Bond substituted

Next an alkyl halide (the alkylating agent) is added to the solution of sodium acetylide Acetylide ion acts as a nucleophile displacing halide from carbon and forming a new carbon-carbon bond Substitution occurs by an 8 2 mechanism... 

X-ray diffraction analysis of crystalline poly(schiff base)s and their low molecular models shows that the formation of molecular complexes is accompanied by an increase in interplanar distances and, in a number of cases, by complete amor-phization. Molecular complexes of poly(schiff base)s with Br2 decompose with time, because of the bromination of the donor components, forming C—Br bonds. Substitution of hydrogen by bromine in phenyl groups occurs only in cases in which these groups are not included into the main polymeric chain. 

The addition of an ion to butadiene is clearly an exothermic process in the gas phase due to the formation of aa-bond substituting a rc-bond. The agreement of the reaction enthalpies of the reactions (11) and (12) with equal R (except R = H) is surprising (Table 11). 

Slee and LeGoff performed further investigations on the reaction of dimethyl acetylenedicarboxylate 4-20 with an excess of furan 4-21, as first described by Diels and Alder (Scheme 4.5) [la]. At 100 °C, 4-24 and 4-25 were not produced (as proposed), but rather 4-22 and 4-23, since at elevated temperature an equilibrium takes place and the primarily formed 4-24 and 4-25 isomerize to give a 6 1-mixture of the exo-endo and the exo-exo products 4-22 and 4-23, respectively. However, at lower temperature, in the primarily formed [4+2] cycloadduct the double bond substituted with the two carbomethoxy group acts as the dienophile to give the two products 4-24 and 4-25 in a 3 1 ratio with 96% yield within five weeks, as has been shown by Diels and Olsen [la,lc]. For a differentiation of these two types of adducts, Paquette and coworkers [7] used a domino and pincer product . The Cram group [8] described one of the first examples of a reaction of a tethered bisfuran 4-26 with dimethyl acetylenedicarboxylate 4-20a to give 4-27. 

DOUBLE INSERTION IN REACTIONS OF GLYCINE DERIVATIVES REARRANGEMENT OF SYMMETRICAL ANHYDRIDES TO PEPTIDE-BOND-SUBSTITUTED DIPEPTIDES... 

Further studies demonstrated the influence of the double-bond substitution on both the reactivity and the stereoselectivity of the reaction [78-81]. Tamaru and co-workers reported then that using the same PdCl2/CuCl2/MeOH system on butenol derivatives, with the double bond in either the terminal or an internal position, furnished selectively y-butyrol-actones. This dicarbonylation process most probably includes (i) a lactoniza-tion step and (ii) a methoxycarbonylation step, as displayed in Scheme 11 in which we clarify some intermediate steps on a representative example [82, 83]. The use of propylene oxide as an additive promotes this Pd-catalyzed dicarbonylation by playing the role of an HC1 quencher to maintain neutral conditions. 

Rhenium(0) compounds are rare and frequently lie in the realm of the organometallic chemistry. A simple example is decacarbonyldirhenium(0) in which two staggered, square-pyramidal Re(CO)5 fragments are held together by a single rhenium-rhenium bond. Substitution of carbonyl ligands is possible by tertiary phosphines and arsines, silanes and isocyanides, and binuclear Re-Re, Mn-Re, and Co-Re complexes have been studied. " Successive replacement of CO ligands can readily be observed by vibrational spectroscopy. This has been demonstrated... 

Chlorination of natural rubber (NR) is carried out with chlorine in carbon tetrachloride solution at 60-90°C to yield a chlorinated rubber containing about 65% chlorine, which corresponds to 3.5 chlorine atoms per repeat unit. The process is complex and includes chlorine addition to the double bond, substitution at allylic positions, and cyclization. Chlorinated rubber has high moisture resistance and is resistant to most aqueous reagents (including mineral acids and bases). It is used in chemical- and corrosion-resistant paints, printing inks, and textile coatings. Bromination of butyl rubber is also practiced [Parent et al., 2002]. 

