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Major Diastereomer (major + diastereomer)
Selected AbstractsAsymmetric Cyclopropanation of Optically Active (1-Diethoxyphosphoryl)vinyl p -Tolyl Sulfoxide with Sulfur Ylides: A Rationale for DiastereoselectivityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2005Wanda H. Midura Abstract The title sulfoxide (S)-(+)- 1a was found to react with sulfur ylides affording the corresponding cyclopropanes in high yields. With fully deuterated dimethyl(oxo)sulfonium methylide, (CD3)2S(O)CD2, the cyclopropanation reaction occurred in a highly diastereoselective manner producing the cyclopropane 4a - d2 as a major diastereomer in which the newly formed quaternary ,-carbon atom is chiral due to isotopic substitution (CH2 vs. CD2). The diastereomer 4b - d2, having the opposite configuration at the ,-carbon atom, was obtained starting form the 2,2-dideuterio substituted vinyl sulfoxide, (S)-(+)- 1a - d2, and the nondeuterated ylide. The diastereomeric ratio in both reactions was found to be ca. 10:1. The reaction of (S)-(+)- 1a with diphenylsulfonium isopropylide yielded the cyclopropane (+)- 7 as a single diastereomer. X-ray structural studies of the crystalline 1-phosphorylvinyl sulfoxide 9 as well as density functional calculations (B3LYP/6-31G*) on (1-phosphoryl)vinyl sulfoxides revealed the origin of the experimentally observed diastereoselectivities and allowed us to propose a transition state model for the cyclopropanation reaction of chiral 1-phosphorylvinyl sulfoxides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Structures and properties of two diastereomeric cyclic sulfites derived from cis -3,4-di- tert -butylthiolane-3,4-diol and thionyl chlorideHETEROATOM CHEMISTRY, Issue 7 2003Sanae Tanaka cis-3,4-Di-tert-butylthiolane-3,4-diol (1) was treated with an equimolar amount of thionyl chloride in the presence of triethylamine or pyridine in several solvents of different polarity to furnish two diastereomeric sulfites 2a and 2b generally in excellent combined yields. Although 2a was consistently formed as the major diastereomer when pyridine was used as the base, 2a and 2b were formed in approximately equal amounts when triethylamine was used as the base in polar solvents. X-ray crystallographic analyses revealed that the SO group of 2a is anti to the thiolane ring and that of 2b syn to the thiolane ring. Density functional theory calculations (B3LYP/6-31G* level) revealed that 2a is less stable than 2b by 1.28 kcal mol,1, although 2a was formed generally as the predominant diastereomer. Spectroscopic data of 2a and 2b are discussed with emphasis on comparison with those obtained by calculations. Treatment of 2a and 2b with m-chloroperbenzoic acid resulted in the oxidation of the divalent sulfur atom of the thiolane ring and not the sulfite sulfur atom. The above oxidations took place exclusively at the syn-side with respect to the tert-butyl groups.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:587,595, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10192 [source] gem -Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Michael G. Edwards The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem -dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C23H26O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry. [source] 1-(,-Aminobenzyl)-2-naphthol: A New Chiral Auxiliary for the Synthesis of Enantiopure ,-Aminophosphonic AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2009Kirill Abstract Ooh Betti! A new diastereoselective synthesis of ,-aminophosphonates has been developed based on the reaction of trialkyl phosphites with chiral imines derived from (R)- or (S)-1-(,-aminobenzyl)-2-naphthol (Betti base; see scheme, X=H, CH3, or Br). The reaction proceeds with high diastereoselectivity. Treatment with HCl results in the formation of the desired ,-aminophosphonic acids. A new diastereoselective synthesis of ,-aminophosphonates has been developed, based on the reaction, in the presence of trifluoroacetic acid, of trialkyl phosphites with chiral imines derived from (R)- or (S)-1-(,-aminobenzyl)-2-naphthol. The reaction proceeds at room temperature in toluene with high diastereoselectivity. The major diastereomer can be separated by crystallization from an appropriate solvent. The relative configuration of both chiral centers of the major diastereomer was determined by single-crystal X-ray structure analysis. The desired ,-aminophosphonic acids can be obtained in enantiopure form by treatment of the corresponding diastereomers with HCl. [source] | ||||||||||