Dimerization derivatives

The N-silylated enol acetate 1523 is cyclized by TMSOTf 20 in CHCI3, in 95% yield, giving the oxazole 1524 [57]. The dimeric derivative 1525 affords the 2,2 -bis-oxazole 1526 in 46% yield [57]. 2-Benzoylamino-3-chloropyridine 1527 is cyclized by polyphosphoric acid trimethylsilyl ester (PPSE) 195 on heating for 15 h in boiling 1,2-dichlorobenzene to give 40-60% 2-phenyloxazolo[5,4-f)]pyridine 1528 [58] (Scheme 9.34). 

Roher AE, Chaney MO, Kuo YM, Webster SD, Stine WB, Haverkamp LJ, Woods AS, Cotter RJ, Tuohy JM, Krafft GA, Bonnell BS, Emmerling MR. Morphology and toxicity of Abeta-(l-42) dimer derived from neuritic and vascular amyloid deposits of Alzheimer s disease. J Biol Chem 1996 ... 

In the past decade, Ishikawa et al. have investigated the photochemistry of aryldisilanes.66 73 76 84 Lately, dimers derived from these unusual silenes have been observed from the first time.78 Thus, photolysis of 1,4-bis(penta-methyldisilyl)benzene 76 in hexane presumably gave rise to the silene 77 but, on workup employing crystallization, two head-to-head stereoiso-meric dimers 78 and 79 were obtained in about 45% yield in a 1 1 ratio. These were said to be formed from the silenecyclohexadienes 77 by the two alternative pathways shown in Scheme 12. Related dimers were also... 

Prior to 1958 only nitrile-adducts were reported to result from the reaction of nitriles with trihaloboranes (c.f. 36)). The first reported example of the 1,2-addition of boron-halogen bonds to a C=N group involves the reaction of tri-fluoroacetonitrile with trichloroborane or tribromoborane 4) and leads to dimeric derivatives. A 1 1 ratio of the cis-trans isomers is obtained as indicated on the basis of 19F n.m.r. studies. 

We later determined that with lower catalyst loadings (15 mol% 2), reaction efficiency suffers (<50% conversion). When Ru complex lb was used (20 mol%, benzene, 80°C), 5-10% dimer derived from reaction of the terminal olefins was formed as the only product. Continued investigation of the catalytic macrocycli-zation indicated that, with freshly prepared and recrystallized Mo catalyst, the metathesis process occurs smoothly at 22 °C to afford 2 in 90% isolated yield after only 4 h. With 40 mol% 2, the yield improved to 97%, and less than 20 mol% catalyst gave notably lower conversions and yields. 

Molecular scaffoldings with tetraethynylethenes (TEEs, 3,4-diethynylhex-3-ene-l,5-diynes) and trans-1,2-diethynylethenes [DEEs, (E)-hex-3-en-l,5-diynes] are at a particularly advanced stage.114,37 38 441 A collection of dose to one hundred partially protected and functionalized derivatives have been prepared in the meantime, providing starting materials for the perethynylated dehydroannulenes and expanded radialenes shown in Figure 6.136 441 TEEs and DEEs, as well as dimeric derivatives substituted at the terminal alkynes with donor (D, p-(dimethyl-... 

Delmas P, Abogadie FC, Milligan G, Buckley NJ, Brown DA (1999) Py dimers derived from Go and Gj proteins contribute different components of adrenergic inhibiton of Ca channels in rat sympathetic neurons. J Physiol 518 23-36 Diverse-Pierluissi M, Inglese J, Stoffel RH, Lefkowitz RJ, Dunlap K (1996) G protein-coupled receptor kinase mediates desensitization of norepinephrine-induced Ca channel inhibition. Neuron 16 579-585 Docherty JR (1998) Subtypes of fimctional ap and a2-adrenoceptors. Eur J Pharmacol 361 1-15... 

