Synthese von ‘D-Isothreonin’ und ‘L-Alloisothreonin’ aus L-Alanin

Synthesis of ‘D -Isothreonine’ and ‘L -Alloisothreonine’ Starting from L -Alanine Starting from L -alanine, ‘D -isothreonine’ ( = (2R, 3S)-3-amino-2-hydroxybutanoic acid) and ‘L -alloisothreonine’ ( = (2S, 3S)-3-amino-2-hydroxybutanoic acid) were synthesized.     

Herstellung und Solvolyse von 3-substituierten p-Toluolsulfonsäure-(1-adamantyl)estern

The Preparation and Solvolysis of 3-substituted 1-Adamantyl Toluenesulfonates Methods for the preparation of some hitherto unknown 3-iubstitutetl 1-adamantyl toluenesulfonates are evaluated. Their solvolysis products in dioxane/water 70:30 are reported.     

Herstellung enantiomerenreiner Derivate von 3-Amino- und 3-Mercaptobuttersäure durch SN2-Ringöffnung des β-Lactons und eines 1,3-Dixoanons aus der 3-Hydroxybuttersä ure

Preparation of Enantiomerically Pure Derivatives of 3-Amino- and 3-Mercaptobutanoic Acid by S_N2 Ring Opening of the β-Lactone and a 1,3-Dioxanone Derived from 3-Hydroxybutanoic Acid From (S)-4-methyloxetan-2-one ( 1 ), the β-butyrolactone readily available from the biopolymer ( R )-polyhydroxybutyrate (PHB) and various C, N, O and S nucleophiles, the following compounds are prepared:(s)-2-hydroxy-4-octanone ( 3 ), (R)-3-aminobutanoic acid ( 7 ) and its N-benzyl derivative 5 , (R)-3-azidobutanoic acid ( 6 ) (R)-3-mercaptobutanoic acid ( 10 ), (R)-3-(phenylthio)butanoic acid ( 8 ) and its sulfoxide 9 . The (6R)-2,6-dimethyl-2-ethoxy-1,3-dioxan-4-one ( 4 ) from (R)-3-hydroxybutanoic acid undergoes S^N2 ring opening with benzylamine to give the N-benzyl derivative (ent- 5 ) of (S)-3-aminobutanoic acid in 30?40% yield.     

Synthese von triafulvalen-vorstufen durch ‘carben-dimerisierung’ von 1-halogeno-1-lithiocyclopropanen

Synthesis of Triafulvalene Precursors by ‘Carbene-Dimerization’ of 1-Halogeno-1-lithiocyclopropanes Bi(cyclopropylidenes) 7a , 7c , and 7e are available in a simple one-pot reaction by treating 1,1-dibromocyclo-propanes 5 at ?95° with BuLi and CuCl₂. Attempts towards triafulvalene precursors with good leaving groups are reported. The most promising attempt makes use of 2,2′-bis(phenylthio)-3,3′-bis(trimethylsilyl)-1,1′-bi(cyclopropylidene) (7c) which has been oxidized to give the bis(phenylsulfonyl) derivative 7g. So far, F^?-induced elimination experiments with 7g failed.     

Herstellung und Eigenschaften von Aluminiumaquoxid. III. Peptisierung von Böhmit mit Salpetersäure

Preparation and Properties of Aluminium Hydroxide. III. Peptization of Boehmite with Nitric Acid A reaction of the aluminium oxide hydroxide boehmite with nitric acid in dependence on the temperature and the molar ratio HNO₃/Al₂O₃ is studied. The effect of the acid results in the formation of basic aluminium nitrates, which can change the rheological properties of the boehmite hydrogel due to redispersion or desaggregation up to its ?liquefaction”? to boehmite hydrosol. For the dependence of the flow velocity of the boehmite hydrosol on the molar ration HNO₃ Al₂O₃ a maximum correlation is characteristic. It can also be interpreted from the colloid-chemical point of view and it is a technically relevant indicator for the optimization of the peptization. By the peptization conditions of the boehmite hydrogel the pore structure of the Al₂O₃ can be varied in a carefully directed way.     

