Stereoselektive Synthese von β‐Aminoalkoholen aus optisch aktiven α‐Aminosäuren

Abstract

verbruckend angelagert. Die As-I-Abstande zu den p3bzw. k-verbruckenden I-Atomen II und 12 liegen zwischen 306.8 und 334.9 pm. Dariiber hinaus weisen alle As-Atome jeweils drei kurze As-I-Bindungen im Bereich zwischen 257.8 und 273.6 pm auf. Das vor kurzem charakterisierte Anion hat eine vollig andere S t r~k t u r l~~l : An eine zentrale [As4CI ,,J4--Einheit mit cubanartiger Struktur sind vier AsC1,-Molekule sehr locker angelagert.Das gemeinsame Bauprinzip bei [As,I,,]~-und [Sb,I& laBt erwarten, da13 noch andere, ahnlich aufgebaute Iodoarsenat(r~r)-und -antimonat(r~~)-Ionen durch Variation des Kations zu erhalten sind.

Vanadium‐Catalyzed Asymmetric Oxidation of Sulfides Using Schiff Base Ligands Derived from β‐Amino Alcohols with Two Stereogenic Centers

“…With the expectation that the enantioselectivity might be substantially influenced by structural changes in the ligands, we prepared Schiff base ligand 2 and ligands 3a-i (Scheme 1) according to a literature method for evaluation. [25,26] Ligand 2, derived from a β-amino alcohol with one stereogenic center, afforded poor enantioselectivity (3 % ee). In contrast, ligand 3a, derived from a β-amino alcohol with two stereogenic centers, gave the desired product with enhanced enantioselectivity (61 % ee) at room temperature.…”

“…[8] We wish to investigate the structural influence of the β-amino alcohol moiety, especially those with two stereogenic centers, to find a highly efficient catalyst system for this reaction. Because phenylalanine is a very cheap, commercially available material that can be modified to different target products with routine procedures, [25,26] we chose it as the starting material for the screening of the amino alcohols with two stereogenic centers for the enantioselective oxidation of sulfides.…”

New Approaches to the Use of Amino Acids as Chiral Building Blocks in Organic Synthesis [New Synthetic Methods (85)]

“…[19] In contrast, TiC1,-mediated ene reactions on the same aldehydes lead to high degrees of chelation control. [341 MgBr,-mediated addition of Me,SiCN to the aldehydes 18 proceeds with modest chelation control (ds z 80 TiCb 86 19 20 The explanation for these nonuniform findings may be based on steric inhibition of chelation.…”

“…16] The lack of stereoselective methods is unfortunate, because /3-amino alcohols constitute a pharmaceutically and biologically interesting class of substances. The compounds themselves frequently display appreciable biological activity, as in the case of the antibiotic chloramphenicol (ll);['] in other cases these structures are found as components of more complex active substances or natural products-for example, in the coronary agent alifedrin (12)!8] the aminopeptidase-B inhibitor bestatin (13), 19] the blood-pressure-reducing renin inhibitor pepstatin (14) and its synthetic analogues,['01 amino sugars [e.g., tolyposamine ( The first part of this progress report describes methods by which a-amino aldehydes (and a-amino ketones) can be converted selectively into either of the two diastereomeric forms of /3-amino alcohols. Attention will be given not only to Grignard and aldol additions, but also to cyanohydrin-and epoxide-forming reactions of Me,SiCN and sulfur ylides, respectively, as well as to hetero-Diels-Alder reactions.…”

Stereoselective Transformations with Configurationally Labile α‐Phenylselenoalkyllithium Compounds

“…74.8,125.8,127.4,10 (48.4 mg,0,15 mmol) with 64% ee and triphenyltin hydride (201 mg, 0.57 mmol) led to ent-20 (16.4mg, 62%) as a colorless liquid. (17,18) : The reaction between organolithium compound 8 and aldehyde 16 [23] was carried out as described for 9 and 10 (inverse addition mode). The reaction products were separated by MPLC with ether (5 %) in petroleum ether to furnish the diastereomeric adducts 17 and 18.…”