bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic study of the oxidation of 1,4‐dihydropyridines with chloranil
Authors: Dommisse R. A. , Lepoivre J. A. , Alderweireldt F. C. 
Published: September 2010

AbstractThe reaction kinetics of the redox system chloranil‐1, 4‐dihydropyridine (of the Hantzsch‐ester type) is monitored by U. V.‐spectroscopy. A possible reaction mechanism is discussed. Evidence for an ion‐pair formation in a purely second‐order reaction is given. Some catalytic effects are described. From the thermodynamic parameters it is clearly demonstrated that the electronic effects of the substituents are of an utmost importance. All reactions have large negative ΔS≠‐values.The reduction of several functional groups with 1, 4‐dihydropyridines have recently been intensively studied especially as test‐case reactions for the coenzymes NADH and NADPH. Up to now only a limited amount of data on reaction velocities has been published (1). In the present paper the oxidation of several Hantzsch‐esters (see table 1) is described with emphasis on reaction kinetics and structural effects. Chloranil is choosen as a suitable oxidans for practical purposes. A reaction mechanism is given for the well known reaction (fig. 1).
Photobromination of Halogenobenzenes: Ipso‐Attack or Not?
Authors: Gouverneur P. , Soumillion J. P. 
Published: September 2010

AbstractIn a preliminary communication (2) we reported the results obtained in the photo‐ and ionic brominations of halogeno‐ and dihalogenobenzenes. A recent paper(3) suggested that our results “are suggestive of ipso‐attack, a mechanism that has not previously been advocated for free‐radical reactions”. The purpose of this communication is to point out that the proofs of such a mechanism are not borne out by our data. This does not imply that ipso‐attack has to be rejected but it needs other data to be proved and remains only a simple although attractive hypothesis.
Potentiometric Study of Hydrogen Chloride in 2‐Methoxyethanol Water Mixtures
Authors: Merken G. V. , Thun Harry P. , Verbeek F. 
Published: September 2010

AbstractThe standard emf of the cell Pt;H2/HCl(solvent)/AgCl, Ag |1| is reported for the mixtures 80, 90, 95 and 98 wt‐% 2‐methoxyethanol and respectively 20, 10, May and February wt‐% water. The correlation of the present and previous results enables to present a structure for solutions of hydrogen chloride in mixtures of 2‐methoxyethanol and water.
Rearrangement of α‐Chloro‐Isobutyraldimines: Synthesis of 2‐Imidazolidinones
Authors: De Kimpe Norbert , Verhe Roland , De Buyck Laurent , Schamp Niceas 
Published: September 2010

AbstractTreatment of N‐1‐(2‐chloro‐2‐methylpropylidene) amines with potassium cyanate in methanol afforded 1‐substituted‐4‐methoxy‐5,5‐dimethyl‐2‐imidazolidinones, which were easily converted into the non‐methoxylated derivatives, i.e. 1‐substituted‐5,5‐dimethyl‐2‐imidazolidinones, by reaction with lithium aluminium hydride in diethyl ether. The structure was confirmed by independent synthesis of the latter heterocycles and their isomeric structure (4,4‐dimethyl derivative). The formation of the 2‐imidazolidinones, starting from α‐chloroaldimines and potassium cyanate, involved a rearrangement of the imino‐nitrogen atom, which was explained by an aziridine intermediate.
Réactions De Deshydrodimérisation Radicalaire. 4. Action Du Peroxyde De Di‐t.Butyle Sur Les Alkylbenzenes: Diastéréomerie Des Dérivés Bibenzyles (
Authors: Gouverneur P. J. L. , Mulangala J. Mukinayi 
Published: September 2010

AbstractMeso and racemic bibenzyles are formed by action of di‐t.butyl‐peroxide on alkylbenzenes (ethyl‐, n.propyl‐, n.butyl‐, n.pentyl‐, n.hexyl‐, isobutyl‐, sec.butyl‐, isopentylbenzene) and on para‐X substituted ethylbenzenes (X = F, Cl, Br, CH3, CH3O). The nature of the products is confirmed by decomposition of the corresponding azo compounds and their configuration is determined unambiguously by X‐rays analysis. The differences between meso and racemic dimers are analyzed with regard to their melting temperatures, chromatographic retention times, IR,1H‐NMR and13C‐NMR spectroscopies. The diastereoisomerism of the azo‐bis‐alpha phenylalkanes is also discussed.
Self‐Association of Pyridine in Water
Authors: Huyskens Pierre L. , Smets Roger S. , Mas Dany H. 
Published: September 2010

