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Poplar is not only an important woody plant, but also a model species for molecular plant studies. We identified PagGRF11 (pAxG07Gg0005700), a homolog of the Arabidopsis AtGRF1 (AT4G37740) and AtGRF2 (AT2G22840) gene. We transformed the poplar clone “84K” with PagGRF11, and the transgenic overexpressed plants (PagGRF11-OE) showed plant height reduction (dwarfing), stem diameter increase, internode shortening, and larger leaf area. The Arabidopsis overexpression line grf-oe (Overexpression of PagGRF11 in Arabidopsis), mutant line atgrf (a loss-of-function mutant of the AtGRF1 gene of Arabidopsis thaliana), and mutant trans-complementary line atgrf+oe (overexpression of PagGRF11 in mutant plants (atgrf)) also showed different leaf size phenotypes. Further, tissue sections revealed that increased xylem production was the main cause of stem thickening. Transcriptome differential expression analysis of PagGRF11 overexpressed and control plants showed that PagGRF11 promoted CCCH39(C3H39) expression. The expression profile of CCCH39 in different tissues showed that it was highly expressed in xylem. Yeast single hybrid and instantaneous double luciferase assay results showed that PagGRF11 directly transcribed and activated CCCH39 expression through interaction with cis-acting element GARE (TCTGTTG), thus promoting xylem development. This is the first finding that GRF positively regulates xylem development through CCCH39 expression activation and further suggests that PagGRF11 is a potential target for increasing wood yield.

The possibility of developing new methods for the efficient construction of organic molecules via disconnections other than traditional functional group transformations has driven the interest in direct functionalization of C-H bonds. The ubiquity of C-H bonds makes such transformations attractive, but they also pose several challenges. The first is the reactivity and selectivity of C-H bonds. To achieve this, directing groups (DGs) are often installed that can enhance the effective concentration of the catalyst, leading to thermodynamically stable metallacyclic intermediates. However, the presence of a pendant directing group in the product is often undesirable and unnecessary. This may account for the limitation of applications of C-H functionalization reactions in more common and general uses. Thus, the development of removable or functionalizable directing groups is desirable. Another key problem is that the reactivity of the resulting M-C bond can be low, which may limit the scope of the coupling partners and hence limit the reaction patterns of C-H activation reactions. While the first Cp*Rh(III)-catalyzed C-H activation of arenes was reported only 7 years ago, significant progress has been made in this area in the past few years. We began our studies in this area in 2010, and we and others have demonstrated that diversified catalytic functionalization of arenes can be realized using Cp*Rh(III) complexes with high reactivity, stability, and functional group compatibility. This Account describes our efforts to solve some of these challenges using Rh(III) catalysis. We fulfilled our design and activation of the arene substrates by taking advantage of the nucleophilicity, electrophilicity, oxidizing potential, and properties of a participating ligand of the directing groups when the arenes are coupled with relatively reactive unsaturated partners such as alkenes and alkynes. These in situ funtionalizable roles of the DG allowed extensive chemical manipulation of the initial coupled product, especially in the construction of a diverse array of heterocycles. In the coupling of arenes with polar coupling partners, the polar Rh(III)-C(aryl) bond showed higher reactivity as both an organometallic reagent and a nucleophilic aryl source. The polar coupling partners were accordingly activated by virtue of umpolung, ring strain, and rearomatization. All of these transformations have been made possible by integration of the higher reactivity, stability, and compatibility of Rh(III)-C bonds into catalytic systems. We have demonstrated that to date some of these transformations can be achieved only under rhodium catalysis. In addition, by means of stoichiometric reactions, we have gained mechanistic insights into the interactions between the Rh-C bond and the other coupling partners, which have opened new avenues in future direct C-H functionalization reactions.

Reductive catalytic fractionation (RCF) has emerged as a new biorefinery paradigm for the fractionation and sequential utilization of entire components of biomass. Herein, we investigated the RCF of bamboo, a highly abundant herbaceous feedstock, in the presence of Pd/C catalyst. The lignin fraction in bamboo was preferentially depolymerized into well-defined low-molecular-weight phenols, with leaving carbohydrates pulp as a solid residue. In the soluble fraction, four major phenolic compounds, e.g., methyl coumarate/ferulate derived from hydroxycinnamic units and propanol guaiacol/syringol derived from β-O-4 units, were generated up to 41.7 wt% yield based on original lignin content. In the insoluble fraction, the carbohydrates of bamboo were recovered with high retentions of cellulose (68%) and hemicellulose (49%), which upon treatment with enzyme gave glucose (90%) and xylose (85%). Overall, the three major components of bamboo could efficient to be fractionated and converted into useful platform chemicals on the basis of this study.

The efficient and selective ortho-alkylation of N,N-dimethyl anilines via C–H addition to alkenes was achieved for the first time using a cationic half-sandwich yttrium catalyst. This protocol constitutes a straightforward and atom-economical route for the synthesis of a new family of tertiary aniline derivatives with branched alkyl substituents, which are otherwise difficult to obtain. DFT calculation studies suggest that the interaction between the yttrium atom and the NMe2 group plays an important role and the intramolecular C–H activation through a σ-bond metathesis pathway is the rate-determining step, which is consistent with the experimental KIE observations.

