The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m−2 s−1). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3–37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons−1 and a maintenance requirement of 0.0133 and 0.0068 mol photons g−1 h−1 were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3–37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.

The completely OH-selective Prins cyclization has been realized from the enantioselective ene reaction product. A variety of 4-hydroxyl-tetrahydropyrans were exclusively generated via FeCl(3)-catalyzed Prins reaction. Excellent stereoselectivities (up to >99:1 dr and >99.5:0.5 er) were obtained for a remarkably broad range of substrates under mild reaction conditions. The control experiments, including NOE effects and (18)O-labeling studies, as well as DFT calculations were conducted to provide fundamental insights into the mechanism of the reaction. A different [2 + 2] cycloaddition process was suggested to rationalize the observed OH-selectivity.

Previous studies have reported high serum concentrations of polybrominated diphenyl ethers, especially decabromodiphenyl ether (BDE-209), in the residents of an electronic waste (e-waste) dismantling site in Guiyu town, South China. In the present study, human serum samples in this region were collected and pooled for the identification of hydroxylated diphenyl ethers (OH-PBDEs). Three OH-PBDEs, including two hydroxylated octabromodiphenyl ethers (OH-octaBDEs, 6-OH-BDE196 and 6-OH-BDE199) and one hydroxylated nonabromodiphenyl ether (OH-nonaBDE, 6'-OH-BDE206), were first structurally identified. Identification was done by coeluting a mixture of synthetic authentic standards with the methylated OH-PBDEs from the pooled samples using two gas chromatography columns with different polarities. The results were supported by full scan mass spectrometric data in electron capture negative ionization mode. All three OH-PBDE metabolites had hydroxy groups substituted in the ortho position. These results indicate that hydroxylated higher brominated diphenyl ethers such as OH-octaBDEs and OH-nonaBDEs can accumulate in human blood. The results suggest that higher brominated diphenyl ethers could be oxidatively metabolized into OH-PBDEs in humans. Because low brominated OH-PBDEs can also be detected in abiotic media, further investigations are needed to determine the presence of higher brominated OH-PBDEs in the environment in this region.

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Bifunctional N,N'-dioxide catalysts have been developed for highly enantioselective cyanosilylation of alpha,alpha-dialkoxy ketones. This process, catalyzed by in-situ-prepared proline-derived N,N'-dioxide 2b, produced the corresponding cyanohydrin trimethylsilyl ethers in excellent yields (up to 99%) with high enantioselectivities (up to 93% ee). A reasonable mechanism was proposed according to the observation of the linear effect, 1H NMR spectra, isolated cyanohydrin, and the roles of the NH and N-oxide moieties of the catalyst.

Key message Introgressing one-eighth of synthetic hexaploid wheat genome through a double top-cross plus a twophase selection is an effective strategy to develop high-yielding wheat varieties. Abstract The continued expansion of the world population and the likely onset of climate change combine to form a major crop breeding challenge. Genetic advances in most crop species to date have largely relied on recombination and reassortment within a relatively narrow gene pool. Here, we demonstrate an efficient wheat breeding strategy for improving yield potentials by introgression of multiple genomic regions of de novo synthesized wheat. The method relies on an initial double top-cross (DTC), in which one parent is synthetic hexaploid wheat (SHW), followed by a two-phase selection procedure. A genotypic analysis of three varieties (Shumai 580, Shumai 969 and Shumai 830) released from this program showed that each harbors a unique set of genomic regions inherited from the SHW parent. The first two varieties were generated from very small populations, whereas the third used a more conventional scale of selection since one of bread wheat parents was a pre-breeding material. The three varieties had remarkably enhanced yield potential compared to those developed by conventional breeding. A widely accepted consensus among crop breeders holds that introducing unadapted germplasm, such as landraces, as parents into a breeding program is a risky proposition, since the size of the breeding population required to overcome linkage drag becomes too daunting. However, the success of the proposed DTC strategy has demonstrated that novel variation harbored by SHWs can be accessed in a straightforward, effective manner. The strategy is in principle generalizable to any allopolyploid crop species where the identity of the progenitor species is known.

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