Osmium tetroxide hydroxylations can be highly enantioselective in the presence of chiral ligands. The most highly developed ligands are derived from the cinchona alkaloids dihydroquinine and dihydroquinidine.40 The most effective ligands are dimeric derivatives... 

The highly substituted derivative 186, in the form of the potassium salt, has been recommended for use in detonators in place of the more dangerous mercury fulminate. l,2,3-Benzotriazine-4-thione (39, R — H) has been used in photographic transfer emulsions as an inhibitor and toning agent, and heavy metal salts of the oxygen analog 10, R = H are employed as photodevelopable emulsions. The latter compound is also claimed to be useful as a stabilizer in olefin polymers and as an antioxidant in certain other polymers. Dimeric derivatives of 10 have... 

The synthesis of lanthionines via dehydroalanines has been carried out using an (9,5-di-benzoylated Z-L-Cys-L-Ser-OMe. 31 Using (3-elimination under basic conditions in sodium methoxide and subsequent intramolecular Michael addition, the corresponding L-lanthio-nine derivative was formed. However, as a final step the cyclolanthionyl dipeptide would have to be cleaved at the amide bond to obtain lanthionine. The same authors reported the use of the O-tosylated serine dipeptide which was subjected to (3-elimination, forming the desired dehydroalanine derivative. However, this synthesis also yielded cyclic L-lanthionine dimers as a result of an intermolecular Michael addition. The amounts of cyclolanthionine and lanthionine dimer derivatives depended on the initial concentration of the dipeptides. In addition, the directed synthesis of cyclic lanthionine dimers, which were produced from N-benzyloxycarbonyl-W-trityllanthionine monomethyl ester, has been reported. 32 ... 

The second electronic transfer to the oxygen produces the diradical (C) which evolves into monomer formation. The latter possibility (IV) is a homolytlc cleavage giving another anion radical. If the process follows scheme III or IV, we must obtain monomer formation after the oxidation reaction in all cases. We have carried out the oxidation of carbanionic dimers derived from isoprene, crmethylstyrene, styrene, 1,1-diphenylethylene. 

An interesting dimer derived from tetrakis(trifluoromethyl)cyclobutadiene 40 is obtained by photolysis of an ozonide precursor. The diene is stable at — 196°C but forms dimer 41 upon... 

Chapman and Breslow synthesized zinc(II) complexes of monomer and dimers derived from 1,4,7-triazacyclododecane with phenyl 48 and 4,4 -biphenyl linkers 49 (55). They were examined as catalysts for the hydrolysis of 4-nitrophenyl phosphate (NP2 ) and bis(4-nitrophenyl) phosphate (BNP ) in 20% (v/v) DMSO at 55°C. On the basis of the comparison of the pseudo-first-order rate constants, the dinuclear zinc(II) complexes 48 with 1,3-phenyl and 1,4-phenyl linkers are ca. 5 times more efficient than monomer or 49 in the hydrolysis of NP2, leading to the conclusion that the two zinc(II) ions are simultaneously involved in the hydrolysis, as in the enzyme alkaline phosphatase. For the hydrolysis of BNP, a longer dimer 49 is ca. six times more effective than 1,3-phenyl-linked dimer 48 and monomers. 

C) [79AG(E)1], and 3-fluoropyridine affords 3,3 -difluoro-4,4 -bipyridine (25%) and other dimeric derivatives (KNH2/liq. NH3) (64TL3207). 

Nitro-compounds fRNOj) are isomeric with nitrites, but their electronic structure, excited states and photochemistry are very different. There is no very low-lying (n.jt ) state, and nitroalkanes show n — 3i absorption with a maximum around 275 nm ( —201 mol - cm In cyclohexane solution, nitromethane (CH1NOi) is photoreduced to nitrosomethane(CH,NO, but nitroethane under the same conditions gives rise to a nitroso-dimer derived from the solvent CS.47). The latter process is probably initiated by cleavage of the carbon-nitrogen bond in the nitroalkane. In basic solution (when the nitroalkane is converted to a nitronate anion) irradiation can lead to efficient formation of a hydroxamic acid (S.48), and this reaction most likely proceeds through formation of an intermediate three-mem bered cyclic species. 