AbstractThe distribution coefficient P ≡ Fo/Fw of pyridine between cyclohexane and water decreases when the formal concentration Fw in the aqueous phase increases. This can be explained by the self‐association of the pyridine molecules in water. The data are consistent with a Mecke‐Kempter model of self‐association, the constant kMw for the successive additions being of the order of 0.38 ± 0.05 l mole−1. The forces responsible for this self‐association seem to be mainly π … π interactions between the π‐electrons of the aromatic rings of two neighbouring molecules.
Acid Dissociation Constants of Some Thiooxamides and Dithiooxamides
Authors: Aarts A. J. , Herman M. A. 
Published: September 2010

AbstractThe acid dissociation constants of dithiooxamide, methyl‐ and N, N‐dimethyl‐dithiooxamide, No‐methyl‐ and No, No‐dimethylthiooxamide were determined spectrophotometrically. The pKa values (at I = 1) of thioacetamide, thiobenzamide, potassium thiooxamidate and N, N′ ‐dimethyldithiooxamide were determined for comparison. Also H‐D exchange rates were measured for some compounds. The results are discussed taking into account inductive effects, conjugation and hydrogen bonding.
Influence De La Concentration Sur Le Déclin Des Penta‐1, 3‐Dienes Photoexcités à 228.8 nm: Mise En Évidence D'Un Excimère
Authors: Vanderlinden P. , Boué S. 
Published: September 2010

AbstractIn contrast to the results obtained at 253.7 nm, the photolysis of penta‐1,3‐dienes at 228.8 nm in solution displays a strong remarkable concentration dependence.Hence ϕcis → trans increases and ϕtrans → cis decreases with an increasing diene concentration and both figures reach a plateau at ∼1M. A kinetic treatment is presented, which involves dynamic and static quenching (according to Perrin's law) and accounts for experimental data; the scheme consistently suggests that an excimer comes into play in this system.
Stereochemical Studies on Medicinal Agents. 24 Correlation of the Solid‐State Conformations of 4‐Phenylpiperidine Analgetic With the Torsional Relationship Between the Phenyl Group and Piperidine Ring in Solution, a Circular Dichroism Study
Authors: Poupaert Jacques H. , Portoghese Philip S. 
Published: September 2010

AbstractA CD study of 8 representatives of 4‐phenylpiperidine analgetics is presented to correlate their solid‐state conformations with their chiroptical properties in solution. In addition to the benzenoid 1Lb fingerprint, the studied compounds exhibit two waves: the former band around 230‐223 nm is assigned to a 1La transition; the origin of the latter band is not determined. A quadrant rule is tentatively proposed to explain the sign of the 1La Cotton effect.
Nouveaux Derivés De L‚Aryl‐1 Pyridothiazine Et De L‚Arylamino‐8 Pyridothiazolium
Authors: Jamoulle J. C. , Lapière C. L. 
Published: September 2010

AbstractThe synthesis of new derivatives of pyridothiazine and pyridothiazolium is reported. The study of these compounds by RM1H spectrometry has made possible their identification and differentiation.
Synthèse Et Isomérie De Thiométhylpyrazoles
Authors: Maquestiau A. , van Haverbeke Y. , Vanovervelt J.‐C. 
Published: September 2010

AbstractThe shortly performed thermal conversion of 1, 2‐dimethylpyrazolin‐5‐thiones leads to 1‐methyl‐3‐methylthiopyrazoles. The isomerization of these compounds into mixtures of 3‐methylthio and 5‐methylthiopyrazoles is observed after several months at room temperature or more rapidly after prolonged heating. 1‐methyl‐3‐methylthio‐ and 5‐methylthiopyrazoles appear thus respectively as the kinetic and thermodynamic products of the reaction which proceeds at least mainly via an intermolecular mechanism.The thermal intermolecular conversion of 1‐phenyl‐2‐methylpyrazolin‐5‐thiones leads exclusively to 1‐phenyl‐5‐methylthiopyrazoles as described in the literature.
Use of Meldrum's Acids in the Semi‐Synthesis of α‐Carboxylated Penicillins and Cephalosporins
Authors: Crooy P. , De Neys R. , Eliaers J. , Liveyns R. , Simonet G. , Vandevelde J. 
Published: September 2010

