We developed a novel phosphine-catalyzed Friedel–Crafts reaction of naphthols with para-quinone methides (p-QMs). This reaction provided a promising method for the synthesis of triarylmethanes, which widely exist in natural products and in molecules which have been shown to have biological and pharmacological activity.

Herein, we report a gold-catalyzed highly site-selective C(sp2)–H functionalization of unactivated arenes with α-aryl-α-diazoesters with electron-withdrawing substituents as induced groups on aryl rings. Furthermore, the induced groups are useful for further synthetic transformations.

Correction for ‘Phosphine-catalyzed Friedel–Crafts reaction of naphthols with para-quinone methides: expedient access to triarylmethanes’ by Tao Zhou et al., Org. Biomol. Chem., 2017, DOI: 10.1039/c7ob00911a.

AbstractCompared to the most popular directing-group-assisted strategy, the “undirected” strategy for C−H bond functionalization represents a more flexible but more challenging approach. Reported herein is a gold-catalyzed highly site-selective C(sp2)−H alkylation of unactivated arenes with 2,2,2-trifluoroethyl α-aryl-α-diazoesters. This protocol demonstrates that high site-selective C−H bond functionalization can be achieved without the assistance of a directing group. In this transformation, both the gold catalyst and trifluoroethyl group on the ester of the diazo compound play vital roles for achieving the chemo- and regioselectivity.

Metal carbenes, generated from the decomposition of diazo compounds by transition-metals, have a broad range of applications in organic synthesis. The progress of organic transformation via transition metal (such as Rh, Cu, Fe, Ag) carbenes has been well summarized in a few excellent reviews. This review will summarize gold-catalyzed transformations of α-diazocarbonyl compounds by highlighting the specificity and applicability of these diverse transformations such as X–H insertion, C–H functionalization, cyclopropanation, cycloaddition, and coupling reactions. In order to understand these reactions, the mechanistic rationale for selected examples is also provided.

In past decade, gold revealed more and more unique properties in carbene chemistry. It was disclosed in our recent communication (J. Am. Chem. Soc. 2014, 136, 6904) that gold carbenes have unprecedented chemo- and site-selectivity and ligand effect toward the functionalization of C–H bonds in phenols. In this full article, we report a comprehensively combined theoretical and experimental study on the mechanism of the insertion of gold carbenes into C–H and O–H bonds in phenol. It significantly revealed that the ligands have an important effect on C–H insertion and the reaction proceeds through a pathway involving the formation of an enolate-like intermediate. Moreover, two water molecules serving as a proton shuttle are believed to be the key issue for achieving chemoselective C–H functionalization, which is strongly supported by the DFT calculations and control experiments. It is the first time that a clear explanation is given about the prominent catalysis of gold carbenes toward C–H functionalization based on a theoretical and experimental study.

A concise synthesis of functionalized indene derivatives via the gold(I)-catalysed cascade C–H functionalization/conia-ene type reaction of electron-rich aromatics with o-alkynylaryl α-diazoesters has been developed. In this transformation, the gold catalyst not only catalysed the formation of the zwitterionic intermediate via intermolecular C–H functionalization but promoted the subsequent intramolecular 5-endo-dig cyclization via activation of alkynes. The reaction is characterized by high chemo- and site-selectivity, readily available starting materials, nice functional-group tolerance and mild reaction conditions.

Herein, a novel and efficient gold-catalyzed intermolecular C(sp2)–H functionalization (Friedel–Crafts alkylation) and aldol annulation strategy is presented. This cascade process allows the synthesis of a series of indanol and tetrahydronaphthalenol derivatives with two adjacent quaternary stereocenters. The attractive reaction features are the use of readily available starting materials, good diastereoselectivity, good functional-group tolerance and mild reaction conditions. Furthermore, preliminary results indicate that this transformation is amenable to enantioselectivitive synthesis with further chiral ligand screening and design.

It was recently reported that the gold-carbenes have an unprecedented catalysis toward the functionalization of C(sp2)–H bonds of aromatic compounds. However, the associated mechanisms of C(sp2)–H bonds inserted by gold-carbenes have not been comprehensively understood. We carried out a detailed mechanistic investigation of gold-carbene insertion into the C(sp2)–H bond of anisole by means of theoretical calculations and control experiments. It significantly reveals that the aromatic C(sp2)–H bond activation starts with the electrophilic addition of aromatic carbon toward the carbene carbon and subsequently followed the [1,3]-proton shift to form an enol intermediate. The rearrangement of enol proceeds through the mechanisms of proton transfer assisted by water molecules or enol intermediates, which are supported by our control experiments. It was also found that the C(sp3)–H insertions of alkanes by gold-carbenes proceed through a concerted process via a three-centered transition state. The further comparison of different mechanisms provides a clear theoretical scheme to account for the difference in aromatic C(sp2)–H and alkyl C(sp3)–H bond activation, which is instructive for the further experimental functionalization of C–H bonds by gold-carbenes.

