The decomposition of sulphonyl-hydrazone salts—I Mechanism and stereochemistry

The rate-determining stage in the Bamford-Stevens reaction is shown to be a unimolecular elimination from the anion of the sulphonylhydrazone. This gives, apparently in all cases, a secondary aliphatic diazo-compound, which then undergoes thermal decomposition. Such diazo-compounds may decompose in solvents rich in available protons, such as were originally used by Bamford and Stevens, mainly via the diazonium cation, and the reaction then degenerates into a variant of the normal deamination reaction. Acetamide is a convenient solvent for minimizing this effect, and gives higher yields of hydrocarbon products.     

Studies on the stereochemistry of 1,2,6-trimethyl-4-piperidone

In the effort to create new derivatives of analgesically active spiropiperidines intermediate 1,2,6-trimethyl-4-piperidone was synthesized. The substitution of the skeleton gives rise to configurational as well as conformational isomerism. Despite the symmetry of 1,2,6-trimethyl-4-piperidone two different sets of signals were present in the ¹H and ¹³C NMR spectra. They were supposed to arise from a cis/trans mixture of 1,2,6-trimethyl-4-piperidone. In contrast to this explanation only two signals of the methyl groups and hydrogens at carbon atoms 2 and 6 were observed in the ¹H and ¹³C NMR spectra, normally expecting one for the cis- and two for the trans-isomer. To solve this discrepancy, the kind of isomeric mixture of 1,2,6-trimethyl-4-piperidone leading to the ¹H and ¹³C NMR spectra was examined. Energy differences between chair conformations of both the cis- and the trans-isomer of 1,2,6-trimethyl-4-piperidone and the potential energy surface of the equilibration process of the trans-isomer of 1,2,6-trimethyl-4-piperidone between its chair conformers were determined by quantum chemical calculations. The barrier height of the equilibration process was measured by high and low temperature NMR measurements to confirm the theoretical outcome. The results of all investigations agree nicely and proved a cis-/trans-mixture of 1,2,6-trimethyl-4-piperidone being present at room temperature.     

Curamycin—I Isolation and characterization of some hydrolysis products

From cultures of Streptomyces cura-coi, a chlorine containing glycosidic antibiotic, named curamycin, has been isolated. Curamycin on acid hydrolysis yields a crystalline product, curacin, and a mixture of monosaccharides. Curacin, which contains all of the chlorine of curamycin, is the ester of dichloroisoeverninic acid (3,5-dichloro-4-hydroxy-6-methoxy-2-methyl-benzoic acid) with a di-desoxyaldose C₆H₁₂O₄, whose structure has not as yet been established. Three other monosaccharides are present, two of which could be identified as -lyxose and 4-O-methyl- -fucose.     

Alkyl-oxygen heterolysis in 4-aryl and 4-heteroaryl-4-piperidinols and esters

Acetoxy and propionoxy esters of 1-phenethyl-4-(2′-furyl)-4-piperidinol hydrochlorides, upon treatment with one mole excess of hydrogen chloride in an alkanol, were converted into corresponding 4-alkoxy ethers and elimination products. These results are interpreted in terms of reactions of carbonium ions, produced from the esters by alkyl-oxygen heterolysis. Factors affecting carbonium ion generation and fate have been studied and include the electronic character of the 4-aryl substituent, nature and size of the nucleophile, degree of acidity and role of the piperidine nitrogen atom.     

Aspects of stereochemistry—I Properties and reactions of some diols

The extent of intramolecular hydrogen-bonding, as determined by infra-red spectroscopy in the hydroxyl stretching region, in certain vicinal diols of cyclohexane, cyclopentane, tetrahydropyran and tetrahydrofuran and in related compounds provides evidence for the stabilities of different conformations. In certain compounds these stabilities can be affected by hydrogen bonding from a substituent hydroxyl group to a ring oxygen. Additional evidence is provided in the case of the tetrahydropyran diols by [M]_D values. The rate of reaction of the vicinal diols of these cyclic systems with glycol splitting reagents, and their zone electrophoretic mobility in an alkaline borate buffer is influenced by the presence of a ring oxygen.     

Synthesis and reactions of some 4-heteroaryl-3-nitrocoumarins—

By the action of 2-aminothiazole, 2-aminopyridines, and 2-aminopyrimidines, respectively, on 4-chloro-3-nitrocoumarin ( 3 ) the corresponding 4-heteroarylamino-3-nitrocoumarins 5–7 have been isolated in very good yields. Reactions of coumarins 6 and 7 with either aqueous tetrabutylammonium bisulfate/sodium hydroxide in a two phase system or 5% aqueous sodium hydroxide have been studied.     

Translational energy release and stereochemistry of steroids 4—Epimeric 3-keto and 3-hydroxy steroids

The translational energy, T, released during CH₃˙ loss from the molecular ions of epimeric steroid ketones and from both molecular and [M-H₂O]⁺˙ ions of epimeric alcohols of the androstane, pregnane and cholestane series, differing in the mode of the A/B ring junction, has been measured. These data provide a simple and rapid method for identifying the configuration of the epimeric centres. Of the compounds studied, it is found in 3-hydroxy steroids that the 5β-isomers release the smaller amounts of translational energy for CH₃˙ loss. In most of the 3-keto steroids investigated, the opposite is found, i.e. the larger T values are observed for the 5β-isomers. Exceptions occur when further keto groups are introduced at the 11- or 17-positions. A small range of epimeric pairs of 17-hydroxy, 17-keto and 4-keto steroids have also been studied, the 5β-isomer giving the lower T value in each case. The importance of hydroxy and keto groups at the various sites within the steroid structure in determining the T values is discussed.     

