Metal-Free Enantioselective 1,4-Addition of Diarylphosphine Oxides to α,ß-Unsaturated Carboxylic Esters.

The catalytic asymmetric conjugate addition of phosphorus nucleophiles to unsaturated compounds, catalyzed by metallic or nonmetallic catalysts, has been extensively developed. However, the enantioselective transformations involving α,ß-unsaturated carboxylic esters for constructing chiral c-p bonds have been rarely reported, particularly in metal-free processes. In this study, we present a novel metal-free methodology for enantioselective 1,4-addition of diarylphosphine oxides to α,ß-unsaturated carboxylic esters using classical chiral oxazaborolidine catalysts. Remarkably high yields and enantioselectivities were obtained for most of the products. Furthermore, these valuable chiral phosphorus esters serve as crucial intermediates that can be transformed into various derivatives including amides, acids, and alcohols in a single step.

Tetrabutylammonium Bromide-Catalyzed Transfer Hydrogenation of Quinoxaline with HBpin as a Hydrogen Source.

A metal-free environmentally benign, simple, and efficient transfer hydrogenation process of quinoxaline has been developed using the HBpin reagent as a hydrogen source. This reaction is compatible with a variety of quinoxalines offering the desired tetrahydroquinoxalines in moderate-to-excellent yields with Bu4NBr as a noncorrosive and low-cost catalyst.

Hydrogenation of Alkynes and Olefins Catalyzed by Quaternary Ammonium Salts.

Catalytic hydrogenation of unsaturated hydrocarbons to alkenes and alkanes using molecular hydrogen is one of the most fundamental transformations in organic synthesis. While methodologies involving transition metals as catalysts in homogeneous and heterogeneous processes have been well developed, metal-free catalytic hydrogenation offers an ideal approach for future chemistry. Herein, the common and inexpensive quaternary ammonium salts are first introduced as catalysts in the catalytic hydrogenation system for the transformations from alkynes or olefins into the corresponding olefins or alkanes. Interestingly, the hydrogenation process of alkynes can be controlled to selectively produce alkenes or alkanes under different conditions. Moreover, the possible mechanism is discussed in new insights into the catalytic behavior of quaternary ammonium salts.

[Difference and variation of the sef14 operon gene clusters in S. enteritidis and closed serogroup-D Salmonella].

OBJECTIVE: In order to reveal why SEF14 fimbriae are restrictively expressed on strains of serogroup D salmonella, mainly S. enteritidis and S. dublin, the difference and variation of the sef14 operon gene clusters in S. enteritidis and related serogroup-D Salmonella were analyzed. METHODS: The genes encoding subunits of sefA, sefD and sefR in S. pullorum, S. enteritidis and S. dublin were amplified by PCR method and then sequenced to analyze the the difference and variation, respectively. RESULTS: The results of PCR amplification showed that prevalence of sefA, sefD and sefR genes in S. enteritidis and S. dublin was 100%. In 18 isolates of S. pullorum, the prevalence of sefA gene was 100%,while the prevalence of sefD and sefR genes was 38.9% (7/18), and 11 strains isolated after 1980s did not contain any gene sefDor sefR. The sequencing data of PCR products revealed that sequences of sefA, sefD and sefR genes in S. enteritidis and S. dublin were identical with those those from NCBI GenBank data which accession number were L11008, U07129 and AF233854, respectively. Interestingly, among the 7 strains of S. pullorum before 1980s, the sefD sequence has a missing base pair at position 196 and caused open reading frame (ORF) shift, resulting in a stop codon (TAG) at position 71 amino acid residual (Leu of TTA at position 214 - 216 shift into stop codon of TAG at position 215 - 217). Unlike S. pullorum, all S. enteritidis and S. dublin tested could express SEF14 fimbriae in vitro. CONCLUSION: Based on the data of the difference and variation of sef14 operon gene clusters between S. enteritidis and S. pullorum, we may explain why SEF14 fimbriae in S. pullorum could not be expressed.