Dimeric compounds

The validity of the model was demonstrated by reacting 35 under the same reaction conditions as expected, only one diastereoisomer 41 was formed, the structure of which was confirmed by X-ray analysis. When the vinylation was carried out on the isothiazolinone 42 followed by oxidation to 40, the dimeric compound 43 was obtained, showing that the endo-anti transition state is the preferred one. To confirm the result, the vinyl derivative 42 was oxidized and the intermediate 40 trapped in situ with N-phenylmaleimide. The reaction appeared to be completely diastereoselective and a single diastereomer endo-anti 44 was obtained. In addition, calculations modelling the reactivity of the dienes indicated that the stereochemistry of the cycloaddition may be altered by variation of the reaction solvent. 

It is known that Na2Fe(CO)4 can be silylated twice to form cri-[(H3C)3Si]2Fe(CO)4 [109]. Also the reaction of Na2Fe(CO)4 with 1.1-dichlorosilanes has been described and leads exclusively to the dimeric compounds [110, 111], In polar solvents the formation of dimers can be suppressed and monomeric base-stabilized compounds are obtained. A very elegant procedure is the in-situ generation of the carbonylate anions in solution by deprotonation of H2Fe(CO)4. 

Monomeric base adducts of silylene complexes can be transformed into dimeric compounds at elevated temperatures with loss of the donor. This applies also to reactive donor-free compounds. 

Fig. 20. Reaction of 2,6-pyridinedimethanol with arylboronic acids gives the tetrameric macrocycles 74 and 75. Dimeric compounds are known with silicon 76 and 77 and sulfur 78...

Both dimeric and trimeric cycloaikylidine peroxides can be synthesized by treatment of the corresponding cyclic ketones with H2O2 in acid solution. The trimeric peroxide is formed first and is subsequently converted to the dimeric compound. ... 

The pyrethroid insecticides fenvalerate and cypermethrin are hydrolyzed under alkaline conditions at low substrate concentrations, but at higher concentrations the initially formed 3-phenoxybenzaldehyde reacts further with the substrate to form dimeric compounds (Figure 1.22) (Camilleri 1984). 

Mansour, M.A., Connick, W.B., Lachicotte, R.J., Gysling, H.J. and Eisenberg, R. (1998) Linear chain Au(I) dimer compounds as environmental sensors A luminescent switch for the detection of volatile organic... 

Oxidation of aknadinine with silver nitrate gave a pair of dimeric compounds, one of which was identical to the naturally occurring bisaknadinine (8) and the other assumed to be a stereoisomer arising from an axial chirality concerning the mode of biphenyl linkage (21,22). It was impossible, however, to determine from ORD and CD measurements whether the isomer is of natural bisaknadinine (8). Therefore, unambiguous proof of the stereochemistry was achieved, using the X-ray diffraction method, and the... 

Diphenyldisulfide or diphenyldiselenide react with AgAsF6 in liquid S02 to give [Ag2(Ph2E2)4](AsF6)2 (E = S, Se) (222).1294 A dimeric compound has been prepared with the ditelluride, [Ag2 Te2(p-F-C6H4) 2]. 169... 

The X-ray structures are known of a number of ketone ligands, including hexanedione and 4-methylcyclohexanone, that have bound as monodentate ligands in the fifth coordination site of zinc porphyrin complexes.347,348 Oxaphlorin dimeric compounds are also known where the oxygen from a neighboring porphyrin ring coordinates in the fifth coordination site of a neighboring zinc porphyrin unit.349... 

Grignon-Dubois and coworkers have shown that reduction of a quinoline using zinc and acetic acid in THF gives the dimeric compound 3-177 via intermediate 3-176 (Scheme 3.47) [70J. Usually, a mixture of the syn- and anti-products is formed the substituent has some influence on the regioselectivity of the dimerization and cydization step. With R = H and R = 6-Me, only the benzazepine 3-177 were produced, by a head-to-head dimerization. 

The dimeric compound 68 is virtually planar. The angles between the main plane of the imidazole ring and the main plane of the pyndo[2,l-/]tnazinium system are 15.2° and 11.6° in each half of the structure <1996T11349>. 

Compound 132 was formed from 0,0-diphenyldiamine with hexaethyltriamide of phosphorus acid (HEPA), as outlined in Scheme 9. This reaction was found to be nonselective and dependent on the reaction conditions employed. Heating the reaction mixture to 90-100 °C without solvent for an hour resulted in a mixture that upon sulfurization yielded compounds 132 and 133 <1997PS(123)89>. When the above reaction was carried out in xylene and heated to 120-130 °C, compound 134 was formed. Equilibrium was established between compound 134 and the dimer, compound 135, in a ratio of 3 2 (Equation 12). 