Mass spectrometry of onium salts—I. Studies on anilinium oxides

The mass spectra of the three isomeric trimethylanilinium oxides and their methyl-d₃ analogues show that the m- and p- isomers undergo intermolecular trans-O-alkylation before evaporation. In the o-isomer, only 10% transalkylated product is observed and there is strong evidence that most of this isomer evaporates without undergoing structural changes. By indirect introduction, however, the o-isomer showed only transalkylated product. The most important fragmentation patterns on electron-impact are α-cleavage on the N-methyl carbon or expulsion of the O-substituent with formation of a quinoid structure. The latter dominates for the o- and p-methyl ethers while the former is the most important pathway for the m-isomer and for the corresponding phenols. Lower fragments are of modest intensity.     

Preparation and stereochemistry of 3-phenacylidenephthalimidines

Yields of 3-phenacylidenephthalimidines are maximized and yields of phthalimide byproducts are minimized by use of acetic acid as the solvent in reactions of amines with 3-phenacylidenephthalides. The 3-phenacylidenephthalimidines are formed as E, Z mixtures, in which the E isomers predominate. A homonuclear NOE nmr experiment was employed to determined product stereochemistry.     

Analogies between silicon and phosphorus stereochemistry—I : Influence of the leaving group on the stereochemistry of nucleophilic displacement at phosphorus

Stereochemistry of cyclic halogenophosphates has been studied by adding aryloxides, in THF. All extra parameters being equal, the fluoro substituent which is of the more electronegative (and the more apicophilic) is displaced with the more predominant retention F>Cl≈Br. Such behaviour cannot be explained with the usual concepts of phosphorus stereochemistry and, in particular, the generally accepted view of apical attack giving the more stable P^V intermediate. By contrast, strong analogies with the stereochemistry observed at silicon are clearly evidenced. Like for silicon compounds, front-side attack could explain predominant retention, particularly in P-F bond cleavage. Trigonal bipyramidal intermediates with the entering group in equatorial position and the leaving group in apical position, or square-pyramidal geometries may be envisaged.     

Studies on lactams—XX Stereochemistry of some penicillin sulfoxides and analogs from lanthanide induced shifts

Lanthanide induced shifts have been shown to provide reliable information on the steric disposition of protons in the vicinity of the sulfoxide group in penicillin derivatives and analogs. Because of its dipolar nature the sulfoxide bond serves as a favored site for complex formation with the lanthanide. The configuration of several penam sulfoxides and the conformation of the thiazolidine ring of one of them have been deduced.     

Bridged ferrocenes—VI Synthesis and stereochemistry of [1,1]ferrocenophanes

Synthetic routes to compounds of the [1.1]ferrocenophane class have been devised making use of fulvene and acid chloride precursors and the parent compound has been prepared by direct synthesis. The bridged ferrocenes obtained by these different approaches have been chemically interrelated and their structure and stereochemistry have been investigated through study of their spectral properties. Sodamide promotes intramolecular cyclisation of 1,1′-bis(-cyclopentadienylideneethyl)ferrocene to a [3]ferrocenophane derivative.     

Studies on spiroborate complexes—I. A new synthesis of bis-catechol spiroborate and its analogs using 2-amino-4-methylpyridine borane

A new synthesis of bis-catechol spiroborate and its analogs are described. Not only five-but also six- and seven-membered spiroborates are obtained. The reaction mechanisms are also discussed.     

Studies directed toward synthesis of guanosine 8,5''-imino cyclonucleosides and derivatives—I

8,5'-Aminimino bridging in the guanosine series using 5'-O-tosyl (1) and 5'-O-mesyl derivatives (2) of 2',3'-O-isopropylidene-8-bromoguanosine (5) and hydrazine gave N³,5'-cyclized product 3 and the N⁵,5'-cyclonucleoside of 4-carboxyhydrazido-5-amino-2-bromoimidazole 4. To exclude the N³,5'-cyclization through ionization in the base moiety, a N²-dimethylaminomethylidene-N¹-methoxymethylene derivative 7 was synthesized from 5 through the N²-protected compound 6. 7 was converted into the N²-dimethylaminomethy analogue 8, which with hydrazine yielded first the N²-deprotected form of 8 (9). 8 or 9 with hydrazine under forcing conditions gave an 8,5'-aminimino-N¹-methox derivative 10. Oxidation of 10 with sodium metaperiodate or sodium nitrite yielded 8,5'-imino-N¹-methoxymethyleneguanosine (11a) and 8,5'-imino-N¹-methoxymethylenexanthosine derivative 11b, respectively. 11a was deprotected to 8,5'-imino-N¹-methoxymethyleneguanosine 12.     

Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems

The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S^- and M represent the initiator and D₄, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k₁ = 2.3 × 10^?4 l./mole-sec., k₂ < 2.3 × 10^?5 sec.^?1, k₃ = 2.75 × 10^?2l./mole-sec. k₄ ≈ 1.17 × 10^?2 sec.^?1, K₁ > 10 l./mole and K₂ ≈ 2.35 l./mole. The rate constants k₁ and k₃ were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K₂, indicating zero ΔH and positive ΔS in the propagation reaction.     

Negative ion mass spectrometry—I: The spectra of some stabilised alkylidenetriphenyl-phosphoranes

The 70 eV negative ion mass spectra of a series of phosphoranes exhibit significant peaks for ions resulting from skeletal rearrangements. The primary fragmentation reactions of the molecular anions, which involve reduction of the phosphorus from the penta- to the ter-valent state, have been rationalised in terms of the relative stabilities of the products formed. The processes occurring are in some cases analogous to and in other cases complementary to, those previously observed in the positive ion spectra of similar compounds.