Double-bond addition, promotion

Cyclization. Intramolecular addition of a guanidino group to a double bond is promoted by Pd(OAc)2 (10 mol%) and Cu(OAc)2 (2.1 equiv.). Bicyclic products containing a bridgehead nitrogen atom are usually obtained in good yields. ... 

Dehydrochlorination of 1,1,2-trichloroethane at 500°C in the presence of a copper catalyst gives a different product, ie, cis- and /n7 j -l,2-dichloroethylene. Addition of small amounts of a chlorinating agent, such as chlorine, promotes radical dehydrochlorination in the gas phase through a disproportionation mechanism that results in loss of hydrogen chloride and formation of a double bond. The dehydrochlorination of 1,2-dichloroethane in the presence of chlorine, as shown in equations 19 and 20, is a typical example. 

Addition to the 6,7-double bond is also observed with 4-chloro-A -3-ketones (20). Attack at the 1,2-double bond occurs as well to give mainly the la,2a 6, 7j -dimethylene steroids (21) in addition to some la,2a 6a,7a-dimethylene compounds (22). Reaction at the 6,7-double bond in the 4-chlorotrienone series may be promoted by the —I effect of the 4-chloro group resulting in an increased positive character at Methylena-... 

The addition, therefore, follows Markovnikov s rule. Primary alcohols give better results than secondary, and tertiary alcohols are very inactive. This is a convenient method for the preparation of tertiary ethers by the use of a suitable alkene such as Me2C=CH2. Alcohols add intramolecularly to alkenes to generate cyclic ethers, often bearing a hydroxyl unit as well. This addition can be promoted by a palladium catalyst, with migration of the double bond in the final product. Rhenium compounds also facilitate this cyclization reaction to form functionalized tetrahydrofurans. 

Ferrocen-l,l -diylbismetallacycles are conceptually attractive for the development of bimetal-catalyzed processes for one particular reason the distance between the reactive centers in a coordinated electrophile and a coordinated nucleophile is self-adjustable for specific tasks, because the activation energy for Cp ligand rotation is very low. In 2008, Peters and Jautze reported the application of the bis-palladacycle complex 56a to the enantioselective conjugate addition of a-cyanoacetates to enones (Fig. 31) [74—76] based on the idea that a soft bimetallic complex capable of simultaneously activating both Michael donor and acceptor would not only lead to superior catalytic activity, but also to an enhanced level of stereocontrol due to a highly organized transition state [77]. An a-cyanoacetate should be activated by enolization promoted by coordination of the nitrile moiety to one Pd(II)-center, while the enone should be activated as an electrophile by coordination of the olefinic double bond to the carbophilic Lewis acid [78],... 

It has also been known for many years that sulfonyl groups, like carbonyl groups, promote the addition of nucleophilic reagents to carbon- carbon double bonds . The meta-directing properties of the S02Me group in electrophilic aromatic substitution were discovered in the mid-1920s . ... 

The elimination is promoted by oxidation of the addition product to the selenoxide by f-butyl hydroperoxide. The regioselectivity in this reaction is such that the hydroxy group becomes bound at the more-substituted end of the carbon-carbon double bond. The regioselectivity of the addition step follows Markovnikov s rule with PhSe+ acting as the electrophile. The elimination step specifically proceeds away from the oxygen functionality. 

Light of the ultraviolet region promotes addition of water at the A9-10 double bond to form the lumi-compounds. Thus reactions are best carried out in the light of red or yellow photographic darkroom bulbs, and storage should be in opaque or amber bottles. 

Addition to Double Bonds and Elimination Reactions. Both Lewis and Br nsted acidity of mineral surfaces can promote addition and elimination reactions (37). Equation 14 shows an example for an addition/elimination equilibrium catalyzed by Br nsted acidity ... 

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. 

All these reactions are promoted by Pd(II) species, and can be stoichiometric (Eq. 10) or catalytic (Eqs. 11-13, in the presence of Cu(II) salts or other oxidizing agents). 3-Chloropropionyl chloride from ethylene is conceivably formed through PdCl2 addition to the double bond followed by CO insertion and reductive elimination (Scheme 2). 

The reaction sequence for a typical vinyl polymer has four steps. In the first step, a free radical must be produced from the initiator such as those shown in Figs. 2.18 and 2.19. These radical formation reactions are typically first order in rate and are promoted by the elevated temperature of the reaction. For some free radical initiators, light can also promote the reaction. Then a sequence of events in the reaction mixture occurs, including initiation of a chain, followed by propagation, and finally termination of the chain. Termination of the chain will be discussed later. The schematic steps to produce an addition polymer from bulk or solvent polymerization are detailed in Fig. 2.19. The radical produced from the initiator reacts with the monomer in Step 2 to produce a new free radical by opening the double bond of a... 

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