Reactions of the Double Bond

The double bond of N-acylenamino acids and their esters represents the locus minoris resistentiae . As a result of conjugation with the carboxyl group, the double bond is a good acceptor for nucleophilic addends under basic catalysis. The acylamino group makes electrophilic additions possible. It is thus possible to obtain a- or P-mercapto a-amino acid derivatives by selecting the appropriate reaction conditions for the addition of mercaptans. 

Besides polar additions, radical additions such as the photochemical (287) or peroxide-catalysed (121, 122) mercaptan addition have been investigated. Catalytic hydrogenation has been the object of particularly thorough study. In cases where optical induction is possible, addition reactions afford a means of synthesizing optically active amino acids. 

N-Acyl-dehydro-amino-butyric acid derivatives 

The addition of CH-acidic compounds, hydrogen cyanide and amines to acylaminoacrylic acid compounds has occasionally been employed for the synthesis of more complex amino acids. 

Reduction with sodium borohydride and tritiated sodium boro-hydride (28, 61,144,164, 434) has been used in the structural elucidation of natural products with dehydroamino acid units, as has the addition of mercaptans or nitromethane. Addition of S-nucleophiles is the method of choice for the preparation of sulfur-containing amino acids such as cysteine, penicillamine, lanthionine and cystathionine. Such additions have also been often carried out in biomimetic experiments in the study of penicillin biosynthesis (see Table 3). 

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The presence of the unsaturated substituent along this polyester backbone gives this polymer crosslinking possibilities through a secondary reaction of the double bond. These polymers are used in paints, varnishes, and lacquers, where the ultimate cross-linked product results from the oxidation of the double bond as the coating cures. A cross-linked polyester could also result from reaction (5.J) without the unsaturated carboxylic acid, but the latter would produce a gel in which the entire reaction mass solidified and is not as well suited to coatings applications as the polymer that crosslinks upon drying. ... 

Reactions of the double bonds include isomerization and conjugation, cyclization, various addition reactions including hydrogenation, pyrolytic and... 

There are over 400 different commercial alkyd resin formulations based on phthalic anhydride used in the coatings business. Alkyd resins for paints are made by reacting phthalic anhydride with a poly-alcohol (usually from naturally occurring sources rather than synthetic) that contains unreacted double bonds. The paint dries by the resin crosslinking through reaction of the double bonds under the influence of oxygen in the air. 

Different results were obtained using allylic alcohols as terminating agents. In spite of the expected reactivity of the alcoholic function as hydrogen donor only products deriving from the reaction of the double bond were obtained (23) according to the general pattern previously described for Heck-type reactions with allylic alcohols (24). 

Selenium dioxide is also an oxygen donor to alkenes. In this case, however, the initial reaction of the double bond is with the selenium center followed by two pericyclic steps. After hydrolysis of the organo-selenium intermediate, the result is a hydroxylation at the allylic carbon position65. Thus, limonene (2) yields racemic p-mentha-l,8(9)-dien-4-ol66. The high toxicity of selenium intermediates and prevalence of many rearrangements has limited the widespread use of the reagent in synthesis. 

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

The double bonds in 2,3-dihydro-l,4-dioxin, 2,3-dihydro-l,4-oxathiin and 2,3-dihydro-1,4-dithiin undergo standard electrophilic addition reactions. Under acid catalysis, methanol adds to 2,3-dihydro-l,4-oxathiin to give 2-methoxy-1,4-oxathiane (66HC(21-2)842). Various examples are available of reactions of the double bonds with carbenoids to give bicyclo[4.1.0]diheteroheptanes (77LA910,78ZC15), and with alkenes in [2 + 2] cycloadditions (78CB3624). 

Cis- and fraws-cyclooctene, 100 and 102 respectively, and their derivatives 103-107, all undergo ROMP295 also 10862,362,109 and 11062, 111-113362, 114363,115364,116365, 118362, 119 and 120366,367. Only 101295 and 117362 fail to polymerize, perhaps due to unfavourable choice of catalyst and conditions. The trans monomer 102 gives a 43% cis polymer very rapidly in the presence of MoCl2(PPh3)2(NO)2/EtAlCl2368 and is polymerizable by 18110. With a catalyst of type 10 secondary metathesis reactions of the double bonds in the polymer of 100 cause the cis content to fall from 75% to 25% as the reaction proceeds271. 

Figure 13 shows the reaction of the double bond with Mercury (II) acetate (50). In a fast reaction the double bonds at the surface react. Subsequently controlled by a slow diffusion process, the double bonds in the interior of the particle react. The specific surface of these systems is 200 to 300 m2/g. As enzyme carriers they should be well-suited, as support for polymeric reagents more knowledge about the possibility of localizing the reaction at the surface is needed. 