A revitalization of interest in the copolymerization of epoxides and C02 can be traced to studies involving discrete zinc complexes. Several well-defined zinc monomeric and dimeric derivatives have been shown to be effective catalysts for the coupling of CHO and C02 to afford copolymers with high degrees of C02 incorporation. These include reports of sterically encumbering Ms-phenoxide derivatives of zinc [24], a highly fluorinated zinc carboxylate [25], and zinc [3-diiminate complexes [26] (see Figure 8.2). 

Quinazolines are of great interest in the pharmaceutical industry as protein tyrosine kinase inhibitors. Dener et al 8 described a synthesis starting from 2-methoxybenzaldehyde, Wang, or Rink resins. With the aldehyde resin reductive aminations were undertaken to yield polymer-bound secondary amines (Fig. 7). The latter were subjected to 2,4-dichloro-6,7-dimethoxyquinazoline to give the 4-amino-substituted derivatives. These were then allowed to react with primary or secondary amines at 135-140° in the presence of DBU in DMA. As a result of a detailed scope and limitation study, Dener et al,28 note that some bifunctional amines, such as piperazine, give to some extent dimeric derivatives. 

The molecular geometries of nitrogen squaric acid and its dimeric derivatives have been optimized at RHF/6-311+G and RB3LYP/6-311+G levels of theory.3 The... 

A-OC3H6COOH 3-Carboxy propyl DBP TBP Dimer Derivatives Traces Total 88,000 ppm or 8.8%... 

The Wurtz Coupling is one of the oldest organic reactions, and produces the simple dimer derived from two equivalents of alkyl halide. The intramolecular version of the reaction has also found application in the preparation of strained ring compounds ... 

Delmas P, Abogadie FC, Milligan G et al (1999) betagamma dimers derived from Go and Gi proteins contribute different components of adrenergic inhibition of Ca2+ channels in rat sympathetic neurones. J Physiol 518 23-36... 

Syntheses and X-ray structures have been reported for (53) [94T11205] and (54) [95MI645], The preparation and non-linear optical properties of 2-imino-l,3-dithioles (55) have been described [95MI35] and the dimeric derivatives (R3 = p-phenylene) have also been reported [94BSF774]. The product (56), obtained from reaction of 4-methyl-5-phenyl-l,2-dithiol-3-thione with DMAD, undergoes cycloaddition with a further molecule of DMAD to afford the spiro compound (57) whose structure is confirmed by X-ray methods [94KGS908]. 

Fig. 21 DFT-computed structures of the two products of association of further diisopropy-lzinc with the homoehiral square dimers derived from 2-methylpyrimidinal.

The introduction of mercury(n) into an interchain disulphide bond in a Bence-Jones dimer derived from immunoglobin has been reported.258 An electron density map of the 2-protein using the mercury(n) derivative has been obtained.259 It is possible that this may show where the antigen activity of immunoglobin resides. 

U.S. Patent 4,252,887 (February 24, 1981) Dimers derived from unsymmetrical... 

Rewcastle and co-workers have also reported a concise synthesis of an indole-fused analogue 320, together with some of the dimeric derivative 321 [01T7185], while Rees et al. have described a novel oxime 322 to pentathiepine 324 cascade reaction induced by S2CI2 the 1,2,3-dithiazole 323 is also formed [01CC403],... 

Recently, White (32) observed that under certain conditions ( —15°C., large excess of amine base) oxidation of the dimer derived from 2,6-xylenol with a limited amount of preoxidized copper complex yielded the tetramer as the major product, with small amounts of hexamer and only traces of monomer and trimer. The two rings are indistinguishable in this case, but there is little doubt, in view of the results of Mijs, that... 

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