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Durch Reduktion der Carbonylgruppe am C-9 last sich ein, “Hilfsasymmetriezentrum” in Methylphaophorbid a (1) einfuhren. Nach Trennung der dabei entstehenden Epimeren 2 und 3 werden deren Hydroxygruppen am C-9 unter kinetisch kontrollierten Bedingungen mit racem. α-Phenylbuttersaureanhydrid acyliert. Die Interpretation der beobachteten Stereoselektivitaten gestattet es, die Chiralitat am C-10 von 1 und damit die absolute Konfiguration des Chlorophylls a abzuleiten. Die relative Konfiguration von 2 und 3 wird chemisch sowie IH-NMR- und massenspektrometrisch bewiesen. Absolute Configuration of Chlorophylls, VI1). – The Determination of the Absolute Configuration of Chlorophyll a by the Method of Horeau An auxiliary center of asymmetry can be introduced into methylphaeophorbide a (1) by reduction of the 9-carbonyl group. After separation of the resulting epimers 2 and 3, their 9-hydroxy groups are acylated under kinetically controlled conditions with a-phenylbutyric anhydride. The interpretation of the observed stereoselectivity allows deduction of the chirality at C-10 of 1 and thus the absolute configuration of chlorophyll a. The relative configurations of 2 and 3 are proved by chemical as well as 1H-NMR- and mass-spectrometric methods.

The addition of phenylmagnesium bromide to ketones derived from 2-azabieyclo[2.2.2]-octane was shown to proceed in a stereoselective manner to produce only one of two possible phenyl alcohol derivatives. Factors affecting the course of addition and the determination of relative stereochemistry of the resulting phenyl alcohols are discussed.

Prelog's rule, predicting the stereoselectivity of nucleophilic addition to the α-ketoesters of chiral alcohols, is also applicable to the reduction of α,β-ethylenic esters by LiAlH4, but this rule is no longer valid when organomagnesium halides are used as reducing agents. This difference between the two reactions is rationalized by the degree of complexation of the metallic ions of the two reducing agents in the transition states.

Ausgehend von einem geeignet substituierten Cyclohexenyl-tetrahydroharmanderivat gelang die Uberfuhrung in das pentacyclische Keton 9, uber eine Umlagerungs-Cyclisierungs-Sequenz. Reactions with Indole Derivatives, XXII. Yohimban Derivatives by Stereoselective Cyclisation Starting from an appropriately substituted cyclohexenyl-tetrahydroharmane derivative transformation into the pentacyclic ketone 9 is achieved in a rearrangement-cyclisation-sequence.

A stereoselective total synthesis of nat (−) prostaglandin E 1 and its optical antipode employing the Diels-Alder adduct of trans -piperylene and maleic anhydride as starting material is described.

To the nickel(II) complexes of 1,2-bis[2(S)-2-aminomethyl-1-pyrrolidinyl]ethane and 1, 2-bis[2(S)-2-N-methylaminomethyl-1-pyrrolidinyl]ethane, some α-amino acidate ions coordinated stereoselectively. The stereoselectivity was evaluated in terms of the ratio of stability constants, KL/KD, by measurements of circular dichroism spectra.

Treatment of α- L -fucose with sulfuryl chloride at low temperature gave mainly 2,3,4-tri- O -chlorosulfonyl-β- L -fucopyranosyl chloride ( 1 ) and a small proportion of the α-anomer ( 2 ). Both compounds adopt a 1 C 4 chair conformation. Methanolysis of 1 in the presence of silver carbonate and anhydrous calcium sulfate gave methyl 2,3,4-tri- O -chlorosulfonyl-α- L -fucopyranoside (the β-anomer being only present in small proportion), further converted into methyl α- L -fucopyranoside by treatment with a basic resin and a catalytic amount of sodium iodide. Methanolysis of 1 in the presence of sodium iodide gave directly methyl α- L -fucopyranoside, in a more rapid but less stereoselective way. Methanolysis of 2 in the presence of silver carbonate is very slow and gave, after removal of the chlorosulfonyl groups, methyl β- L -fucopyranoside with a rather poor stereoselectivity.

Epoxidation of allyl 2,3,4,6-tetra-O-acetyl-β-D-glucoside is stereoselective and gives a 7 : 3 preponderance of the (R)-epoxide; this is proved by conversion into the (R)-trithiocarbonate, followed by hydrolysis to give (R)-2,3-(thiocarbonyldithio)propan-1-ol. Epoxidation of the α-anomer is only slightly stereoselective. Conversion of the glycosidic trithiocarbonate into the dithiocarbonate (carbonyl form), followed by solvolysis, provides a new synthesis of 2,3-dimercaptopropyl glucopyranoside.

Das 4a(S), 8a(R)-Enantiomere des cis-2-Benzoyloctahydro-6(2H)-isochinolons wird durch Sporotrichum exile QM-1250 unter anaerobischen Bedingungen achtmal schneller reduziert als das 4a(R), 8a(S)-Enantiomere. Bei der entsprechenden trans-Verbindung wurde diese Stereospezifitat nicht beobachtet.

In the presence of triose phosphate isomerase, the substrate dihydroxyacetone phosphate is reduced stereoselectively by NaBH4. The reduction of enzyme-bound substrate is almost completely or completely stereoselective and occurs about one order of magnitude faster than that in free solution. This acceleration implies a polarization of the carbonyl group when dihydroxyacetone phosphate is bound.

1. The cyclization of 3-methoxy-8,14-secoestra-Δ1,2,3,(10),9(11)-tetraen-17α-ol-14-one acetate to 3-methioxyestra-Δ1,3,5(10),8,14-pentaen-17α-ol acetate (VI) proceeds via the step of isomerization of the Δ9(11)-double bond to the Δ8(9)-position. 2. The hydrogenation of acetate (VI) is not stereoselective, and gives a mixture of the 14α- and 14β-isomers, (XII) and (XI), in a 5∶4 ratio. 3. The double bond in 3-methoxy-14a-estra-Δ1,2,5,(10),8(9)-tetraen-17α-ol acetate (XII) is hydrogenated only under pressure to give the corresponding 3-methoxy-8-isoestra-17α-diol (X). In contrast, the hydrogenation of the isomeric acetate (XI) proceeds easily and leads to a mixture of the epimeric acetates (XVII) and (XVI) in a 5∶4 ratio. 4. We accomplished the total synthesis of the four isomers of the methyl ether of: 8-iso-, 9-iso-,9,14-iso-, and 8,14-isoestrones (XIV), (XV), (XVII), and (XIX).

Os(II)ClH(PPh3)3 (I) was generated and its catalytic properties were investigated. Solutions of 1 catalysed the hydrogenation of 1-alkenes, and of some internal alkenes with activated double bonds. Stereoselective cis addition of hydrogen was demonstrated with suitable model compounds. In some cases the hydrogenation reaction was accompanied by cis-trans or positional isomerization. Some reactions of 1 are reported and the nmr data of 1 and related complexes are presented.

Synthesis of the unsaturated acid 3 through H2SO4− catalysed cyclodehydration of the keto-ester 1 and its conversion to lactone 4 are described. The PPA induced cyclization of the keto-acid 9, on the other hand resulted in a stereoisomeric mixture of the octahydroanthracene derivatives 10a and 10b. The four possible racemates of the hydrofluorene derivatives 5, 6, 7, and 8 have been synthesized by chemical and catalytic reduction of 3 and 4. Li-liquid ammonia induced reductive cleavage of the lactone 4 proceeds with 65% retention and 35% inversion of configuration at the benzylic C-4a asymmetric centre to afford the trans and cis acids 5 and 8 respectively, while catalytic hydrogenolysis of 4 proceeds with inversion to give the cis acid 8. Li-liquid ammonia reduction of 3 gives trans acid 6 and cis 7 in 23% and 53% yields respectively, whereas catalytic hydrogenation of 3 affords 81% of cis acid 8 and 13% of cis acid 7. Some conformational properties of the methyl esters 17, 18, 19, and 20 have been deduced from chemical and NMR spectral data.

(+)-(R)-α(p-Tolylsulfinyl)acetophenone (I) reacts with alkyl Grignard reagents in ethyl ether to give the corresponding diastereomeric alcohols (II). The ratio of RSSC -II and RS RC-II obtained was about 7 : 3. The 1,3-asymmetric induction in this reaction is discussed.

Summary Meso- and dl-1,2-dibromo-1,2-diphenylethane are both reduced to ∼100% trans-stilbene at the mercury electrode in DMF containing 0.1 M Et4NClO4. Polarographic, coulometric and controlled-potential experiments as well as u.v. spectra substantiate a two-electron process giving the trans-olefin and Br− ions. Reduction performed in the presence of weak or strong proton donors gave the same results as in the absence of acids. Arguments in favour of a “synchronous concerted” mechanism are discussed.

The effects of the reaction conditions on the asymmetric hydroformylation of styrene with rhodium catalysts have been studied. The [α]D value and the configuration of the product, hydratropaaldehyde, were much affected by the phosphine/rhodium ratios, the reaction temperatures (20–110 °C), and the partial pressures of carbon monoxide and hydrogen (10–100 atm). The results were mainly explained in terms of the structures of the catalysts and the skeletal isomerization of acyl complexes. The predominant species of the catalysts and the participation of π-benzyl-type intermediate were also discussed.

Conditions are described for the halogenolysis of the β- and α-carbonyl-β-mercurio-peroxides RCH(OOBut)·-CH(HgX)·COR′ and XHgCH2·CMe(OOBut)·COR′, formed by peroxymercuration of αβ-unsaturated esters and ketones, to afford the previously unknown β- and α-carbonyl-β-halogeno-peroxides, respectively; eleven compounds have been characterised by elemental analysis and 1H n.m.r. spectroscopy.The peroxymercuration of methyl cis- and trans-cinnamate is shown to be stereospecific whereas both cis- and trans-chalcone give a mixture of diastereoisomers of the compound PhCH(OOBut)·CH(HgOAc)·COPh in the same proportions (1 : 4). In methanol, halogenodemercuration of the methyl cinnamate peroxymercurial, and probably also of the chalcone derivative, involves extensive racemisation, suggesting a radical or an SE1 mechanism as the major pathway.A correlation is suggested between Jαβ(and hence configuration) and the chemical shifts of t-butyl or methyl groups in the diastereoisomers of compounds of the type RCHβ(OOBut)·CHαZ·COR′ or RCHβ(OMe)·CHαZ·COR′. On the basis of this it is tentatively concluded that the greater stereoselectivity found for bromodemercuration of the compound PhCH(OOBut)·CH(HgBr)·CO2Me in dichloromethane as opposed to methanol is unexpectedly due to predominant inversion of configuration.

The cis/trans ratio of the products was studied for the platinum catalyzed hydrogenation of 4-methyl-, 4-isopropyl-, and 4-t-butylcyclohexanone in the presence of bases. Contrary to both the von Auwers–Skita rule and the results for platinum oxide catalyst already reported, addition of sodium hydroxide promoted the formation of cis-isomer.

Die chromatographische Racemattrennung von Mandelsaure an optisch aktiven Polyacryl-saureestern und -amiden von Ephedrinderivaten wurde mit 3H/14C-doppelmarkiertem Racemat untersucht. An basischen Polyacrylsaureestern von N-Alkylephedrinderivaten wird racem. Mandelsaure – wahrscheinlich uber eine Zweizentrenbindung – stereoselektiv adsorbiert, wodurch eine teilweise Auftrennung in die Antipoden erfolgt. Die Stereoselektivitat der Adsorption wird durch die Konfiguration an C-2 des Ephedrinteils bestimmt. Auch Polyacrylsaureamide von Ephedrinderivaten trennen racem. Mandelsaure teilweise auf, wobei die Stereoselektivitat im Gegensatz zu den basischen Derivaten von der Konfiguration an C-1 bestimmt wird. Die Trennleistung der Adsorbentien hangt sehr vom Polymerisations-verfahren ab. Investigation of Chromatographic Resolutions of Racemates, III. Chromatography of Racemic Mandelic Acid on Polyacrylic Esters and Amides of Optically Active Ephedrine Derivatives The chromatographic resolution of racemic mandelic acid on optically active polyacrylic esters and amides of ephedrine derivatives was investigated using the racemate composed of specifically labelled enantiomers. Polyacryl esters of N-alkylephedrine derivatives adsorb mandelic acid, resulting in partial resolution. Evidence is presented that these polymers have affinity for mandelic acid at two points. The stereoselectivity of adsorption is determined by the configuration at C-2 of the ephedrine portion. Also, polyamides of ephedrine derivatives affect a partial resolution of mandelic acid. In contrast to the basic derivatives, the stereoselectivity is determined by the configuration at C-1. The separation efficiency of these adsorbents is highly dependent on the polymerisation procedure.

The experimental verification of a proposed biosynthetic pathway for a given natural product is often difficult to obtain with the use of the whole organism (permeability factors) or, in the case of higher plants, a cell-free system. Until the purified enzyme for each step of biosynthesis is available, biosynthetic studies can, however, be carried out, albeit with modest incorporation values, by means of either hydroponic or injection methodology. Where viable seed sources are available it is suggested that improvements of several orders of magnitude in incorporation can be achieved by a short-term incubation (small pool size of precursors; trapping of reactive intermediates) or a long-term feeding (equilibration of precursor with the compartmentalized or induced synthetases). In bacterial, fungal, mammalian, and plant systems, where incorporation efficiencies provide the opportunity to study (13)C enrichment (at least equal to natural abundance of the isotope), we can expect a rapid expansion since the method removes the tedium of carbon-by-carbon degradation. For the next few years, however, the prognosis would seem to favor parallel studies of (13)C and (2)H, and of (14)C/(3)H ratio techniques since the last-mentioned method provides more information concerning the stereoselectivity of labeling processes on the microgram scale.

The complex [Co(ox)(L-aspH)(en)] has been prepared by the reaction of the dioxalatoethylenediaminecobalt-(III) complex with L-aspartic acid and separated into four diastereoisomers by means of ion-exchange chromatography: mer-Δ-, mer-Λ- and facΔ-[Coox(L-aspH)en]·H2O, and facΛ-[Coox(L-aspH)en]·2.5H2O. They were characterized by their absorption, CD and PMR spectra. Stereoselectivity has been found in the mer-Δ and fac-Λ isomers with degrees exceeding 80%. Related isomeric complexes containing L-glutamate or L-leucinate ion in place of L-aspartate have also been investigated, much less selectivity (∼60%) being observed.

Tricyclo[5.3.1.03,8] undecane (II), which would be conveniently refered to by the trivial name 4-homoisotwistane in accordance with Majerski's nomenclature,1 was first prepared by Krantz2 during the stereoselectivity study on intramolecular Diels-Alder reactions of 5-alkenylcyclohexa-1,3-dienes, and recently discovered independently by Schleyer,3 Majerski1 and us4 to be involved as a reasonably stable intermediate in acid-catalyzed isomerization of various tricycloundecane precursors to equilibrium mixtures of 1 and 2-methyladamantanes.

The stereochemistry ( anti or syn mode) of dehydrohalogenation of 2,3-dibromo-butane, 2,3-dichlorobutane and 2-bromobutane over MgO, CaO, SrO and Al 2 O 3 was determined by use of a pulse technique from the products of the diastereomeric isomers of each compound at 100–250 °C. The elimination of hydrogen halide proceeded selectively by anti mode over fresh surface of these oxides below 200 °C for dibromobutane and below 250 °C for dichlorobutane, reflecting the surface basicity. Anti mode was also favored in the case of 2-bromobutane at about 100 °C. However, due to the alteration of surface basicity by hydrogen halide formed, the stereoselectivity decreased with repeated pulses. Present results agree with the idea deduced previously in the case of silica gels that the acid-base properties of catalyst and substrate are the prime factor controlling the steric course of reactions. Stereochemistry of debromination and halogen-substitution reactions of dibromobutane, the accompanying reactions, was also determined to be anti mode and retention, respectively.

The stereochemistry of reduction of acyclic ketones with tributyltin hydride under ionic or flee-radical conditions has been established. The results are discussed using the usual models of asymmetric induction. The stereochemistry of the products is little affected by the hydrostannation mechanism and the stereoselectivity in both cases is minor.

Tris(N-(R- or S-)α-phenylethyl-5-nitrosalicylaldiminato)chromium(III) and tris(N-S-α-benzylethyl-5-nitrosalicylaldiminato)rutheniurn(III) have been prepared, and two diastereomers for each complex have been isolated. Relative configurations of the Cr(III) diastereomers and their Co(III) analogs, which were reported previously, are assigned from a comparison of CD spectra and chromatographic behavior. Assignments of configuration of the Ru(III) diastereomers relative to the analogous Co(III) and Cr(III) diastereomers are based on the similarity of chromatographic behavior for these species. Empirical relationships among low-energy CD bands for Co(III), Cr(III), and Ru(III) salicylaldimine complexes believed to have the same configuration are discussed and predictions of absolute configuration of diastereomers in this series are made from stereoselectivity observations.