An unprecedented direct C–H bond functionalization of unprotected phenols with α-aryl α-diazoacetates and diazooxindoles was developed. A tris(2,4-di-tert-butylphenyl) phosphite derived gold complex promoted the highly chemoselective and site-selective C–H bond functionalization of phenols and N-acylanilines with gold-carbene generated from the decomposition of diazo compounds, furnishing the corresponding products in moderate to excellent yields at rt. The salient features of this reaction include readily available starting materials, unprecedented C–H functionalization rather than X–H insertion, good substrate scope, mild conditions, high efficiency, and ease in further transformation. To the best of our knowledge, this is the first example of C–H functionalization of unprotected phenols with diazo compounds.

A facile technique involving a novel Lewis-acid-catalyzed tandem selective ring-opening of oxirane and Friedel–Crafts alkylation of 1H-indol-1-yl derived oxiranes was developed. The developed protocol affords functionalized [1,4]oxazino[4,3-a]indoles and 3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazines in up to 95% yield.

A facile technique involving a novel Lewis-acid-catalyzed tandem selective ring-opening of oxirane and Friedel–Crafts alkylation of 1H-indol-1-yl derived oxiranes was developed. The developed protocol affords functionalized [1,4]oxazino[4,3-a]indoles and 3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazines in up to 95% yield.

Herein, a novel and efficient gold-catalyzed intermolecular C(sp2)–H functionalization (Friedel–Crafts alkylation) and aldol annulation strategy is presented. This cascade process allows the synthesis of a series of indanol and tetrahydronaphthalenol derivatives with two adjacent quaternary stereocenters. The attractive reaction features are the use of readily available starting materials, good diastereoselectivity, good functional-group tolerance and mild reaction conditions. Furthermore, preliminary results indicate that this transformation is amenable to enantioselectivitive synthesis with further chiral ligand screening and design.

Metal carbenes, generated from the decomposition of diazo compounds by transition-metals, have a broad range of applications in organic synthesis. The progress of organic transformation via transition metal (such as Rh, Cu, Fe, Ag) carbenes has been well summarized in a few excellent reviews. This review will summarize gold-catalyzed transformations of α-diazocarbonyl compounds by highlighting the specificity and applicability of these diverse transformations such as X–H insertion, C–H functionalization, cyclopropanation, cycloaddition, and coupling reactions. In order to understand these reactions, the mechanistic rationale for selected examples is also provided.

A concise synthesis of functionalized indene derivatives via the gold(I)-catalysed cascade C–H functionalization/conia-ene type reaction of electron-rich aromatics with o-alkynylaryl α-diazoesters has been developed. In this transformation, the gold catalyst not only catalysed the formation of the zwitterionic intermediate via intermolecular C–H functionalization but promoted the subsequent intramolecular 5-endo-dig cyclization via activation of alkynes. The reaction is characterized by high chemo- and site-selectivity, readily available starting materials, nice functional-group tolerance and mild reaction conditions.

We developed a novel phosphine-catalyzed Friedel–Crafts reaction of naphthols with para-quinone methides (p-QMs). This reaction provided a promising method for the synthesis of triarylmethanes, which widely exist in natural products and in molecules which have been shown to have biological and pharmacological activity.

In past decade, gold revealed more and more unique properties in carbene chemistry. It was disclosed in our recent communication (J. Am. Chem. Soc. 2014, 136, 6904) that gold carbenes have unprecedented chemo- and site-selectivity and ligand effect toward the functionalization of C–H bonds in phenols. In this full article, we report a comprehensively combined theoretical and experimental study on the mechanism of the insertion of gold carbenes into C–H and O–H bonds in phenol. It significantly revealed that the ligands have an important effect on C–H insertion and the reaction proceeds through a pathway involving the formation of an enolate-like intermediate. Moreover, two water molecules serving as a proton shuttle are believed to be the key issue for achieving chemoselective C–H functionalization, which is strongly supported by the DFT calculations and control experiments. It is the first time that a clear explanation is given about the prominent catalysis of gold carbenes toward C–H functionalization based on a theoretical and experimental study.

Correction for ‘Phosphine-catalyzed Friedel–Crafts reaction of naphthols with para-quinone methides: expedient access to triarylmethanes’ by Tao Zhou et al., Org. Biomol. Chem., 2017, DOI: 10.1039/c7ob00911a.