Herstellung und Eigenschaften von Aluminiumaquoxid. II. Böhmit aus Natriumaluminat und Salpetersäure

Preparation and Properties of Aluminium Hydroxide. II. Boehmite from Sodium Aluminate and Nitric Acid A report is given on the physical-chemical characteristics of aluminium hydroxide which contain mainly boehmite, having been obtained by continuous precipitation from sodium aluminate solution with nitric acid using technical raw materials and conditions being very similar to those applied in production. The influence of the reaction conditions (pH value, temperature, concentration and residence time in the precipitation suspension) on the chemical composition, structure and texture of the hydrogels is studied. With rising precipitation temperature the pH range extends, within which already after short residence times pure-phase, relatively well crystalline boehmite hydrogels are obtained in the precipitated solution.     

Asymmetrische Michael-Additionen. Stereoselektive Alkylierung chiraler,nicht racemischer Enolate durch Nitroolefine. Herstellung enantiomerenreiner γ-Aminobuttersäure- und Bernsteinsäure-Derivate

Asymmetric Michael-Additions. Stereoselective Alkylation of Chiral, Non-racemic Enolates by Nitroolefins. Preparation of Enantiomerically Pure γ-Aminobutyric and Succinic Acid Derivatives Chiral, non-racemic lithium enolates ( E , F , G ) of 1,3-dioxolan-4-ones, methyl 1,3-oxazolidin-4-carboxylates, methyl 1,3-oxazolin-4-carboxylates, 1,3-oxazolidin-5-ones, and 1,3-imidazolidin-4-ones derived from (S)-lactic acid ( 2a ), (S)-mandelic acid ( 2b ), and (S)-malic acid ( 2c ), or from (S)-alanine ( 10 ), (S)-proline ( 11 ), (S)-serine ( 12 ), and (S)-threonine ( 13 ), are added to nitroolefins. Michael adducts ( 3 – 9 , 14 – 18 ) are formed (40–80%) with selectivities generally above 90% ds of one of the four possible stereoisomers. Conversions of these nitroalkylated products furnish the α-branched α-hydroxysuccinic acids 28 and 29 , the α-hydroxy-γ-amino acid 25 , the α,γ-di-amino acid 32 , the substituted γ-lactames 19 – 22 , and the pyrrolidine 23 . The relative and absolute configuration of the products from dioxolanones and nitropropene are derived by chemical correlation and NOE measurements indicating that the steric course of reaction is to be specified as 1k, ul-1,3. The mechanism is discussed.     

Synthese von enantiomerenreinen ‘Grasshopper’-Ketonen und verwandten Verbindungen

Synthesis of Optically Pure Grasshopper Ketone and of Its Diastereoisomers and Related Compounds Starting from our previously described synthon 1 , the synthesis of four enantiomerically pure grasshopper ketons (diastereoisomeric 4-(2′,4′-dihydroxy-2′,6′,6′-trimethylcyclohexylidene)but-3-en-2-ons) and of their oxo derivatives was performed. Spectral and chiroptical data are presented.     

Synthese, 13C-NMR-Spektren und räumliche Struktur von ‘Push-Pull’-Diacetylenen

Synthesis, ¹³C-NMR Spectra, and X-Ray Investigation of ‘Push-Pull’ Diacetylenes Phenyl-substituted ‘push-pull’ diacetylenes 1f and 1g have been prepared by acetylation and benzoylation of the appropriate lithiodiynylamines 4 (Scheme 2). ¹³C-NMR spectra of diacetylenes 1a–g (Table 1) are discussed with respect to the expected polarisation of the diacetylene unit by ‘push’ and ‘pull’ substituents. X-Ray investigations of 1c , 1e , and 1f have been performed in view of the planned solid-state polymerisation of ‘push-pull’ diacetylenes. In the crystalline state, diacetylenes 1c and 1f are stacked, however, the stacking parameters do not allow a solid-state polymerisation.     