Depending on the reaction conditions, the oxidative Rh-catalyzed and Ag(I)-mediated process provides pyridine or sterically defined cyclopentanone scaffolds.

ConspectusThe possibility of developing new methods for the efficient construction of organic molecules via disconnections other than traditional functional group transformations has driven the interest in direct functionalization of C–H bonds. The ubiquity of C–H bonds makes such transformations attractive, but they also pose several challenges. The first is the reactivity and selectivity of C–H bonds. To achieve this, directing groups (DGs) are often installed that can enhance the effective concentration of the catalyst, leading to thermodynamically stable metallacyclic intermediates. However, the presence of a pendant directing group in the product is often undesirable and unnecessary. This may account for the limitation of applications of C–H functionalization reactions in more common and general uses. Thus, the development of removable or functionalizable directing groups is desirable. Another key problem is that the reactivity of the resulting M–C bond can be low, which may limit the scope of the co...

Depending on the reaction conditions, the oxidative Rh-catalyzed and Ag(I)-mediated process provides pyridine or sterically defined cyclopentanone scaffolds.

Rhodium(III)-catalyzed oxidative olefination of N-(1-naphthyl)sulfonamides has been achieved at the peri position. Three categories of olefins have been successfully applied. Activated olefins reacted to afford five-membered azacycles as a result of oxidative olefination-hydroamination. Unactivated olefins reacted to give the olefination product. 2-fold oxidative C-C and C-N coupling was achieved for allylbenzenes.

Treatment of nitrones of type (I) and (IV) with iodine results in selective formation of isoindolones.

Treatment of 4-functionalized pyridines with acetylenes in the presence of Cu(O-Ac)2 and Rh(III) catalyst allows an effective access to quinoline structures.

Internal redox cyclizations of nitrone-functionalized terminal alkynes (I) are mediated by simple iridium complexes to give the cyclized azomethine ylides (II), which undergo [3+2] dipolar cycloaddition reactions with several alkynes and alkenes.

Rh(III)-catalyzed oxidative coupling reactions between isoquinolones with 3-aryl groups and activated olefins have been achieved using anhydrous Cu(OAc)2 as an oxidant to give tetracyclic products. The nitrogen atom acts as a directing group to facilitate ortho C−H activation. This reaction can be one-pot starting from methyl benzohydroxamates, without the necessity of the isolation of isoquinolone products. A broad scope of substrates has been demonstrated, and both terminal and internal activated olefins can be applied. In the coupling of N-methylmaleimide, a Wacker-like mechanism was proposed, where backside attack of the NH group in isoquinolones is suggested as a key step. Selective C−H activation has also been achieved at the 8-position of 1-naphthol, leading to an olefination product.

In most cases, a selective diarylation takes place at the C-2 methyl group of the heterocyclic substrate.

A variety of pyridine-oxides undergoes a Pd-catalyzed oxidative coupling with substituted indoles at the 3-position.

Isolation of Azomethine Ylides and Their Complexes: Iridium(III)-Mediated Cyclization of Nitrone Substrates Containing Alkynes

Synthesis of γ-lactams via the oxidative coupling of benzamides with electron-poor olefins is demonstrated.

Catalytic oxidative coupling between acrylamides and alkynes was achieved using 0.5 mol % loading of [RhCp*Cl2]2 with Cu(OAc)2 as an oxidant. 2-Pyridones, iminoesters, and substituted indoles could be obtained as a result of the electronic and steric effects of the substituents in the acrylamides.

The aminopyridine substrates undergo oxidative coupling with alkynes and acrylates under conditions A) to generate N-pyridyl-substituted indoles or N-(2-pyridyl)-quinolones, respectively.

A methodology for the high yield and facile synthesis of isoquinolones from benzamides and alkynes via the oxidative ortho C−H activation of benzamides has been developed. Ag2CO3 proved to be an optimal oxidant when MeCN was used as a solvent, and [RhCp*Cl2]2 was utilized as an efficient catalyst. Both N-alkyl and N-aryl secondary benzamides can be applied as effective substrates. Furthermore, primary benzamides react with two alkyne units, leading to tricyclic products via double C−H activation and oxidative coupling. The reactivity of the structurally related 1-hydroxyisoquinoline was also demonstrated, where both N- and O-containing rhodacyclic intermediates can be generated, leading to the construction of different O- or N-containing heterocycles.

An efficient one‐pot four‐component coupling process for the synthesis of polyhydroquinoline derivatives catalyzed by montmorillonite K10 clay is described. This procedure has such advantages as short reaction time, high yields, and simple workup. The catalyst could be reused several times and keeps its initial activity in the recycle reactions.

Fe3+‐montmorillonite clay catalyst was used for the first time for pyrroles preparation by Paal–Knorr condensation. The features of this catalytic system are improved yields, mild conditions, a simple procedure, and high catalytic efficiency. The catalyst could be easily recycled and reused for three times without visible losing of activity.