Abstractα‐Carboxylated penicillins (i.e. Carbenicillin, Ticarcillin) and cephalosporins are obtained in two steps from the appropriate Meldrum's acid.
Étude structurale de cations générés par ionisation chimique de C‐aminotriazoles.
Authors: Maquestiau A. , van Haverbeke Y. , Flammang R. , De Meyer C. 
Published: September 2010

AbstractMass‐analyzed ion kinetic energy spectra of chemically ionized aminotriazoles were used to obtain structural features of protonated molecular ions, differenciation of isomers giving nearly identical c.i. mass spectra and relative basicities of tautomers in the gas phase. Unimolecular fragmentations suggest that the “ethylated dimers” are formed by ethylation with [C2H5]+ followed by solvation of this collision complex with a second molecule.
Chemical studies of marine invertebrates. XXXI(1). Crassolide, a highly oxygenated diterpene from the soft coral lobophytum crassum. (Coelenterata, Octocorallia, Alcyonacea).
Authors: Tursch B. , Braekman J. C. , Daloze D. , Dedeurwaerder H. , Karlsson R. 
Published: September 2010

AbstractThe complete structure determination of crassolide, a new cembranolide diterpene isolated from the soft coral Lobophytum crassum, is described.
Potentiometric studies of some bivalent metal ion complexes of N‐p‐tolyl‐p‐methoxybenzohydroxamic acid (p‐T‐p‐MBHA)
Authors: Agrawal Y. K. 
Published: September 2010

AbstractThe complexes of N‐p‐tolyl‐p‐methoxybenzo hydroxamic acid with Cu(II), Zn(II), Ni(II) and Mn(II) are studied by potentiometric titration in the mixtures 50, 60 and 70 vol % dioxane and respectively 50, 40 and 30 vol % water at 25 and 35°C · 0.1°C. The thermodynamic ionisation constants of p‐T‐p‐MBHA are reported in the mixtures 10, 20, 30, 40, 45, 50, 60 and 70 vol % dioxane and respectively 90, 80, 70, 60, 55, 50, 40 and 30 vol % water. The order of stability of the complexes and the effect of solvent on the formation constant are discussed.
Complexes of tertiary thioamides. part IV. complexes of N‐dimethylcyanothioformamide, N‐dimethylethylthiooxamidate and NS, NS‐dimethylthiooxamide with pd(II) and Hg(II).
Authors: Aarts A. J. , Desseyn H. O. , Herman M. A. 
Published: September 2010

AbstractComplexes of N‐dimethylcyanothioformamide (DMCTF), N‐dimethylethylthiooxamidate (DMETO) and NS, NS‐dimethylthiooxamide (SDMTO) with Pd(II) and Hg(II) have been prepared, characterized by metal analyses and conductivity measurements, and investigated by vibrational and electronic spectroscopy. The ligands all act as monodentate sulphur donors. With Pd(II) square planar compounds are formed: cis‐Pd(DMCTF)2Cl2, trans‐Pd(DMETO)2Cl2, (LSDMTO), and PdL4(C104)2 (LDMCTF, DMETO, DSMTO). DMCTF and SDMTO form mononuclear tetrahedral compounds (HgL2Cl2) with Hg(II), while DMETO forms a polynuclear compound ([HgL2Cl2]n) with an indefinite structure.
Étude de la conformation et de la tautomérie des azidoazoles par dipolemétrie
Authors: Fayet J. P. , Vertut M. C. , Mauret P. , Claramunt R. M. , Elguero J. , Alcalde E. 
Published: September 2010

AbstractThe experimental and vectorially calculated electric dipole moments of six azidoazoles (imidazole, benzimidazole, pyrazole, indazole, s‐triazole and v‐triazole) have been compared and one preferred conformation of the azido group with respect to the heterocyclic ring has been proposed.
Deoxypolynucleotides‐purification of trinucleotide blocks by solvent extraction
Authors: Kohli Vipin , Kumar Ashok 
Published: September 2010