Herstellung und Charakteristika von o-Acryloyloxy- und o-Methacryloyloxybenzoes?ure und ihren Polymeren

Ohne Zusammenfassung     

Cyclische Oligomere von (R)-3-Hydroxybuttersäure: Herstellung und strukturelle Aspekte

Cyclic Oligomers of (R)-3-Hydroxybutanoic Acid: Preparation and Structural Aspects The oligolides containing three to ten (R)-3-hydroxybutanoate (3-HB) units (12-through 40-membered rings 1–8 ) are prepared from the hydroxy acid itself, its methyl ester, its lactone (‘monolide’), or its polymer (poly(3-HB), mol. wt. ca. 10⁶ Dalton) under three sets of conditions: (i) treatment of 3-HB ( 10 ) with 2,6-dichlorobenzoyl chloride/pyridine and macrolactonization under high dilution in toluene with 4-(dimethylamino)pyridine (Fig. 3); (ii) heating a solution (benzene, xylene) of the β-lactone 12 or of the methyl ester 13 from 3-HB with the tetraoxadistanna compound 11 as trans-esterification catalyst (Fig. 4); (iii) heating a mixture of poly(3-HB) and toluene-sulfonic acid in toluene/1,2-dichloroethane for prolonged periods of time at ca. 100° (Fig. 6). In all three cases, mixtures of oligolides are formed with the triolide 1 being the prevailing component (up to 50% yield) at higher temperatures and with longer reaction times (thermodynamic control, Figs. 3–6). Starting from rac-β-lactone rac- 12 , a separable 3:1 to 3:2 mixture of the l,u- and the l,l-triolide diasteroisomers rac- 14 and rac- 1 , respectively, is obtained. An alternative method for the synthesis of the octolide 6 is also described: starting from the appropriate esters 15 and 17 and the benzyl ether 16 of 3-HB, linear dimer, tetramer, and octamer derivatives 18–23 are prepared, and the octamer 23 with free OH and CO₂H group is cyclized (→ 6 ) under typical macrolactonization conditions (see Scheme). This ‘exponential fragment coupling protocol’ can be used to make higher linear oligomers as well. The oligolides 1–8 are isolated in pure form by vacuum distillation, chromatography, and crystallization, an important analytical tool for determining the composition of mixtures being ¹³C-NMR spectroscopy (each oligolide has a unique and characteristic chemical shift of the carbonyl C-atom, with the triolide 1 at lowest, the decolide 8 at highest field). The previously published X-ray crystal structures of triolide 1 , pentolide 3 , and hexolide 4 (two forms), as well as those of the l,u-triolide rac- 14 , of tetrolide ent- 2 , of heptolide 5 , and of two modifications of octolide 6 described herein for the first time are compared with each other (Figs. 7–10 and 12–15, Tables 2 and 5–7) and with recently modelled structures (Tables 3 and 4, Fig. 11). The preferred dihedral angles τ₁ to τ₄ found along the backbone of the nine oligolide structures (the hexamer and the larger ones all have folded rings!) are mapped and statistically evaluated (Fig. 16, Tables 5–7). Due to the occurrence of two conformational minima of the dihedral angle O? CO? CH₂? CH (τ₃ = + 151 or ?43°), it is possible to locate two types of building blocks for helices in the structures at hand: a right-handed 3₁ and a left-handed 2₁ helix; both have a ca. 6 Å pitch, but very different shapes and dispositions of the carbonyl groups (Fig. 17). The 2₁ helix thus constructed from the oligolide single-crystal data is essentially superimposable with the helix derived for the crystalline domains of poly(3-HB) from stretched-fiber X-ray diffraction studies. The absence of the unfavorable (E)-type arrangements around the OC? OR bond (‘cis-ester’) from all the structures of (3-HB) oligomers known so far suggests that the model proposed for a poly(3-HB)-containing ion channel (Fig. 2) must be modified.