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Quaternary Carbon Centers (quaternary + carbon_center)
Selected AbstractsFormation of a Quaternary Carbon Center Through the Pd(0)/PhCOOH-Catalyzed Allylation of Cyclic ,-Keto Esters and 1,3-Diketones with Alkynes.CHEMINFORM, Issue 4 2005Nitin T. Patil Abstract For Abstract see ChemInform Abstract in Full Text. [source] Germanium(II)-Mediated Reductive Cross-Aldol Reaction of Aldehydes: Synthesis of Aldols with Diastereocontrolled Quaternary Carbon Centers.CHEMINFORM, Issue 44 2007Shin-ya Tanaka Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Construction of Chiral Quaternary Carbon Centers by Pd-Catalyzed Asymmetric Allylic Substitution with P,N-1,1,-Ferrocene Ligands.CHEMINFORM, Issue 12 2005Xue-Long Hou Abstract For Abstract see ChemInform Abstract in Full Text. [source] Asymmetric Total Synthesis of Fredericamycin A: An Intramolecular Cycloaddition PathwayCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Shuji Akai Dr. Abstract The asymmetric total synthesis of the potent antitumor antibiotic fredericamycin A ((S)- 1) was achieved by the intramolecular [4+2] cycloaddition of the silylene-protected styrene derivative (S)- 7 followed by the aromatic Pummerer-type reaction of the sulfoxide (S)- 5. Although we had already succeeded in the total synthesis of racemic 1 by the same approach, synthesis of its asymmetric version was more complicated than we had expected due to the difficulties involved in constructing the quaternary carbon center and the tendency of this center to undergo facile racemization. Racemization of this center during the installation of the acetylene moiety on the dione (R)- 8 was the most serious aspect. Systematic studies of its DE-ring analogue (R)- 25 revealed that racemization of the quaternary carbon center proceeded by a retro-aldol,aldol reaction of the initial adduct, (1R)- 39,a -Li, and that the degree of racemization was dependent on the reaction temperature. The racemization process could be completely depressed by keeping the reaction temperature at ,78,°C. The construction of the stereogenic quaternary carbon center was achieved by the lipase-catalyzed desymmetrization of the prochiral 1,3-diol 9,a bearing the DEF-ring moiety. These studies enabled us to attain the asymmetric total synthesis of (S)- 1 while completely retaining the chiral integrity created by the enzymatic reactions. [source] | ||||||||||