The reaction of the hexakis(cyclohexylamino)cyclotriphosphazene 136 with 3 equiv of antimony trichloride, in THF and in the presence of triethylamine, resulted in the formation of compound 137 (Equation 13). This compound was recrystallized from a mixture of THF and hexane and the crystal structure unambiguously assigned the structure <2005IC275>. The dimer, compound 138, was formed at room temperature from compound 139 and R3P (R = 7-Pr, Ph). Upon dissolution, compound 140 was formed <2002ZFA1903>. 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

Clark et al. [81] determined the time course of A-acetylation of primaquine by Streptomyces roseochromogenous and Streptomyces rimosus by quantitative high performance liquid chromatographic analyses of the culture broths. The A-5-bistri-fluoroacetyl derivative of primaquine was used as an internal standard in the analysis for the quantitation of primaquine A-acetate in microbial culture broths. S. roseochromogenous forms the highest level of primaquine A-acetate at 24—36 h after substrate addition, while S. rimosus is slower in its acetylation, peaking at 3 days after substrate addition. The formation of a novel dimeric compound from the reaction of primaquine with 8-(4-phthalimido-l-methylbutylamino)-6-methoxy quinoline is also reported. 

The conversion of functionalized arenes as represented by the general formula 97, into isothiazolium compounds (99) has been achieved by the sequence shown in Scheme 117.180 From a synthetic viewpoint, transformation of cyclopalladated products into thiocyanate derivatives is more efficiently achieved using monomeric dithiocarbamato complexes (98) rather than dimeric compounds. The generation of analogous dithiolylium perchlorates by a related procedure is described later (see Section IV,H). 

Diazaquinones are very sensitive to the nucleophilic addition of water thereby leading to the formation of dimeric compounds. Thus, pyrida-zinediones 68 provide 163, the corresponding maleic anhydride 164, and nitrogen (62JA966). Phthalazinedione 83a gave 165 likely in the same manner (Scheme 41). 

The electrochemical reduction of azulene with carbon, platinum, lead or zinc cathode does not give any product, whereas that with magnesium electrode yields a dimeric compound as the only reduction product, though the dimeric compound is easily transformed to the corresponding monomeric compound by a mild oxidation as shown in equation 2825. 

The existence of a germanium-carbon pjr-pjr double bond in the intermediate complex is likely. The intermediate was not isolated as such, but as its dimer. Compounds containing a carbon-germanium double bond were prepared by Satg6 and coworkers59, like the fluorenylidenedimethylgermanium, where stabilization arises from change transfer in the aromatic system. 

Metalation of Nitrones Metalation of cyclic aldonitrones in the absence of an external electrophile gives dimeric compounds, the nonmeta-lated aldonitrone group being the electrophile. At the same time, depending on... 

In contrast, there are two dimeric compounds to consider. One is the oxo,oxo derivative 6, the other a mixed oxo,thio 7 (3). The oxo groups in all of 5-7 occupy terminal positions, as usual, whereas the thio group in 7 is in abridging position. Each rhenium atom in 7 is therefore six-coordinate by virtue of a short rhenium-rhenium distance, 277.7 pm. Ignoring that bond, the local geometry about the one rhenium is a severely-distorted square pyramid, whereas the oxo-rhenium moiety has a geometry best described as a trigonal bipyramid. 

Extensive biotransformation studies have been conducted with the As-pidosperma alkaloid vindoline, but much less work has been done with monomeric Iboga and dimeric alkaloids from this plant. The long-standing interest in this group of compounds stems from the clinical importance of the dimeric alkaloids vincristine and vinblastine, both of which have been used for more than 2 decades in the treatment of cancer. Few mammalian metabolites of dimeric Catharanthus alkaloids have been characterized. Thus the potential role of alkaloid metabolism in mechanism of action or dose-limiting toxicities remains unknown. The fact that little information existed about the metabolic fate of representative Aspidosperma and Iboga alkaloids and Vinca dimers prompted detailed microbial, mammalian enzymatic, and chemical studies with such compounds as vindoline, cleavamine, catharanthine, and their derivatives. Patterns of metabolism observed with the monomeric alkaloids would be expected to occur with the dimeric compounds. 

Photolysis of pentobarbitone (pentobarbital, 285) was achieved on a solution buffered to pH 11 with a low-pressure mercury lamp over 10 h. At this pH the mono anion was the main species present. The products identified were the dealkylated ethyl barbitone (286), the amide (294) and both diastereoisomers of the ureide (295). On more prolonged irradiation, there also appeared ethylhydroxybarbitone (287) and an unidentified dimeric compound. When ethylbarbitone (286) was photolysed in the same way, it gave (287) and 2-ethyl-2-hydroxymalonic acid. Finally, pentobarbitone was irradiated in molar sodium hydroxide solution, where the dianion would be the main form present, to give (295) with a small amount of (294) [175]. 

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