AbstractTwo protected trinucleotide blocks MMTr‐TpTpT and d‐MMTr‐ABzpTpGi‐Bu were synthesized using phosphodiester approach. The purification of these blocks was achieved in satisfactory yields simply by extraction into a binary organic solvent.
Thermal lactonization of brominated alkylidenemalonates: Synthesis of 2‐buten‐4‐olides
Authors: Verhé Roland , De Kimpe Norbert , De Buyck Laurent , Courtheyn Dirk , Schamp Niceas 
Published: September 2010

AbstractHeating of dialkyl 2‐bromoalkylidenemalonates in boiling xylene resulted in lactonization with formation of 2‐alkoxycarbonyl‐2‐buten‐4‐olides. Bromination of dimethyl 2‐phenylpropylidenemalonate with NBS in CCI4 gave the corresponding butenolide. However, heating of the 2‐bromocyclohexylidenemalonate only afforded the dehydrobromination product.
Electrocatalytic reduction of butanone I. oscillating accumulation of intermediates
Authors: Feyaerts K. , De Hemptinne X. 
Published: September 2010

AbstractButanone is reduced to butane and butanol‐2 on Pt in H2SO4 electrolyte. Oscillating accumulation of intermediates in the butane reaction is observed. Their chemical nature is discussed: a chemisorbed butyl radical and interstitial hydrogen atoms.
Nitrogen‐14 indor spectra of some 2‐substituted pyrimidines
Authors: McFarlane William , Turner Christopher J. 
Published: September 2010

Abstract14N chemical shifts have been measured for eleven 2‐substituted pyrimidines using a 1H ‐ {14N} double resonance technique in conjunction with spectral accumulation. Correlations are noted between the 14N chemical shifts and calculated π‐electron densities at nitrogen.
Trapping of thiaziridinimines with N‐sulfinylamines
Authors: L'abbé Gerrit , van Asch Alex , Declercq Jean Paul , Germain Gabriel , van Meerssche Maurice 
Published: September 2010

AbstractThe reactions of 4‐alkyl‐5‐arylsulfonylimino‐1,2,3,4‐thiatriazolines with N‐sulfinylamines at 60‐70° yield 3‐oxo‐5‐arylsulfonylimino‐1,34,2,4‐dithiadiazolidines 4 which are smoothly converted by hydrolysis into S‐aminoisothio‐ureas 5. In contrast, the acetyl derivative 4g hydrolyzes into thiadiazoline 7. Structure assignment of the products was based on spectral and combustion analyses, chemical reactions, and, in the case of 4e, on an X‐ray structure determination.
Cyclopentanones Stereochemistry of the Lithium‐Liquid Ammonia Reduction of 2, 3‐Dialkyl‐5‐Hydroxy‐2‐Cyclopentenones
Authors: Hanselaer René , Samson Marc , Vandewalle Maurits 
Published: September 2010

AbstractThe stereochemistry of the lithium‐liquid ammonia reduction of 2, 3‐dimethyl‐5‐hydroxy‐2‐cyclopentenone (1) and 3‐t.butyl‐2‐methyl‐5‐hydroxy‐2‐cyclopentenone (2) is studied in function of a set of proton donors. A high degree of stereoselectivity is observed as practically only two (predominantly one isomer) out of the eight diastereoisomeric 3, 4‐dialkyl‐1, 2‐cyclopentane diols 3 or 4 are formed.
The Crystal Structure of Monoclinic Copper(II)‐hydrogen‐(1)‐Malate Dihydrate
Authors: van Havere W. , Lenstra A. T. H. 
Published: September 2010

AbstractCopper(II)‐hydrogen‐(1)‐malate crystallises in the monoclinic space group P1. Characteristics of the unit cell are: a=7.589 Å, b=8.158 Å, c=10.210 Å, γ=87.28° and Z=2, with chemical composition Cu(C4O5H5)2.2H2O.The Cu2+ ion is coordinated by six oxygen atoms, all originating from the hydrogen malate ions. Two Cu‐O distances are elongated due to the Jahn‐Teller effect.The two crystallographically independent malate ions have significantly different geometries.
Solution Conformation of Lonomycin Free Acid and Lonomycin Sodium Salt. An 1H‐NMR Study
Authors: Rodios Nestor A. , Anteunis Marc J. O. 
Published: September 2010

