bluuebunny/crossref_metadata_2025_split huggingface dataset:
Herstellung und Reaktionen der valenzpolaromeren Verbindung (4,4‐Dimethyl‐2‐thiazolin‐5‐dimethyliminium)‐2‐thiolat ⇌ (1‐Dimethylthiocarbamoyl‐1‐methyl‐äthyl)‐isothiocyanat aus 3‐Dimethyl‐amino‐2,2‐dimethyl‐2H‐azirin und Schwefelkohlenstoff
Authors: Chaloupka Stanislav , Heimgartner Heinz , Schmid Hans , Link Helmut , Schönholzer Peter , Bernauer Karl 
Published: December 2004

Synthesis and reactions of the valence polaromeric compound (4,4‐dimethyl‐2‐thiazoline‐5‐dimethyliminium)‐2‐thiolate ⇌ 1‐dimethylthiocarbamoyl‐1‐methyl‐ethyl isothiocyanate from 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine and carbon disulfide.3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) reacts with carbon disulfide to give crystals which have the dipolar structure 3a [(4,4‐dimethyl‐2‐thiazoline‐5‐dimethyliminium)‐2‐thiolate, Scheme 1]. In solution, the non‐dipolar (charge‐free) isomeric form 3b (1‐Dimethyl‐thiocarbamoyl‐1‐methyl‐ethyl isothiocyanate) is almost exclusively populated. Reaction products are derived from both forms: Derivatives of 3a are the hydrolysis product 6, the sodium borohydride reduction product 7 and the methylation products 9 and 10, respectively (Scheme 2). The isothiocyanate form 3b is responsible for the various reaction products with amines (Scheme 3). One of the reaction products with ammonia, namely 20, is also obtained by the reaction of 1 with thiocyanic acid.Thermolysis of the azirine/carbon disulfide adduct 3 leads to 2‐dimethylamino‐4,4‐dimethyl‐2‐thiazoline‐5‐thione (17) in high yield. A possible mechanism is outlined in Scheme 4. The same compound is also formed by rearrangement of 3 under the catalytic influence of dimethylamine. Its structure has been established by X‐ray crystallography (section 4). Again a rearrangement is involved in the reductive (NaBH4) conversion of 17 to 7, the direct reduction product of the dipolar species 3a (Scheme 5).The isothiocyanate form 3b is able to react with a second molecule of 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) to yield compound 25, which in the crystalline or dissolved state appears to be almost entirely populated by the carbodiimide form with structure 25b (Scheme 7), though all reaction products of 25 (reduction with sodium borohydride, addition of water or hydrogen sulfide, Schemes 7 and 8) are derived from the dipolar form 25a, not detectable as such; here again therefore there is a dynamic equilibrium 25a ⇌ 25b.The two forms of adduct 3, namely 3a and 3b, are obviously very easily interconverted at room temperature and therefore can be considered as valence polaromeric forms (section 5). A classification of the dipolar (zwitterionic) form is given, which allows a comparison of various dipolar species and gives as indication of charge stabilization by delocalization.The versatile reactivity of the 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine/carbon disulfide adduct is demonstrated by the fact that with simple reagents approximately 25 derivatives have been obtained, most of them being new heterocyclic compounds.
Zur Reaktion zwischen Bis (dimethylamino)acetonitril und Phenylisocyanat. Vorläufige Mitteilung
Authors: Seckinger Karl 
Published: December 2004

On the Reaction of Bis(dimethylamino)acetonitrile with PhenylisocyanateBis(dimethylamino)acetonitrile (1) reacts with phenylisocyanate to yield the imidazolidinedione 2, as confirmed by X‐ray structure analysis. The mechanism of formation of 2 is discussed.
Reaktion von 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirin mit Barbitursäure
Authors: Link Helmut , Bernauer Karl , Daly John J. , Chaloupka Stanislav , Heimgartner Heinz 
Published: December 2004

