Double bond addition across

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

As shown in (5.84b), the characteristic feature of the Diels-Alder reaction is the addition of an ethylenic double bond (dienophile) across the 1,4-positions of a conjugated diene to give a cyclohexene ring product. The ethylenic bond is usually... 

Unlike the addition of halogens across double bonds, addition of acids results in formation of asymmetrical products. Specifically, a different group is added to each side of the double bond. Thus, if this reaction is applied to asymmetrical olefins such as propene, multiple products might be expected to form as illustrated in Scheme 7.8. In fact, while a mixture of products is formed, there is an overwhelming presence of the secondary substituted product compared to that with substitution at the primary position. This preference of reaction products resulting from addition of protic acids across double bonds is governed by Markovnikov s rule. 

In 1982, Casey and co-workers reported the first reactions that could be considered hydrocarbations because they involved the direct C-H bond addition across the C-C double bond of alkenes. They showed that the cationic bridging iron methylidyne complex undergoes this type of reaction with alkenes with anti-Markovnikov regioselectivity. No other hydrocarbation reactions had been reported until recently, when Kubiak and co-workers reported hydrocarbation reactions of a nickel carbene complex with alkenes. Thus, the dicationic aminocarbene complex 31 reacts with ethylene, resulting in a complete conversion to the ethylcarbene complex (Scheme 1). 

That looks simple and direct don t it If safrole was used as the alkene one would get safrole-azide as product. Just one teensy little reduction away from MDA. Strike also found some azide papers that, with a little work, will get safrole-azide in a totally different way. Strike came across a lot of work where groups were using dinucleophilic addition to get an azide and a halogen added across a double bond. The azide would always go to the beta secondary carbon and the halogen to the primary carbon (just what one would want if safrole was the substrate). 

Cyclodienes. These are polychlorinated cycHc hydrocarbons with endomethylene-bridged stmctures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocyclopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the ftve-membered ring forms the two isomers of chlordane [12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3t ,4,7,7t -hexahydro-4,7-methano-lJT-indene, QL-trans (mp 106.5°C) and pt-tis (32) (mp 104.5°C). The p-isomerhas signiftcantiy greater insecticidal activity. Technical chlordane is an amber Hquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 fig/L. It has rat LD qS of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

Isocyanates are Hquids or soHds which are highly reactive and undergo addition reactions across the C=N double bond of the NCO group. Reactions with alcohols, carboxyUc acids, and amines have been widely exploited ia developiag a variety of commercial products. Cycloaddition reactions involving both the C=N and the C=0 double bond of the NCO group have been extensively studied and used for product development (1 9). 

Gycloaddition Reactions. Isocyanates undergo cyclo additions across the carbon—nitrogen double bond with a variety of unsaturated substrates. Addition across the C=0 bond is less common. The propensity of isocyanates to undergo cycli2ation reactions has been widely explored for the synthesis of heterocycHc systems. Substrates with C=0, C=N, C=S, and C=C bonds have been found to yield either 2 + 2, 2 + 2 + 2, or 2 + 4 cycloadducts or a variety of secondary reaction products (2). 

There are a few economical routes that can be employed for production of the largest-volume phosphines as specialty chemicals. The preparation of alkyl phosphines, where R > C2H, employs the addition of lower phosphines across an olefinic double bond. The reaction may be either acid-, base-, or radical-catalyzed. The acid-catalyzed addition probably proceeds through the generation of a carbonium ion intermediate which is attacked by the unshared... 

The fatty acids obtained from the process can be used directly or further manipulated for improved or modified performance and stabiUty. Hardening is an operation in which some fraction of the unsaturated bonds present in the fatty acids are eliminated through hydrogenation or the addition of H2 across a carbon—carbon double bond. This process was initially intended to improve the odor and color stabiUty of fatty acids through elimination of the polyunsaturated species. However, with the growth in the use of specialty fatty acids, hydrogenation is a commercially important process to modify the physical properties of the fatty acids. 

