Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo compounds or N-tosylhydrazones show that these transformations also work with other transition metals, demonstrating the generality of the diazo compounds as new cross-coupling partners in transition-metal-catalyzed coupling reactions.

Surveys were carried out to better understand the tick vector ecology and genetic diversity of Huaiyangshan virus (HYSV) in both regions of endemicity and regions of nonendemicity. Haemaphysalis longicornis ticks were dominant in regions of endemicity, while Rhipicephalus microplus is more abundant in regions of nonendemicity. HYSV RNA was found in human and both tick species, with greater prevalence in H. longicornis and lesser prevalence in R. microplus. Phylogenetic analyses indicate that HYSV is a novel species of the genus Phlebovirus. Recently, a hemorrhagic fever-like disease caused by a novel bunyavirus occurred in China (14, 16). Yu et al. reported the disease as severe fever with thrombocytopenia syndrome (SFTS) (14). As thrombocytopenia is not specific for this disease and is present in nearly all hemorrhagic fevers caused by viruses (11) or Rickettsia (15), we previously proposed naming the syndrome Huaiyangshan hemorrhagic fever (HYSHF) and the virus Huaiyangshan virus (HYSV) (16). Haemaphysalis longicornis ticks might be the vector of HYSV (14, 16). However, less is known about the arthropod vector ecology, the genetic diversity, and the phylogeny of HYSV. Thus, we performed an investigation in regions of endemicity and nonendemicity in Henan and Hubei provinces ( Fig. 1).A total of 17,731 adult ticks were collected (Table 1). After morphological examination and sequence analysis of mitochondrial 12S ribosomal DNA (rDNA) as described previously (2, 16), only H. longicornis and Rhipicephalus microplus were found. In the regions of endemicity, 4,501 ticks (3,498 H. longicornis and 1,003 R. microplus) were collected from 15 counties of Henan and Hubei. In the regions of nonendemicity, 13,230 ticks (400 H. longicornis and 12,830 R. microplus) were collected from 23 counties of Hubei. These data suggested that H. longicornis and R. microplus were the dominant species in regions of endemicity and regions of nonendemicity, respectively.All ticks were grouped into 1,180 pools (450 pools from a region of endemicity and 730 pools from a region of nonendemicity) according to species, host, and geographic origin. H. longicornis and R. microplus represented 365 (30.93%) and 815 (69.07%) pools, respectively. For screening HYSV and sequencing the partial S segment (nucleotides [nt] 63 to 663) or L segment (nt 2208 to 3121) and whole-genome sequences of HYSV, total RNA was extracted from ticks and human sera and was then subjected to reverse transcription-PCR (RT-PCR) as described previously (16). As a result, HYSV RNA was identified in 18 (4.93%) H. longicornis pools and in 5 (0.613%) R. microplus pools, suggesting that both species can carry HYSV. Remarkably, the HYSV RNA-positive H. longicornis ticks were found only in the regions of endemicity, whereas HYSV RNA was identified in R. microplus ticks from both the regions of endemicity (2 pools) and neighboring regions of nonendemicity (3 pools) (Fig. 1). Obviously, the prevalence of HYSV was higher in H. longicornis ticks than in R. microplus ticks and higher in...

Golden bromination: A highly efficient and mild AuCl3‐catalyzed bromination of aromatic rings with N‐bromosuccinimide (NBS) has been developed. This method works with a low catalyst loading (down to 0.01 mol %) and can be combined with transition metal catalyzed transformations to deliver various aryl products.

Transition-metal-catalyzed cross-coupling reactions involving a carbene migratory insertion process have been developed rapidly during the past ten years. Such a type of coupling reactions provides useful methodologies for the construction of carbon−carbon and carbon−heteroatom bonds. On the basis of the carbene migratory insertion process, catalytic cascade reactions have also been designed and developed, affording versatile methods for the construction of complex molecules. In this review, four types of transition-metal-catalyzed cascade reactions involving the carbene migratory insertion process are discussed.

Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, β-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol).

An efficient rhodium(III)-catalyzed synthesis of 2H-chromene from N-phenoxyacetamides and cyclopropenes has been developed. The reaction represents the first example of using cyclopropenes as a three-carbon unit in rhodium(III)-catalyzed C(sp(2))-H activations.

Ahead of the PAC: Polycyclic aromatic compounds (PACs) can be easily accessed by the combination of Suzuki–Miyaura cross‐coupling and a [Rh2(OAc)4]‐catalyzed carbene reaction using easily available bis(N‐tosylhydrazone)s as intermediates (see scheme; Ts=4‐toluenesulfonyl).

The Pd(OAc)(2)-catalyzed reaction between alpha-diazocarbonyl compounds and allyl bromides or chlorides leads to the formation of 1,3-diene derivatives.