Reaction of 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine with Barbituric AcidThe reaction of 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) with barbituric acid (4) in dimethyl formamide at room temperature yields a mixture of several compounds. The two main products 5 and 6 have been isolated in 40 and 10% yield, respectively, and their structures established by X‐ray analysis. In Schemes 4–6 reaction mechanisms for the formation of 5 and 6 are postulated, the first step beeing either a C‐ or an N‐alkylation of barbituric acid.Reduction of 5 and 6 with NaBH4 in ethanol at room temperature yields 6,6‐dimethyl‐1,5,6,7‐tetrahydro‐pyrrolo[2,3‐d]pyrimidin‐2,4(3H)‐dione (7) and 3,3‐dimethyl‐2,3‐dihydro‐imidazo[1,2‐c]pyrimidin‐5,7(1H, 6H)‐dione (8) in 38 and 48% yield, respectively. Treatment of 6 with 3N aqueous NaOH at room temperature gives 3,3‐dimethyl‐imidazo[1,2‐c]pyrimidin‐2,5,7 (1H, 3H, 6H)‐trione (9) in 51% yield (Scheme 3).
Halogenierte Cyclobutanone als variationsreiche Vorläufer von Pyrethroiden: Synthesen durch [2+2]‐Cycloadditionen von Haloketenen an 1,1‐disubstituierte Äthylene
Authors: Martin Pierre , Greuter Hans , Belluš Daniel 
Published: December 2004

Halogenated Cyclobutanones as Highly Versatile Precursors of Pyrethroids: Syntheses via [2+2]‐Cycloadditions of Haloketenes to 1,1‐Disubstituted Ethylenes[2+2]‐Cycloaddition reactions of the new chloro‐(2,2,2‐trichloroethyl)ketene (9) with various 1,1‐disubstituted ethylenes as well as [2+2]‐cycloadditions of highly halogenated ketenes of type 32 are described. The halogenated cyclobutanones thus obtained represent valuable intermediates in a new synthesis of insecticidal pyrethroids (Scheme 1). Ketene 9, prepared in situ from readily available precursors, parallels, if not exceeds, dichloroketene in its reactivity. With isobutene, the cyclobutanone 10 (a precursor for cis‐3‐(2,2‐dichlorovinyl)‐2,2‐dimethylcyclopropane carboxylic acid) is obtained in 70% yield. The reaction of 9 with propene is stereospecific and leads to cis‐17, exclusively. This result may be explained in terms of the energetically most favourable approach of the reacting molecules in a [π2s + π2s] process.
Euphroside, A New Iridoid Glucoside from Euphrasia salisburgensis HOPPE
Authors: Sticher Otto , Salama Osama 
Published: December 2004

AbstractFive iridoid glucosides have been isolated from the whole plant of Euphrasia salisburgensis. The structure of the new compound, named euphroside, and the identity of the others have been established by chemical transformations and spectral data.
Die absolute Konfiguration von Macrolin, einem Abbauprodukt des Alkaloides Villalstonin 179. Mitteilung über organische Naturstoffe
Authors: Neukomm Gisela , Kletzhäundler Erika , Hesse Manfred 
Published: December 2004

The Absolute Configuration of Macroline, a Degradation Product of the Alkaloid VillalstonineThe absolute configuration of macroline (1), a degradration product of villalstonine (2), was determined. The chemical degradation of 1 gave a mixture of (–)‐(20S)‐20,21‐dihydro‐19‐desoxo‐macroline (9) and (–)‐(20R)‐20,21‐dihydro‐19‐desoxo‐macroline (10), which was related to the degradation products 9 of (+)‐ajmaline (3) and 10 of (+)‐isoajmaline (4) of known absolute configuration. Together with the complete relative stereochemistry of 2 the absolute configuration of 2 and of the second moiety of 2, (+)‐pleiocarpamine (20), could be derived. Since the absolute configuration of the (–)‐6, 7‐dihydroaspidospermidine moiety of (+)‐pycnanthinine has been known already [15], the structure by Gorman et al. [17] represents the absolute configuration of (+)‐pycnanthinine.
Electronic Absorption and Emission Spectra of 1, 3‐Diaryltriazenes
Authors: Páarkányi Cyril , Vernin Gaston , Julliard Michel , Metzger Jacques 
Published: December 2004

AbstractThe Pariser‐Parr‐Pople (PPP) type LCI‐SCF‐MO calculations were used to study the models of 1, 3‐diphenyltriazene (1), 1, 3‐bis(3‐pyridyl)triazene (2), 1, 3‐bis (2, 4‐dichlorophenyl)triazene (3), and 1, 3‐bis (4‐ethoxycarbonyl)triazene (4). The results of the calculations were compared with the experimental electronic absorption and emission (fluorescence, phosphorescence) spectra of these compounds.
Macrocyclische Spermidinalkaloide aus Pleurostylia africana LOES. 9. Mitteilung über Celastraceen‐Inhaltsstoffe
Authors: Wagner Hildebert , Burghart Josef 
Published: December 2004

