摘要:

AbstractVarious problems arising in experimental organic chemistry can be clarified by molecular mechanics or force field calculations: molecular dynamics (conformational analysis and internal rotation), the search for the most stable isomer of various polycyclic hydrocarbons, reactivity calculations, including solvolysis of bridgehead substituted systems. Such calculations are shown to be useful in elucidating the mechanism of multistep carbonium ion rearrangement, for predicting the structure and stability of anti‐Bredt olefins, and also offer an explanation for the selectivity observed in the hydrogenolysis of strained polycyclic smallring hydrocarbons, for the identification of long bonds and electronic effects, for the analysis of late transition states, and for the product distribution in complex reaction

ISSN:0570-0833    

DOI:10.1002/anie.198300013

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractChemistry and biology paved the way for a new scientific discipline, molecular genetics. The breathtaking progress in deciphering the genetic machinery of a living being within the last 20 years may be attributed mainly to the experimental skill and ingenuity of molecular biologists. Chemists lost interest in the investigation of biological problems. The advances in genetic engineering exemplify the new demands chemists are confronted with in contemporary science. Following a short introduction on the genetics of bacteria, the articles deals with the molecular basis of gene cloning, which is subdivided intoin vitrorecombination of nucleic acids andin vivotransformation of cells. Next, the criteria for the selection of passenger DNA, vectors, and host cells are discussed. Recombination and transformation are easy‐to‐learn experimental techniques, whereas the search for the positive clone requires detailed knowledge of microbiology and the ability to handle of a battery of modern biochemical techniques. Finally, the automated chemical synthesis of gene fragments serves to demonstrate that chemistry is starting to make its comeback into molecular biol

ISSN:0570-0833    

DOI:10.1002/anie.198300131

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe addition of carbanionic organometallic compounds (usually RLi or RMgX) to a carbonyl group—a key step in numerous syntheses—is not always straightforward. Depending on the substrate, various complications and problems may arise, but in many cases these can be remedied by addition of (RO)3TiCl, (RO)3ZrCl or (R2N)3TiX to the classic lithium and Grignard reagents. This usually leads to formation of stable organo‐titanium and ‐zirconium compounds which react highly selectively with carbonyl groups. For example, CH3Ti(OiPr)3reacts five orders of magnitude faster with benzaldehyde than with acetophenone at room temperature; reagents of the type RTi(OiPr)3add smoothly to nitro‐, ido‐, or cyano‐subsituted benzaldehyde, and the reactions may be performed in chlorinated solvents or acetonitrile; the zirconium analogues have particularly low basicity and add in high yield to α‐ and β‐tetralones or to substrates containing a nitroaldol group; the inclusion of chiral OR*groups gives enantioselective reagents (up to 90%ee); allylic (RO3)Ti‐ derivatives react only at the more highly substituted carbon atom and, in addition, react diastereoselectively (up to 98%ds) with unsymmetrical ketones. Finally, titanium reagents have also been found to effect novel transformations such as direct geminal dialkylation (CO→CMe2) and alkylative amination [CO→CR(NR 2′)]. The modification and finetuning (“taming”) of carbonyl reactivity obtainable by use of the new reagents is not dearly bought; starting materials are the cheap and harmless “titanates”, “zirco

ISSN:0570-0833    

DOI:10.1002/anie.198300311

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198300451

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198300461

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 1. DOI:10.1002/anie.198300010

ISSN:0570-0833    

DOI:10.1002/anie.198300471

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198300481

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 57. DOI:10.1002/anie.198300570

ISSN:0570-0833    

DOI:10.1002/anie.198300492

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198300501

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198300511

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY