Stereochemical Changes Research Articles

Structures of the sulphones formed in the oxidation of the products of thiol addition to chloronorbornadienes and related compounds

The sulphides formed by the respective additions of ethanethiol and benzenethiol to some chloronobornadienes are converted into the corresponding sulphones without change in stereochemistry. The only exceptions are the oxidation, with hydrogen peroxide in acetic acid, of 1,4,5,6,7,7-hexachloronorborn-5-en-2-endo-yl phenyl sulphide to afford the 2-exo phenyl sulphone, and of 1,2,3,5-endo,6,6-hexachloronoborn-2-en-7-syn-yl phenyl sulphide to give an epimeric mixture of the corresponding 7-syn and 7-anti phenyl sulphones. Product sulphones have been treated with potassium t-butoxide in t-butyl alcohol in an effort to effect epimerisation, and to provide evidence about the thermodynamic stability of individual sulphones. It is probable that in the presence of potassium t-butoxide in t-butyl alcohol, many of the derived carbanions have complete configurational stability, and hence the sulphones are not epimerised.

Mechanisms and steric course of octahedral aquation. XIV. Activation parameters and steric course of aquation of trans-chloro- and trans-bromoazidobis(ethylenediamine)cobalt(III) cations

The rates and steric course of aquation of $_t_r_a_n_s-[Co(en)_2N_3Cl]ClO_4$ have been reexamined over a 50° range of temperature. At 25.0°, $[H^+]=0.01M,_k=2.6*10^-^4_s_e_c^-^1,\Delta H =20.7 \pm 0.3 kcal/mol, and \Delta S= -6 \pm 2 eu. $ The corresponding bromo complex has been prepared and examined for the first time. At 25.0°, $[H^+]=0.01 M,_k=8.5*10^-^4_s_e_c^-^1, \Delta H = 20.0 \pm 0.5 kcal/mol, \Delta S= -6 \pm 2 eu.$ In all cases, after correction for subsequent isomerization, it is shown that aquation occurs with complete retention of configuration. The specific rate of approach to equilibrium of $ _c_i_s- and _t_r_a_n_s- Co(en)_2N_3OH^2^+ $ was also measured over a 30° temperature range. At 25.0°, $[H^+]=0.010 M,_k=9.6 * 10^-^5 _s_e_c^1-^1, \Delta H= 32.0 \pm 0.5 kcal/mol, \Delta S= +30 \pm 3eu.$ The equilibrium composition (43% $_t_r_a_n_s$) is independent of temperature over this range. The steric course of spontaneous and $H_g^2^+$ -catalyzed aquation of $_c_i_s-Co(en)_2N_3Cl_+$ has also been rexamined. It has been shown conclusively that both process give identical amounts of the $_c_i_s-$ and $_t_r_a_n_s-$aquoazido products and there is reasonable evidence to suggest that some 15% of the intial reaction product has the $_t_r_a_n_s$ configuration- This is the first example of stereochemical change in the spontaneous aquation of a $_c_i_s-Co(en)_2AX^n^+$complex.

Re: Stereochemical changes during octahedral substitution reactions

Re: Stereochemical changes during octahedral substitution reactions

Preparation and properties of metal complexes with 6-methyl-2-aminomethylpyridine—II: Four-, five-, and six-co-ordinated cobalt(II) complexes[1

The preparation and properties of eight new complexes Co(mepic) 2 X 2. nH 2O (mepic = 6-methyl-2-aminomethylpyridine; X = Cl, Br, NCS, NO 3, and ClO 4; n = 0–2·5 and Co(mepic) 2 XClO 4 ( X = Cl, Br, and I) are reported. Magnetic susceptibility measurement hows that all of them have high-spin configuration corresponding to three unpaired electrons. The solid diffuse reflectance spectra and the i.r. spectra reveal that in the solid state Co(mepic) 2(ClO 4) 2 is a four-co-ordinated tetrahedral complex, whereas Co(mepic) 2 XClO 4 are five-co-ordinated complexes which have pseudotrigonal-bipyramidal configuration. On the other hand, four complexes Co(mepic) 2 X 2. nH 2O ( X = Cl, Br, NCS, and NO 3) are six-co-ordinate; the surroundings of the cobalt ions are discussed. In the aqueous solutions, all of them exhibit the same electronic spectra, showing that the solvolysis and the stereochemical changes leading to the same product occur. The main species thus formed in the aqueous solutions seems to be a six-co-ordinated complex [Co(mepic) 2(H 2O) 2] 2+. In the nitromethane solutions, however, the situation is quite different here; the absorption spectra of Co(mepic) 2(NO 3) 2 and Co(mepic) 2(ClO 4) 2 are nearly identical with those of the solid reflectance spectra; the former is octahedral and the latter is tetrahedral in this solvent. It is shown that the complexes [Co(mepic) 2 X]ClO 4 seem to disproportionate in part in nitromethane solution into tetrahedral [Co mepic X 2] and octahedral [Co(mepic) 3] 2+. The stereochemistry of all the complexes is discussed.

Stereochemical changes during octahedral substitution reactions

Stereochemical changes during octahedral substitution reactions

Ipecacuanha alkaloids. 8. Chemical correlation of the indole and ipecacuanha alkaloids.

(–)-3,4-Diethylcyclopentanone is prepared and converted by steps not involving the asymmetric centres into the salts (25) and (27), the enantiomers of which have been derived without stereochemical change from protoemetine (3) and corynantheine (14), respectively. These experiments constitute a chemical correlation of the indole and Ipecauanha groups of alkaloids. It is thus confirmed that emetine (1) and corynantheine (14) have the same absolute configuration. The biosynthetic aspects are discussed. Preliminary work involving lactams, e.g.(7), derived from benzoquinolizidines is briefly described.