Macrocyclic Spermidine Alcaloids from Pleurostylia africana LOES.The structure of pleurostyline, a new macrocyclic spermidine alkaloid from Pleurostylia africana (Celastraceae), has been elucidated mainly by 1H‐ and 13C‐NMR.‐spectroscopy. Pleurostyline represents a new structure type in which spermidine is incorporated in a 13‐membered lactam ring to which an additional cinnamoyl residue is fused to yield a 7‐membered ring. The same plant contains also the spermidine alkaloids celacinnine and cellallocinnine of which 13C‐ and high field 1H‐NMR.‐measurements have been carried out for the first time. Both alkaloids are interconvertible by UV.‐irradiation. In addition the existence of rotational isomerism of one amide group of these alkaloids has been demonstrated by NMR.‐spectroscopy.
Desorption/Chemical Ionization Mass Spectrometry of Naturally Occurring Glycosides
Authors: Hostettmann Kurt , Doumas Jacques , Hardy Michel 
Published: December 2004

AbstractDesorption/chemical ionization mass spectrometry (D/CI.‐MS.) is a recently developed technique especially indicated for highly polar and non volatile compounds. Various naturally occurring glycosides such as saponins, iridoid and secoiridoid glycosides, cardenolides and flavone‐O‐glycosides have been investigated by this method. All the measurements were carried out on underivatized compounds. In addition to the structural informations generally furnished by field‐desorption mass spectrometry (molecular ion and sugar sequence), the molecular ion and pertinent fragments of the aglycone could also be obtained.
Computer Assisted Structural Interpretation of Mass Spectral Data
Authors: Gray Neil A. B. , Buchs Armand , Smith Dennis H. , Djerassi Carl 
Published: December 2004

AbstractAn interactive system of programs has been developed to assist in structure elucidation based on mass spectral data. The program relies on algorithms for generating all the structural isomers that constitute alternative explanations of the observed data and it associates relative plausibility values with the different isomers. The structure assembly part of the program allows for the use of overlapping substructural components, such as substructures inferred from the appearance of particular ion patterns in the spectrum of an unknown compound. Mass spectrum interpretation procedures used with this structure assembly process could exploit any form of spectrum‐substructure correlation scheme. In this work, the emphasis has been on the use of detailed and class specific spectrum‐substructure correlations. Applications of the program are illustrated by means of an example analysis of the mass spectra of a variety of marine sterols.
Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Polyamines, in Relation with the Chelate Effect
Authors: Delville Alfred , Detellier Christian , Gerstmans André , Laszlo Pierre 
Published: December 2004

AbstractThe problem of determining the chelate effect brushes against methodological snags: the choice of concentration units, and of the appropriate standard states. We avoid these pitfalls by defining the chelate effect from measurements on bidentate ligands alone, without recourse to comparison with the corresponding unidentate ligands. Quantitation of the parameters extracted from the data is effected by three independent and mutually consistent procedures. Solvation of the Na+‐cation by the polyamines follows the sequence: cadaverin < 1, 3‐diaminopropane ≪ ethylene diamine ≪ diethylenetriamine. Entry of the first and of the second diamine molecule into the sodium coordination shell are independent and equiprobable steps: K1 = K3 and K2 = K4, within the accuracy of the measurements. For ethylene diamine, the values of K1 and K3 are in the range 1.0–1.5 and those for K2 and K4 are in the range 83–102: attachment of the second N‐atom is considerably easier, by two orders of magnitude (chelate effect). The chelate effect is strongly reduced in cadaverin, with a longer hydrocarbon chain connecting the two amine functions.
Studies of molecular ions. IX. Detection of low‐lying ‘non‐Koopmans’ states in polyacetylene molecular cations
Authors: Haselbach Edwin , Klemm Urs , Buser Urs , Gschwind Rudolf , Jungen Martin , Kloster‐Jensen Else , Maier John P. , Marthaler Oscar , Christen Heniz , Baertschi Peter 
Published: December 2004

AbstractComparison of the photoelectron spectra of the title compounds with the electronic absorption spectra of the corresponding radical cations led to the detection of low lying ‘Non‐Koopmans’‐states in the ionic species.
1‐Aryl‐ und 1‐Alkyl‐2‐phthalimido‐diazen‐1‐oxide, diacylierte Vertreter von trisubstituierten Triazen‐1‐oxiden: Bildung, Eigenschaften, Stereoisomerisierung und Fragmentierung
Authors: Hoesch Lienhard , Köppel Bruno 
Published: December 2004

1‐Aryl‐ and 1‐Alkyl‐2‐phathalimido‐diazene‐1‐oxides, Diacylated Examples of Trisubstituted Triazene‐1‐oxides: Formation, Properties, Stereoisomerization and Fragmentation1)Oxidatively generated phthalimido‐nitrene (1) reacts with nitrosobenzene (8a), p‐nitrosotoluene (8b), o‐nitrosotoluene (8c), p‐dimethylamino‐nitrosobenzene (8d), p‐methoxycarbonyl‐nitrosobenzene (8e), 1, 1‐dimethyl‐1‐nitrosoethane (8f) and nitrosocyclohexane (8g) to give the respective 1‐substituted (Z)‐2‐phthalimidodiazene‐1‐oxides 14a‐g.The constitution of 2‐imidodiazene‐1‐oxides 14 is deduced from their spectroscopic properties. The UV. spectra of 14a‐e are similar with those of the corresponding nitrobenzenes 18, thus supporting the concept of comparibility of the phthalimido‐N group with an O‐atom and indicating that the phthalimido group is not in conjugation with the diazene‐oxide function.This is in contrast to the situation in the non‐acylated trisubstituted triazene‐1‐oxides 12, where conjugation is extended over the chain of all three N‐atoms as exhibited by the UV. spectra of (Z)‐1, 3, 3‐triphenyl‐, (Z)‐3, 3‐dimethyl‐1‐phenyl‐, (Z‐3‐methyl‐1, 3‐diphenyl‐, (Z)‐1‐(1, 1‐dimethylethyl)‐3, 3‐diphenyl‐, and (Z)‐1‐(1, 1‐dimethylethyl)‐3, 3‐dimethyltriazene‐1‐oxide (12a‐e). These triazene‐1‐oxides are formed by the reaction of 1, 1‐disubstituted hydrazines 11 with three mol‐equiv. of nitroso compounds 8 or from equimolar amounts of 11 and 8 in the presence of mercury oxide. Over 90% of 1, 2‐diphenyldiazeneoxide (19, R = C6H5) are isolated by the reaction 11 + 3 8a. Possible mechanisms of the reaction of 11 with 8, and of the formation of 12 via triazanols D and of 19 (R = C6H5) via N‐Phenylhydroxylamine (20, R = C6H5) are given in Scheme 6 (in the latter case with experimental evidence). An independent synthesis of 12c confirms the constitutional assignment for 12.
Ein neuer Zugang zum tetracyclischen Grundgerüst des Cyclohepta (def)fluorens
Authors: Neidlein Richard , Kramer Walter 
Published: December 2004

A New Synthetic Way to the Tetracyclic Skeleton of Cyclohepta (def)fluoreneThe synthesis of 2‐Methyl‐4, 5, 6, 8, 9, 10‐hexahydrocyclohepta (def)fluorene 2 is described starting with the reduction of the ketone 3 by a (1:1)‐mixture of LiAlH4/AlCl3 to the hydrocarbon 4. After metallation with butyllithium 4 was allowed to react with bromoacetic acid to yield 5. The cyclization of this compound was performed with p‐toluenesulfonic acid to give the tetracyclic ketone 6 which was converted to the tetracyclic hydrocarbon 2 by reduction with LiAlH4/AlCl3.
Steroids and Sexhormones. Part 265. Limonin, Part VI. Synthesis of a model compound incorporating rings D and E of 14,15‐deepoxylimonin
Authors: Emmer Gerhard , Graf Walter 
Published: December 2004

AbstractStarting from the known formyl ketene thioacetal 6, model compound 11 was synthesized. The key intermediates, the epimeric furylmethanols 7a and 7b, were converted into the same dithioortholactone 8b (Scheme 1) and further elaborated into the model compound 11 (Scheme 2), a versatile compound in the synthesis of limonin (1). The acid catalyzed conversion of the epimers 7a and 7b into 8b may probably involve a hydride‐transfer reaction with inversion of configuration at C(17) of alcohol 7a (Scheme 4, row b).
Aufbau der Ligandsysteme des C, D‐Tetradehydrocorrins und Isobakteriochlorins durch Sulfidkontraktion. Kurzmitteilung
Authors: Ofner Silvio , Rasetti Vittorio , Zehnder Beat , Eschenmoser Albert 
Published: December 2004

Synthesis of C, D‐Tetradehydrocorrins and Isobacteriochlorins via Sulfide ContractionThe reaction sequences shown in Schemes 4 and 5 illustrate the use of the sulfide contraction method for the synthesis of isobacteriochlorins and (metal free) C, D‐tetradehydrocorrins. The tetradehydrocorrin synthesis fills a gap in a spectrum of corrinoid (A → D) ring closures that ranges from A.W. Johnson's oxidative (A → D)‐cyclizations to octadehydrocorrinoids on the one side to the photochemical 1, 19‐secocorrin → corrincycloisomerization on the other (Scheme 7). Such a multiplicity of reaction paths towards corrinoids is of interest in connection with the problem of the origin of the corrin structure.
Etude de la fragmentation par impact électronique en ions positifs et négatifs de dérivés nitrés de l'amino‐2‐benzothiazole
Authors: Claude Saturnin , Tabacchi Raffaele , Duc Laurent , Marrel Jean‐François 
Published: December 2004

Study of Positive and Negative Ions Electron Impact Fragmentation of 2‐Amino‐benzothiazole Nitro DerivativesThe positive and negative ions mass spectra of 2‐amino‐4,6‐dinitrobenzothiazole (1), 2‐amino‐4‐nitrobenzothiazole (2), 2‐amino‐6‐nitrobenzothiazole (3) are reported and discussed. These compounds give an intense molecular ion and show interesting fragmentations in both positive and negative ions spectra. Specific 15N‐labelling was used in order to confirm the fragmentation patterns.
Chemical Selectivities Disguised by Mass Diffusion. VIII. Influence of pH‐gradients on the product distribution in mixing‐disguised azo coupling reactions. 9th Communication on the selectivity of chemical processes
Authors: Belevi Hasan , Bourne John R. , Rys Paul 
Published: December 2004

AbstractIn mixing‐disguised azo coupling reactions the protons which are released during the electrophilic substitution steps cause a pH‐gradient in the reaction zone. Since, owing to the acid‐base pre‐equilibria, these pH‐gradients also determine the local concentrations of the reactants in the reaction zone, they also have an influence on the measured product distribution of such fast reactions. In the present work, the product distribution of the azo coupling of 1‐naphthol with 4‐sulfophenyldiazonium ion was experimentally measured and the results were compared with the distributions predicted from our mixing‐reaction model developed previously [1]. Furthermore, some experimental evidence for the existence of isoselectivity points are presented, at which a change of the initial pH‐value has no influence on the product distribution.
Chemical Degradation of Lasalocid: (A) The Mannich reaction (B) Baeyer‐Villiger oxidation of the retro‐aldol ketone
Authors: Coffen David L. , Katonak David A. 
Published: December 2004

AbstractUnder Mannich reaction conditions (diethylamine and formaldehyde in toluene under reflux) lasalocid (1) undergoes a unique transformation in which the carboxyl group is replaced by a diethylaminomethyl group. The resulting Mannich base 2 was converted back to lasalocid, proving that none of the other chemical and stereochemical features of the molecule were disturbed. Like other phenolic Mannich bases, the one derived from lasalocid readily alkylated mercaptans.The known thermal and base‐induced retro‐aldol degradations of lasalocid both produce a ketone fragment 9 containing the cyclic ether units. Baeyer‐Villiger oxidation of this ketone afforded a carboxylic acid fragment which still contained these ether units. The normal regiochemistry involved in oxidizing this ketone (RCH2COCHR′R″ type) was cleanly reversed by first converting it into the hydroxymethylidene derivative 10.
Structure Determination of Brominated Morphinan‐6‐ones by 13C‐NMR. Spectroscopy: A novel closure of the oxygen bridge using 4‐acetoxymorphinan‐6‐ones
Authors: Brossi Arnold , Hsu Fu‐Lian , Rice Kenner C. , Rozwadowska Maria D. , Schmidhammer Helmut , Hufford Charles D. , Chiang Chian Chian , Karle Isabella L. 
Published: December 2004

AbstractBromination of (−)‐4‐hydroxy‐N‐methylmorphinan‐6‐one (3), prepared from natural morphine, with 1 mol of bromine in acetic acid, afforded the 1‐bromo ketone 5. The structure of 5 was assigned by 13C‐NMR.spectroscopy, and confirmed by X‐ray diffraction analysis of its hydrobromide salt. It is suggested that monobromination of synthetic (±)‐2,4‐dihydroxy‐N‐formylmorphinan‐6‐one (7) takes in principle a similar course, although the 13C‐NMR.spectrum of the primary reaction product 9 could not be measured because of insolubility in commonly used solvents. Monobromination of (−)‐4‐acetoxy‐N‐formylmorphinan‐6‐one (12) of the natural series, and of (±)‐2,4‐diacetoxy‐N‐formylmorphinan‐6‐one (8) of the synthetic series, followed by treatment of the monobrominated ketones with potassium carbonate in methanol resulted in closure of the O‐bridge, and afforded after acid hydrolysis, the corresponding 4,5‐epoxy‐morphinan‐6‐ones (−)‐16 and (±)‐17 respectively. This variation of the ring closure reaction represents a novel and convenient method to convert 4‐hydroxymorphinan‐6‐ones into their corresponding 4,5‐epoxymorphinan‐6‐ones, without involving aromatic bromination and with only 1 mol of bromine.
Structure Elucidation and Synthesis of Flavonol Acylglycosides. III.. The synthesis of tiliroside
Authors: Vermes Barbara , Chari Vedanta Mohan , Wagner Hildebert 
Published: December 2004

AbstractNaturally occurring kaempferol 3‐O‐β‐D‐(6″‐O‐coumaroyl)glucopyranoside (tiliroside) has been synthesized thereby confirming its structure. This is the first acylated flavonoid glycoside to be synthesized.
Ionization Energies of Methyl‐substituted[2.2]Paracyclophanes
Authors: Zhong‐zhi Yang , Kovač Branka , Heilbronner Edgar , Eltamany Sayed , Hopf Henning 
Published: December 2004

AbstractThe photoelectron (PE.) spectra of thirteen methyl‐substituted [2.2]paracyclophanes have been recorded and analyzed, to assess the influence of methyl‐substitution on their ionization energies. It is shown that this influence is qualitatively and quantitatively the same as for benzenes and other π‐systems. Comparison with the previous results obtained for the [2r]cyclophanes (r=2 to 6) strongly suggests that the hyperconjugative model for alkyl‐group/π‐system interactions is more appropriate than the inductive one.
Carbon Participation in the Solvolysis of 6‐endo‐Substituted 2‐exo‐Norbornyl Toluenesulfonates. Norbornanes part 6
Authors: Grob Cyril A. , Günther Bettina , Hanreich Reinhard 
Published: December 2004

AbstractThe solvolysis rate constants k for the 6‐endo‐substituted 2‐exo‐norbornyl toluenesulfonates 7 have been determined. Values of logk correlate well with the respective inductive constants of the substitutents except when the latter are nucleophilic and therefore lead to endo‐cyclization, or when they are n‐electron donors and cause concerted fragmentation. In general 6‐endo‐substituted tosylates 7 react somewhat more slowly than their 6‐exo‐epimers.Identical or different mixtures were obtained from the C(6)‐epimers 7 and 1 depending on whether the substituent was an electron donor or acceptor. It is concluded that donor substituents at C(6) enhance 1,3‐bridging in the intermediate epimeric cations and lead to their rapid and complete equilibration, and that electron acceptors reduce bridging and hence their equilibration rates.
Enantioselective Addition of Chiral Organotitanium Derivatives to Aldehydes
Authors: Olivero Alan G. , Weidmann Beat , Seebach Dieter 
Published: December 2004

AbstractAlkoxy‐ and aryloxy‐organotitanium compounds 2–4 derived from (S)‐2‐methyl‐1‐butanol, (R)‐2‐butanol, (‐)‐menthol, quinine, cinchonine, and (S)‐1.1′‐binaphthol are added to aromatic aldehydes to give optically active alcohols 5–10 in enantioselectivities of up to 88% e. e., with nucleophilic transfer of methyl, phenyl, and 1‐naphthyl groups. The Tables 1–3 list the effects of varying the reagents, the substrates, and the reaction conditions of the new asymmetric synthesis.