67074-38-8Relevant academic research and scientific papers
Stereospecific Construction of Contiguous Quaternary All-Carbon Centers by Oxidative Ring Contraction
Yu, Xin,Hu, Jiadong,Shen, Zhigao,Zhang, Hui,Gao, Jin-Ming,Xie, Weiqing
supporting information, p. 350 - 353 (2016/12/30)
Oxidative ring contraction of cyclic α-formyl ketones was facilitated by the action of H2O2under operationally simple and environmentally benign reaction conditions. The process was highly regioselective and enables stereospecific construction of contiguous quaternary all-carbon centers from stereodefined all-substituted all-cyclic ketones. The asymmetric syntheses of (+)-cuparene and (+)-tochuinyl acetate were also successively achieved by taking advantage of this novel protocol.
Stereoselective synthesis of quaternary benzylic carbons using C2 symmetric imidazolines and tetrahydrofuran as electrophile
Dalko, Peter I.,Langlois, Yves
, p. 8107 - 8117 (2007/10/03)
Alkylative ring opening of tetrahydrofuran in the presence of 9-BBN triflate is studied. Dianions derived from C2 symmetric imidazolines induce excellent to modest acyclic diastereoselectivity to form quaternary benzylic centers, using the 9-BBN triflate/THF system or methyl iodide as electrophiles. The direction of the stereoinduction is consistent in both cases. Absolute configuration for the newly created stereogenic center was established by chemical correlation. Low-temperature NMR studies of the dilithiated intermediates 42 and 43 suggest the presence of N- and C- metalated compounds, where the metal-bearing benzylic carbon is sp3 hybridized.
Enantioselective Synthesis of Polyfunctional Small Building Blocks with a Quaternary Stereogenic Center
Enders, Dieter,Zamponi, Andreas,Schaefer, Thomas,Nuebling, Christoph,Eichenauer, Herbert,et al.
, p. 1707 - 1722 (2007/10/02)
Application of the SAMP-/RAMP-hydrazone method offers an efficient and flexible access to compounds with a quaternary stereogenic center.Examples bearning silyl, thio, phenyl, aldo, keto, ester, and alkyl functionalities are described.The 2-phenylaldehydes and -ketones and the β-keto esters 4 were obtained in good overall yields and with variable enantiomeric excesses.The synthesis of the thiolated 2-formyl and 3-formyl carboxylic esters 12 was achieved in high overall yields and with high enantiomeric excesses.The silylated carboxylic ester and acids 16 were produced in moderate to high overall yields and with moderate to excellent enantiomeric excesses, depending on the electrophile used for the quaternization.The absolute configurations of the compounds 12 and 16 were determined by X-ray structure analyses, and the mechanism of the quaternization is postulated. - Key Words: Asymmetric synthesis / SAMP,RAMP-Hydrazones
Intramolecular Nucleophilic Addition to Unsaturated Carbon. Dependence of Cyclization Efficiency on the Method of Carbon-Carbon Bond Cleavage Utilized To Generate the Reactive Species
Paquette, Leo A.,Gilday, John P.,Maynard, George D.
, p. 5044 - 5053 (2007/10/02)
The following three reactions have been studied for the purpose of comparing their intrinsic ability to generate carbanionic intermediates capable of intramolecular cyclization: (a) the Haller-Bauer cleavage of ketones 15a and 15b, as well as the (S)-(+)-antipode of 15a (viz. 47); (b) the base-promoted cleavage of 1,1-diarylcarbinols 16a and 16b; (c) decarboxylative elimination within the methyllithium adducts of carboxylic acids 17a and 17b.The Haller-Bauer process proceeds predominantly via carbanion intermediates, which most often experience protonation to give 18 an d 21.Cyclization becomes possible, however, under certain circumstances and reaches a maximum of 33percent with NaNH2 in benzene.Using (+)-47 as a probe, it has been possible to ascertain that 56percent of the reactive intermediate molecules racemize and that only the racemic species generates cyclic product.On the other hand, the Cram-type cleavages of 16a and 16b proceed mainly by homolytic cleavage to generate the benzophenone radical anion and free-radical intermediate.The latter dimerize, capture solvent, and abstract hydrogen to varying degrees depending upon counterion and solvent.Finally, reactions of type c are the most efficient at effecting intramolecular ring closure.
