were observed.

The weakly coordinating ketone group directed C-H functionalizations of chromones, 1,4-naphthoquinones, and xanthones with various maleimides under rhodium(III) catalysis are described. These protocols efficiently provide a range of succinimide-containing chromones, naphthoquinones, and xanthones with excellent site selectivity and functional group compatibility. All synthetic compounds were screened for in vitro anticancer activity against human breast adenocarcinoma cell lines (MCF-7). In particular, compounds 7aa and 7ca with a naphthoquinone scaffold were found to be highly cytotoxic, with an activity competitive with anticancer agent doxorubicin.