Substitution reactions of metal complexes

Abstract

Carbon monoxide insertion reactions V. The carbonylation of methylmanganese pentacarbonyl with 13CO

The reaction of CH 3Mn(CO) 5 with 13CO and the decarbonylation of CH 3 13COMn(CO) 5 have been investigated by infrared spectroscopy. The results previously obtained by Coffield and coworkers with 14CO have been confirmed. Furthermore, by use of 13CO the stereochemical changes occurring during the carbonylation reaction have been studied. The results are in agreement with a mechanism of methyl migration for the conversion of methyl manganese pentacarbonyl into acetyl manganese pentacarbonyl by carbon monoxide.

Stereochemical Relationships between Epithio, Halomercapto and Hydroxymercapto Derivatives of Oleic and Elaidic Acids

AbstractInversion takes place both on opening and restoring an epithio ring, and likewise when halomercaptooctadecanoic acids are derived from hydroxymercaptostearic acids. No change in configuration occurs when an epoxy acid is converted into an epithio acid. A cis epoxy fatty acid can be converted into a trans epoxy acid via the hydroxymercapto and halomercapto‐octadecanoic acids. These stereochemical changes conform to Walden inversion and double bond addition reactions. The stereochemical behaviour of the sulphur compounds closely resembles that of their oxygen analogues.

Relationship of structure to fungitoxicity of cycloheximide and related glutarimide derivatives

The effect on biological activity of various group substitutions and stereo-chemical changes in the l-cycloheximide molecule was studied. Compounds were assayed for toxicity to cells of Saccharomyces pastorianus and to a cell-free protein-synthesizing system from this organism. Substitution of the imide hydrogen with a methyl group, esterification of the hydroxyl group with acetate, or conversion of the ketone to an oxime, semicarbazone, or hydroxyl group resulted in greatly diminished or complete loss of activity Stereoisomers which differed from l-cycloheximide in configuration of the trisubstituted cyclohexanone ring were low in activity. An isomer with the same cyclohexanone ring configuration as l-cycloheximide, but with a different orientation of the methyl group at the 4-position, was half as active as l-cycloheximide. A cyclic ketone was not an absolute requirement for biological activity of glutarimide antibiotics because streptimidone which contains an aliphatic ketone was about 30 per cent as active as l-cycloheximide. The principal steric requirement in the cyclic ketone moiety appears to be proper orientation of the carbonyl group in respect to the remainder of the molecule. Substitution data suggest that the keto, hydroxyl, and imide nitrogen groups may be involved in a 3-point attachment of the glutarimide antibiotics to the substrate. Acetoxycycloheximide and streptovitacin-A were less toxic to cells but more toxic to the cell-free protein-synthesizing system than was cycloheximide. No glutarimide derivatives were active against whole cells or a cell-free protein-synthesizing system of the cycloheximide-resistant yeast, S. fragilis.

Rotatory Dispersion and Configuration of Cobalt(III) Complexes

The rotatory dispersion curves of 30 cobalt(III) complexes have been described and the absolute configurations of some of the complexes have been assessed by relating their rotatory dispersion curves to that of the D(+)-[Coen3]3+ ion. The assessment is supported by recent kinetic and stereochemical results. The use of rotatory dispersion to detect stereochemical change is discussed.

The Butyllithium-Initiated Polymerization of 1,3-Butadiene

Abstract The organolithium polymerization of isoprene (2-methyl-1,3-butadiene) has been studied in some detail. Hsieh and Tobolsky have reported that the polymer prepared in benzene or heptane had more than 90% cis-1,4-structure. Polyisoprenes prepared in ethers showed a change in stereochemistry to 3,4-, 1,2-, and trans-1,4-microstructures. Other research further studied the sensitivity of polymer stereochemistry to solvent and the specific organometallic initiator. Although it was observed long ago that organolithium compounds cause the polymerization of butadiene, the stereochemistry of the polymer has been reported much less completely. The patent literature contains references in this area, and Russian researchers have studied the butyllithium-initiated polymerization of butadiene in the presence of ethers, oxygen, alcohols, and thio ethers. This communication describes the polymerization of butadiene by butyllithium in n-heptane; it discusses the stereochemistry of the polymer obtained and the effect of catalyst and monomer concentration, polymerization temperature, and the presence of ethers on the details of polymer structure. The results obtained are compared with the reported data for the alkyllithium-initiated polymerization of isoprene.

Precursors of Coprosterol and the Bile Acids in the Animal Organism

THE transformation of cholesterol into coprosterol in its passage through the body involves a reduction of the C5:C6 double bond, and a transition from the allocholanic—to the cholanic-ring system. Although it is established that the bacterial flora of the intestine is concerned in the reduction process, the mechanism by which the stereochemical change is brought about is unknown. A clue was afforded by a study of the properties of cholestene—3:4—diol, a primary oxidation product which is formed under various conditions of mild oxidation from cholesterol, and is also a constituent of the resinous product called oxycholesterol1. Being an glycol, this substance easily rearranges by loss of water into the corresponding ketone, that is, cholestenone. Since cholestenone (= coprostenone) yields coprostanone on reduction, which in turn is reducible to coprosterol (= coprostanol) and epi-coprosterol2,3, we formed the working hypothesis that the reactive primary oxidation product, cholestene-diol, may play a role in cholesterol metabolism, giving rise to the formation of cholestenone as an intermediary product. On this assumption, cholestenone and coprostanone, and not cholesterol itself, are the immediate precursors of coprosterol which is formed from them in the intestine by bacterial reduction. Further, an explanation is afforded for the origin of the epi-hydroxycholane system in lithocholic acid (and the other bile acids?)4, which may be derived from epi-coprosterol by oxidative cleavage of the side chain with loss of acetone.