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Stereodivergent Synthesis (stereodivergent + synthesis)
Selected AbstractsStereodivergent Syntheses of Highly Substituted Enantiopure 4-Alkoxy-3,6-dihydro-2H -1,2-oxazines by Addition of Lithiated Alkoxyallenes to Carbohydrate-Derived AldonitronesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Matthias Helms Abstract Additions of lithiated alkoxyallenes to D -glyceraldehyde-based nitrones 1 and 2 did not provide the expected hydroxylamine derivatives. Instead, a novel [3+3] cyclization process furnished 4-alkoxy-3,6-dihydro-2H -1,2-oxazines 9,14 with excellent syn selectivities and in moderate to good yields. Through precomplexation of the nitrones the corresponding anti -configured 1,2-oxazines 9, 10 and 13 could be obtained with high stereoselectivity. The reactions of nitrones 3,6, derived from D -erythrose or D -threose, generally proceeded less diastereoselectively, but reasonable yields of anti -configured 1,2-oxazines such as anti - 17 and anti - 19 could be obtained under Lewis acid promotion conditions. This was also the case for reactions of the D -arabinose-derived nitrone 7, which provided the anti -1,2-oxazines 23 and 24 with excellent diastereoselectivity and in good yields. Bis-nitrone 8 and lithiated methoxyallene furnished a mixture of six compounds, among which the major componentwas the C2 -symmetric syn/syn -1,2-oxazine 29. The diastereoselectivities of these reactions are interpreted on the basis of Dondoni's model for reactions between organolithium compounds and nitrones. The mechanisms for formation of 1,2-oxazines and of side products are discussed. The method introduced here seems to be of broad applicability and an excellent tool for diastereoselective chain elongation of carbohydrate derivatives, affording stereodefined precursors of aminopolyols and other highly functionalized compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A Temporary Stereocentre Approach for the Stereodivergent Synthesis of Either Enantiomer of ,-MethyloctanalEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2007D. Gangani Niyadurupola Abstract The aldol reaction of a chiral N -(acyl)oxazolidin-2-one with 2-methyleneoctanal or (E)-2-methyloct-2-enal affords chiral aldol products whose alkene functionalities were hydrogenated using Brown's or Wilkinson's catalyst to afford syn - or anti -selective products with excellent levels of diastereocontrol. Subsequent retro -aldol cleavage of these syn - or anti -adducts resulted in the formation of either (R)- or (S)-enantiomer of ,-methyloctanal with no racemisation occurring, which could be derivatised in-situ to afford chiral dithiane, alcohol or ,,,-unsaturated ester products in enantiopure form.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] ChemInform Abstract: Stereodivergent Synthesis of Fused Bicyclopyrazolidines: Access to Pyrazolines and Pyrrolidines.CHEMINFORM, Issue 8 2010Terry P. Lebold Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Stereodivergent Synthesis of ,-Hydroxy-,-methylene Lactones via Vinyl Epoxides.CHEMINFORM, Issue 43 2008Marion Davoust 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 of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Stereodivergent Synthesis of Chiral 2-Alkenylaziridines: Palladium(0)-Catalyzed 2,3-cis-Selective Aziridination and Base-Mediated 2,3-trans-Selective Aziridination.CHEMINFORM, Issue 30 2004Hiroaki Ohno Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereodivergent Synthesis of 5a-Carba-hexopyranoses from Carbohydrates via 6-exo-dig Radical Cyclization: Preparation of 5a-Carba-,-D-manno-, ,-D-allo-, ,-L-talo- and ,-L-Gulopyranose Pentaacetates from D-Mannose.CHEMINFORM, Issue 7 2004Ana M. Gomez Abstract For Abstract see ChemInform Abstract in Full Text. [source] Study of the Reactions Between Vinylmagnesium Bromide and Imines Derived from (R)-Glyceraldehyde , The Key Step in the Stereodivergent Synthesis of Conveniently Protected, Enantiopure syn- and anti-2-Amino-1,3,4-butanetriol Derivatives.CHEMINFORM, Issue 39 2003Ramon Badorrey No abstract is available for this article. [source] A Stereodivergent Synthesis of All Stereoisomers of Centrolobine: Control of Selectivity by a Protecting-Group ManipulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 44 2009Bernd Schmidt Prof. Abstract All stereoisomers of the natural product centrolobine are selectively synthesized, by starting from a common precursor. Key steps are an enantioselective allylation with enantiomerically pure allylsilanes, a tandem ring-closing metathesis,isomerization reaction, and a Heck reaction by using an arene diazonium salt. By choosing appropriate conditions for the final deprotection step, either the cis -configured centrolobines or their epimers are selectively obtained. [source] Highly Selective Stereodivergent Synthesis of Separable Amide Rotamers, by Using Pd Chemistry, and Their Thermodynamic BehaviorCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2009Nobutaka Ototake Abstract Going separate ways: By using ,-allyl,palladium chemistry (path,A) and PdII -catalyzed Claisen chemistry (path,B), a highly selective stereodivergent synthesis of separable amide rotamers was achieved (see scheme). By using Pd chemistry, a highly selective stereodivergent synthesis of separable amide rotamers was achieved. Allylation of 2,4,6-tri- tert -butylanilides using a ,-allyl,Pd catalyst gave N-allylated anilides with moderate-to-excellent Z -rotamer selectivity (Z/E=3 to >50). The Z -rotamer selectivity depends considerably on the substituent on the anilide substrates. On the other hand, the E rotamers of N-allylated 2,4,6-tri- tert -butylanilides were obtained with almost complete selectivity (E/Z>50) through O-allylation of 2,4,6-tri- tert -butylanilides and the subsequent PdII -catalyzed Claisen rearrangement of the resulting O-allyl imidate. The prepared anilide rotamers changed to equilibrium mixtures in which the E rotamer was the major isomer when heated in toluene. [source] | ||||||||||