All alkenes have a common feature a carbon-carbon double bond. The reactions of alkenes arise from the reactivity of the carbon-carbon double bond. Once again, the concept of the functional group helps to organize and simplify the study of chemical reactions. By studying the characteristic reactions of the double bond, we can predict the reactions of alkenes we have never seen before. 

RCM and RORCM reactions in the presence of Grubbs catalysts 151 <1996JA100> and 152 <19990L953> have also been employed for catenane synthesis under reversible thermodynamic conditions. The isomeric ( /Z)-mixture of [2]catenanes 179 was obtained <1998NJC1019> by RCM of an appropriate diimide bearing ethenyl-terminated alkyl chain in the presence of crown ether 170 and catalyst 151. Similarly, initial pseudorotaxane formation followed by metathesis reaction of the double bonds present on the secondary alkylammonium ion axle has afforded [3]catenane 180 as well as [2]catenane 181 <2003TL5773>. 

The oxidation of thioethers on TS-1, Ti-P and Ti,Al-P produced corresponding sulfoxides and, more slowly, sulfones by consecutive oxidation [144—149]. AUyl methyl thioether was oxidized selechvely on sulfur, with no reaction of the double bond [148]. The kinetic law was obtained for the oxidation of dibutylsulfoxide on Ti,Al-P [147]. 

The oil is fairly pure as extracted, has a light color, and because the double bonds are well separated, it is resistant to oxidation. The oil can be chemically modified by reaction of the double bonds (hydrogenation, stereomutation, epoxidation, sulfo-chlorination) (197). 

The alkyl groups attached to the doubly-bonded carbons modify the reactions of the double bond the double bond modifies the reactions of the alkyl groups. 

Allylic and propargylic 3-keto sulfoxides could be reduced as well as saturated compounds. Optically active allylic 3-hydroxy sulfoxides present some specific interest because of the possible hydroxylation of the double bond leading to vicinal triols. The osmium tetroxide catalyzed hydroxylation reaction of the double bond in the presence of trimethylamine N-oxide is highly stereoselective the (/ ,/ )-3-hydroxy sulfoxide gave only one diastereoisomeric triol as a result of a cis hydroxylation of the double bond and a symbiotic effect of the two chiral centers in the asymmetric induction (the (S,/ )-isomer gave a lower de). 

Although some authors 1 prefer to discuss the various reactions of carbon-carbon double bonds in terms of 7r-clect rons, it may be simpler for the present discussion to consider reactions of the double bond as proceeding through intermediates such as B or C. 

Next, the reaction of the double bond of benzvalene will be discussed. Benzvalene itself may be reduced with diimine whereby the bicyclobutane part remains unaffected (79) 73). 

The reaction of the double bond to form crosslinked networks and the chemorheology of these systems are considered later. Different acid and diol starting materials result in polyester resins with superior properties. For example, the use of iso-phthalic acid instead of phthalic anhydride (that produces ortAo-phthalate units) results in improved water resistance of the resins, but at increased cost. 

The maleimide group in BMI can undergo a wide range of possible reactions, either in the neat resin or copolymerized, with other monomers. The predominant reaction is the free radical chain reaction of the double bond ([20, 21] and references therein), which, due to the difunctionality of BMI monomers, results in a crosslinked three-dimensional network. Maleimides have been shown to undergo copolymerization with a number of monomers including methyl methacrylate [22, 23], styrene [22-24], acrylonitrile [22] and... 

Some chemists would argue that the reactions of the double bonds are stereospecific, but the reaction of the triple bond is not. Their argument is that, for a reaction to be stereospecfic, a specfic diastereomer of starting material must lead to a specfic diastereomer of product and this implies that there is an alternative diastereomer of starting material which would give the alternative diastereomer of product. BUT, since the actylene has no diastereomer, this cannot be stereospecific. 

Structural features of olefins with distorted double bonds have been discussed within the deformation space defined by the eight bond angle deformations. The out-of-plane bond angle distortions are of particular interest because they are involved in addition reactions of the double bond. The symmetrical Blg-type deformation is related to concerted anti-additions, whereas the J3lu-type distortion (cf. Table 1) is appropriate for concerted syn-addition and those reactions that involve three-center intermediates and the formation of transition metal complexes. Twist or torsion is due to the Alu-type oop distortion and may be related to addition reactions, which in principle would lead—in the extreme case of a 90° twist angle—to an eclipsed rather than a staggered arrangement. 

Various examples are available of reactions of the double bond with alkenes in [2-1-2] cycloadditions. Thus, photochemical cycloaddition of 2,3-dihydro-1,4-dioxin to 3-methylcyclohex-2-en-... 

Reactions of alkenes involve the carbon-carbon double bond. The key reaction of the double bond is the addition reaction. This involves the addition of two atoms or groups of atoms to a double bond. The major alkene addition reactions include addition of hydrogen (Hj), halogens (Clj or Brj), water (HOH), or hydrogen halides (HBr or HCl). A generalized addition reaction is ... 

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