The symmetrical diesters are produced by esterification of maleic anhydride, followed by addition of sodium bisulfite across the double bond (see... 

Polyurethane Formation. The key to the manufacture of polyurethanes is the unique reactivity of the heterocumulene groups in diisocyanates toward nucleophilic additions. The polarization of the isocyanate group enhances the addition across the carbon—nitrogen double bond, which allows rapid formation of addition polymers from diisocyanates and macroglycols. 

Hydrolysis of vinyl acetate is catalyzed by acidic and basic catalysts to form acetic acid and vinyl alcohol which rapidly tautomerizes to acetaldehyde. This rate of hydrolysis of vinyl acetate is 1000 times that of its saturated analogue, ethyl acetate, ia alkaline media (15). The rate of hydrolysis is minimal at pH 4.44 (16). Other chemical reactions which vinyl acetate may undergo are addition across the double bond, transesterification to other vinyl esters, and oxidation (15—21). 

Initiation is an electrophilic addition of a cation across the double bond, but because of the poor nucleophilicity of the initiator s counterion. 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

Hydrogen cyanide adds to an olefinic double bond most readily when an adjacent activating group is present in the molecule, eg, carbonyl or cyano groups. In these cases, a Michael addition proceeds readily under basic catalysis, as with acrylonitrile (qv) to yield succinonitnle [110-61-2], C4H4N2, iu high yield (13). Formation of acrylonitrile by addition across the acetylenic bond can be accompHshed under catalytic conditions (see Acetylene-DERIVED chemicals). 

Additional nitrogen atoms facilitate such reactions, particularly if they are a or y to the alkyl group, and, if a, act across a formal double bond. Thus, the 5-methyl group in 3,5-dimethyl-l,2,4-oxadiazole is much more reactive than the 3-methyl group in this compound or the methyl groups in 2,5-dimethyl-l,3,4-oxadiazole (76AHC(20)65). 

In 2,1-benzisoxazoles, halogenation with CI2 or Br2 leads to substitution in the 5-position, although the reaction appears to behave as a simple addition across a double bond. A... 

Acid treatment or thermolysis of aziridinyl phenyl ketone oxime generated a 2-isoxazoline (74JAP(K)74i 17462), while treatment of a diphenylcyclopropene (486) with NOCl generated a 2-isoxazoline in contrast to dialkylcyclopropene (487) which produced addition across the double bond (Scheme 126) (73MI41605). 

An alternative route to cross-linking is to start with a linear polymer and then cross-link the molecules by tying the molecule through some reactive group. For example, it is possible to cross-link unsaturated polyesters by an addition polymerisation across the double bond as shown schematically in Figure 2.12. 

Since cross-linking occurs via an addition mechanism across the double bonds in the polyesters and the reactive diluent there are no volatiles given off during cure (c.f. phenolic and amino-resins) and it is thus possible to cure without pressure (see Figure 25.1). Since room temperature cures are also possible the resins are most useful in the manufacture of large structures such as boats and car bodies. 

Reactions of the halogen iluorides with other unsaturated functional groups are generally reported only with highly fluorinated substrates Hexafluorobenzene and denvatives [118] and octaflvoronaphthalene [119] react with mixtures of bromine and bromine trifluoride by 1,4 addition of fluorine followed by addition of bromine fluoride across a reniatning double bond (equation 22)... 

Hydroxylation, the addition of two hydroxyl groups across a double bond, converts fluonnated alkenes to different products depending on the presence or absence of a fluorine atom at the hydroxylated carbon... 

Acid-Catalyzed Additions across Double Bonds... 

Stannanes also add across double bonds offiuonnated olefins in a free radical reaction Trimethylstannane undergoes stereospecific addition to hexafluorocyclo-butene to afford trans 1,2,3,3,4,4 hexafluoro 1 (trimethylstannyl)cyclobutane [5] (equation 1)... 

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