AbstractThe conformations and relative configurations of the antibiotic Lonomycin free acid and its sodium salt have been revealed in a high resolution 1H‐nmr study in non polar solvents. The basic chair forms of the three pyranoïd rings have been confirmed although deformations are noted for ring B, heavily substituted and possessing syndiaxial strain. The fixed rotarmeric states around the acyclic fragments do not change by passing from the free to the complexed form. The extracted data suggest that the molecule possesses a rigid frame work forming a pseudocyclic backbone with a haid‐to‐tail buttoning shut by a hydrogen bond.
Métallation Des Halogènures D'Aryle Par le Tributylstannyllithium Dans le HMPT
Authors: Quintard Jean‐Paul , Hauvette‐Frey Sabine , Pereyre Michel 
Published: September 2010

AbstractTributylstannyllithium was prepared in the absence of metallic lithium by cleavage of hexabutylditin with butyllithium in HMPA. It reacts with bromotoluenes in a completely regiospecific way. However parachloro and fluorotoluenes give mixtures of tin substituted compounds whose compositions strongly depend on the experimental conditions and on the nature of the halogen. All data are in agreement with a competition between anionic and radical mechanisms. Product analysis was realised by means of gas chromatography, NMR Spectroscopy (13C and 119Sn) and mass‐spectrometry.
Studies on organophosphorus compounds XXVI. Synthesis and 13C NMR spectra of N,N‐dialkyl thioamides
Authors: Fritz H. , Hug P. , Sauter H. , Winkler T. , Lawesson S. ‐O. , Pedersen B. S. , Scheibye S. , Logemann E. 
Published: September 2010

AbstractBy a new thiation reagent,1, 4, 11 the dimer of p‐methoxyphenylthionophosphine sulfide, 3, a series of thioamides have been prepared in almost quantitative yields from the corresponding amides, Carbon‐13 NMR spectra of tertiary thioamides of formic, acetic, trifluoroacetic, propionic and butyric acids have been completely assigned with the aid of extensive double resonance and shift reagent experiments and the data obtained have been compared with those of the analogous amides.8 Also a linear relation between the 13C chemical shifts of CS of the thioamides and CO of the corresponding amides has been found by a least square linear regression analysis: δ(CS) = 1.60° (CO)−72.3.
Imine chemistry I. A new route to pyrroles and related compounds from imines and 2‐chloroacrylonitrile
Authors: Olesen S. O. , Madsen J. Ø. , Lawesson S. ‐O. 
Published: September 2010

AbstractThe Michael addition of 2‐chloroacrylonitrile to imines (potential enamines) and the subsequent elimination of HCN produced pyrroles and condensed pyrroles.
The raman spectrum of pyridines in charge transfer complexes with bromine
Authors: Maes G. 
Published: September 2010

AbstractRaman spectra of several pyridine derivatives (substituent = CH3‐, tC4H9‐, Cl‐, Br‐, I‐) complexed with bromine are studied in CH2Cl2 and in CH3CN. Marked changes in frequency, intensity and degree of depolarization of the Raman bands of pyridines are observed. These spectral perturbations seem to depend on the position of the substituent and are further discussed in terms of the charge transfer theory.
AN 1H‐NMR study of the polyether antibiotic etheromycin‐Na+ (CP‐38 295‐Na+).
Authors: Anteunis Marc J. O. , Rodios Nestor A. 
Published: September 2010

AbstractThe structure and the solute conformation in nonpolar solvents of the title compound have been revealed by high resolution 1H‐nmr spectroscopy. The ionophore possesses the typical pseudocyclic conformation of the polyether antibiotics by which the head and tail is held together through H‐bond binding, sequestering the cation from the lipophilic surrounding. The extra sugar like moiety (ring G,) seems not to participate in cation coordination.
N‐Acylamino acids and peptides VI. A Simple synthesis of N‐acylglycines of the benzoyl‐ and cinnamyl type
Authors: Brussel W. Van , van Sumere C. F. 
Published: September 2010

AbstractA very simple and fast method for the synthesis of N‐acylamino acids and peptides from the benzoyl‐ and cinnamyl type is described. The method is based on the use of N‐hydroxysuccinimide as reagent (active ester method).The characteristics and chromatographic parameters of some new benzoylglycines are given.
The Determination of the Rare Earth Elements in Rocks by Spark Source Mass Spectrometry
Authors: van Puymbroeck J. , Gijbels R. 
Published: September 2010