Xmax is shifted to 410 nm in 44 (c and g annelation) it is shifted to 422 nm. The explanation of this effect is quite straight forward. Benzo-annelation across a double bond substitutes a bond with half double bond character for a double bond. In terms of the exciton model this decreases both the length of the interacting system and the strength of the interaction. 

FLUOROOLEFIN DIPEPTIDE ISOSTERES 2.1. Alkenes as amide bond substitutes... 

S)-[ F]fluoroethylcarazolol 8, 111 subtypes of, 100 Adriamycine (doxorubicine), 589 Agrochemical agents, 215 AIF. See Aluminium monofluoride Aliphatic nucleophilic substitution, 28 Alkenes, as amide bond substitutes, 702-703 Alkenes fluorination, 18 Allyl hydrazines as SSAO inhibitors, 674 Aluminium monofluoride, 534 Alumino-fluoride complexes, 364 Alzheimer s disease (AD)... 

Uncatalyzed addition reactions of Grignard reagents with nonconjugated alkenes and aUcynes are of limited use in synthesis. However, carbon-carbon double bonds substituted by a leaving group, such as an acetate, are susceptible to be displaced by organomagnesium compounds presumably by an addition-elimination pathway. A few examples have been reported (equation 64). 

H-Aziridines. In the presence of BF3 etherate, this reagent adds to double bonds substituted with three cyano or carboalkoxy groups to give an adduct that is converted into a I //-aziridine by treatment with triethylamine. 

The Dewar thiophene (2), possessing a strained double bond substituted with highly electronegative groups, undergoes cycloaddition with dienes (77JCS(P1)2355) and azides... 

Potassium hydroxide, 258 Trimethylsilyl chlorochromate, 327 of carbon-carbon double bonds substituted by heteroatoms m-Chloroperbenzoic acid, 76 of oximes to carbonyl compounds Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Trimethylsilyl chlorochromate, 327 of protected alcohols Chlorodimethylthexylsilane, 74 Formic acid, 137 p-Methoxyphenol, 181 of thioacetals and -ketals Methoxy(phenylthio)trimethyl-silylmethane, 182... 

The first and, possibly, the most intuitively satisfying among these concerns the nature of the lone pair and the fact that its participation into the w system bears unmistakable dependence on its mobility as controlled by the effective electronegativity of its heteroatomic host, the unit s suitability as a double-bond substitute decreasing in the order N > NH NAlkyl > S > NAcyl > O. It is further noted that this heteroatom-electronegativity effect is most spectacularly manifested in the unrestricted members of the (4n + 2 n series such as the nine-, thirteen-, and seventeen-membered rings where a change between the... 

Olefinic double bonds substituted with one or more electron-withdrawing groups show significant dipolarophilic activity in cycloaddition reactions with organic azides,43,276-278 similar to the electron-rich double bonds of enamines and enol ethers the reactivity is less pronounced in azide additions compared to that observed in diazomethane reactions.7 The first triazolines reported resulted by the action of aryl azides on benzoquinones.1,279-281 As a rule, stereospecific cis additions occur,32 which are usually unidirectional except in the case of methacrylic derivatives67 and certain alkenes bearing... 

Position of Double Bond Substitution at C-5 5 -Uradl Derivative... 

Photoisomerization of E-C=C double bonds substituted with heteroaromatic groups that allow intramolecular hydrogen bonding were found to afford one-way E - Z... 

Dearden, Rahman 1988 Hydrogen bonding Substituted anilines... 

Scheme 3. C-H bond substitutions of saturated hydrocarbons with photoexcited TCB.

Cleavage of vie-diols. C—C bonds substituted by hydroxy groups are cleaved by this system to ketones and carboxylic acids in high yield. Di-lerl-diols are cleaved... 

When the [2+2+2] cycloaddition of 1,6-diynes occurred in the presence of C=C bonds or C=N bonds, substituted benzenes or pyridines were obtained in good yields [95-98]. For example, anthraquinones were produced by reaction of l,2-bis(propiolyl)benzenes with a variety of monoalkynes [95] (Eq. 74). 

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