Pfeiffer effect was studied in aqueous solutions containing tris(phenanthroline)metal(II) (metal=zinc or nickel) complexes and various alkaloids. The results were interpreted quantitatively from the viewpoint of stereoselective association and the resulting equilibrium shift. The contribution of π-π interaction between the complex and the alkaloid conjugate systems to the stereoselective association is suggested. NMR data were found to be consistent with the π-π interaction. Relation between the sign of the Pfeiffer rotation and the absolute configuration of the complex is presumed.

The stereoselectivity on the addition reaction of nucleophiles (CH3O− and PhCH2S−) to three model compounds, 6-deoxy-1,2-o-isopropylidene-6-nitro-3-o-substituted-α-D-xylo-hex-5-enofuranoses (1a, 1b and 1c) was examined in terms of six control parameters.

The results of a microbial survey study have shown that the ability to reduce added ketopantoic acid (or ketopantoyl lactone) and accumulate pantoic acid (or pantoyl lactone) in the growth medium is widespread among diverse fungi. The reductions generally proceeded with less than full stereoselectivity. However, specific strains of the ascomycete Byssochlamys fulva were found to form D[-]-pantoic acid in unusually high yields and optical purity.

2,3,4,6-Tetra-O-benzyl-α- d -gluco- and -α- d -galactopyranosyl iodides react rapidly in acetonitrile and other solvents with limited excesses of methanol, ethanol, 2-propanol, and cyclohexanol in the presence of 2,6-lutidine. The products obtained from the lower alcohols, contain a high proportion of α glycoside. The highest ratios of α- to β-anomer are obtained at low concentrations of alcohol. The high rates, stereoselectivity, and lack of side-reactions observed suggest that the alcoholysis of glycosyl iodides should be tested as a route to oligosaccharide synthesis.

In fat cells, with the aid of stereoisomers of norepinephrine, a correlation between the initial events in the drug-receptor interactions and the end pharmacologic effect was sought. In the presence of theophylline, the isomeric activity difference for the rise in intracellular cyclic AMP was 2.5 log units. The rise presumably occurs through the stereoselective interaction of the isomers at the β-adrenergic receptor and/or adenylate cyclase. The isomeric activity difference for the lipolysis, an end pharmacologic effect, was the same, 2.5 log units. Although the stereoselective rise in cyclic AMP indicates that the event preceding the rise must also be stereoselective, the incubation of (−)- or (+)-norepinephrine with (−)-3H-norepinephrine with fat cell membrane particles failed to show the selectivity in binding. The methodological problems for such failure are discussed.

1. The hydrogenation of the methyl ester ofα-acetamidocinnamic acid over Pd-black and sketetal Ni, modified by optically active copolymers of styrene with alanine maleimide, gives an optically active phenylalanine with an optical purity of 1–2%. 2. The modification of Pd-black by aqueous solutions of optically active copolymers revealed that the modification pH affects not only the value, but also the sign of rotation of the formed phenylalanine. 3. The value and character of the catalyst stereoselectivity as a function of the modification pH is explained by the formation of various types of complexes on the catalyst surface, due to the configurational and conformational changes in the optically active polyelectrolyte as a function of its degree of dissociation.

The history of and need for asymmetric syntheses are reviewed briefly with special mention of recently developed methods of high efficiency. The conditions for a viable asymmetric synthesis are stated. Highly stereoselective syntheses involving sulfonium salts and 1,3-dithianes are detailed.

1. Using peroxide initiation and UV irradiation, the dimerization rate of 2,3,3-trichloropropene was studied in the range 50–70‡. 2. The dimerization is stereoselective, with the predominant formation of trans-1,2,4,5-tetrachloro-4-dichloromethylpentene. A reaction scheme was proposed that satisfies the obtained experimental data.

The lack of stereoselectivity in the Stobbe condensation involving acetophenone or diethyl α-phenylethylidene-succinate can be attributed to E2 elimination through both diastereoisomeric lactone intermediates, base catalysed isomerisation of ester reactant or product(s), or a combination of these reactions.

(1973). AN IMPROVED STEREOSELECTIVE REDUCTION FOR THE PREPARATION OF endo-7-PHENYLNORCARANE. Organic Preparations and Procedures International: Vol. 5, No. 6, pp. 275-279.