AbstractThe determination of the rare earth elements in rocks by high frequency spark source mass spectrometry, using photoplate detection, was investigated.Several standard rocks (BCR‐1, JB‐1, JG‐1, NIM‐G, NIM‐N) were analysed by the “direct” method, and after three different selected enrichment procedures: peroxide fusion and successive hydroxide and fluoride precipitations; acid digestion and cation exchange chromatography; acid digestion and mixed‐solvent anion exchange chromatography. These preconcentration methods are discussed and the results obtained are compared with each other.A mixed‐solvent anion exchange procedure permits to determine all rare earth elements with a precision of 10%.
Ionisation Constants of N‐Arylhydroxamic Acids
Authors: Agrawal Yadvendra K. 
Published: September 2010

AbstractThe ionisation constants of N‐0‐tolyl‐p‐substituted benzohydroxamic acids have been determined in 10‐70% v/v dioxane‐water media at 25 and 35±0.1°C. The pKa's in aqueous media (at 10% dioxane) have been obtained using the method of extrapolation and least squares. The pKa values vary linearly with the mole fraction of dioxane. These constants are tested for the applicability of the Hammett equation.
A Potentiometric Determination of the Self‐Association Constants of Some L‐Amino Acids in Aqueous Solution
Authors: Vliegen J. , van Poucke L. C. 
Published: September 2010

AbstractBecause of its biochemical interest the self‐association behaviour of six natural occuring L‐amino acids was studied by potentiometry in aqueous solutions of 3M KCl.The investigated amino acids were glycine, L‐alanine, L‐proline, L‐hydroxyproline, L‐serine and L‐threonine.The experimental results are obtained in two different ways: in a first treatment of the experimental data only association, in a second treatment association and variation of the Eo of the cell are taken into account.The following conclusions can be made: in both treatments only dimeric species are found of which those of L‐serine are the most stable, for all amino‐acids H3L2+ is detected and seems to be more stable than the other dimeric species.
Contribution to the Complex‐Formation of Diphenylcarbazone with cations. Complexes of Zinc, Nickel, and Cobalt
Authors: Peeters O. M. , Blaton N. M. , Willems G. J. , De Ranter C. J. 
Published: September 2010

AbstractThe complexes of diphenylcarbazone with zinc, nickel and cobalt are studied spectrophotometrically in a 50 volume percent aqueous acetone medium. The wavelength of maximal absorbance is situated between 520‐525 nm. The three complexes show a 1:2 stoichiometry as derived independently from the method of continuous variation and the slope‐ratio method. The molar absorptivities amount to 70000‐77500 1 mo1−1 cm−1 and the conditional constants have an order of magnitude of 107.
Photogalvanic Cells. 5. Oxidation Photocurrents of Triphenylmethane Dyes at the SnO2 Bubbling Gas Electrode
Authors: Kirsch‐De Mesmaeker A. , Kanicki J. , Leempoel P. , Nasielski J. 
Published: September 2010

AbstractThe photoelectrochemistry of Crystal Violet, Methyl Violet and Malachite Green in the presence of hydroquinone is examined at the SnO2 bubbling gas electrode. For the first two dyes, the Stern‐Volmer constants of the process responsible for the supersensitization, determined by the previously described (1) electrochemical method, could correspond to the quenching either of the oxidized dye or of the excited triplet state.An interesting new feature emerges from the study of the Malachite Green‐hydroquinone system: two species seem to be involved in the supersensitization process having rather different lifetimes, and thus quenched in different hydroquinone concentration ranges.
Studies for an Alternative Synthesis of 11‐Desoxy‐10‐Hydroxy Prostaglandin Analogs
Authors: Bracke Pieter‐Paul , Verzele Frank , Wyffels Wilfried , Vandewalle Maurits 
Published: September 2010

Abstract3‐(Carboxymethyl)‐1,2,4‐cyclopentanetrione prepared from laevulinic acid and diethyl oxalate is an excellent starting material for a high yield and stereo‐selective synthesis of 11‐desoxy‐10‐hydroxy‐prostaglandin F2α. On the other hand 3‐(2'‐benzyloxyethyl)‐1,2,4‐cyclopentanetrione a precursor, also in theory suitable for 12‐methyl substituted analogs, gives less satisfactory results because of lack of stereochemical control.