Substituent effect substituted olefin

Jones and Vogel investigated the snbstitnent effect of a 5,6-bis(methoxycarbonyl) group in bicyclo[2.2.2]octene (48i) [117]. The substituent effect of a single 5-exo substituent on the facial selectivities of bicyclo[2.2.2]octenes 48b-48h was also characterized by our group [118]. Epoxidation and dihydroxylation of the olefin moiety of 5-exo-substituted... 

Nishiyama et al. introduced a new catalyst, the chiral tr<2 i -RuCl2(Pybox-i-Pr)(ethylene) complex (91), which showed for the first time both enantio- and diastereoselectivity (trans-selectivity) at excellent levels in the reactions of terminal olefins (Scheme 66).251-253 With 4-substituted Ru(Pybox-i-Pr) complexes (92), they studied the substituent effect on enantioselectivity... 

Cycloaddition of a nitrile oxide to a substituted olefin can lead to two regio-isomers, the 4- and/or 5-substituted 2-isoxazoline. Reactions of monosubstituted alkenes give the 5-substituted isomers 18 with almost complete regioselectivity (10,15,30,109). This result is also supported by ab initio and FMO calculations (114,119). Change of substituents in the dipole has little effect on the regioselectivity of such reactions when monosubstituted alkenes are used (Table 6.4). 

The mechanism involves nucleophilic addition to a Z-substituted olefin followed by an intramolecular bimolecular nucleophilic substitution. Several side reactions also occur. Discuss the chemistry involved in this reaction, pointing out substituent effects at each stage. 

This obstacle can be overcome by moving electron withdrawing substituents away from the double bond and increasing the reactivity of double bond by positioning it in a strained ring. This is achieved using bicyclic monomers. The monomers are readily obtained from the Diels-Alder reactions of substituted olefins with cyclopentadiene. This route is effective also for fluorinated monomers. These types of monomers undergo a ROMP with a variety of one component and two-component initiator systems. 

Previous work has shown that the electronic characteristics of the benzene substituent in triarylphosphine chlororhodium complexes have a marked influence on the rate of olefin hydrogenation catalyzed by these compounds. Thus, in the hydrogenation of cyclohexene using L3RhCl the rate decreased as L = tri-p-methoxyphenylphosphine > triphenylphosphine > tri-p-fluorophenylphosphine (14). In the hydrogenation of 1-hexene with catalysts prepared by treating dicyclooctene rhodium chloride with 2.2-2.5 equivalents of substituted triarylphosphines, the substituent effect on the rate was p-methoxy > p-methyl >> p-chloro (15). No mention could be found of any product stereochemistry studies using this type of catalyst. 

The effect of monofluorination on alkene or aromatic reactivity toward electrophiles is more difficult to predict Although a-fluonne stabilizes a carbocation relative to hydrogen, its opposing inductive effect makes olefins and aromatics more electron deficient. Fluorine therefore is activating only for electrophilic reactions with very late transition states where its resonance stabilization is maximized The faster rate of addition of trifluoroacetic acid and sulfuric acid to 2-fluoropropene vs propene is an example [775,116], but cases of such enhanced fluoroalkene reactivity in solution are quite rare [127] By contrast, there are many examples where the ortho-para-dueeting fluorine substituent is also activating in electrophilic aromatic substitutions [128]... 

If steric hindrance is important we should see evidence for this in the effect substitutents in the olefin have on the orientation ratio (see Table 14). The first feature to notice about Table 14 is that the methyl and trifluoromethyl substituent groups have similar directive effects towards the three electrophilic radicals. This is in sharp contrast to electrophilic ionic addition where, for... 

The effect on the coordination chemical shift of varying the phosphine has been studied for two series of trigonal metal-olefin complexes, viz., (CH2 CH2) PtL (46) and (CH2 C(CH3)C02C2H )NiL2 (49). In both cases the chemical shift is found to correlate with the basicity of the phosphine [Table IV (41, 45, 46, 49-52)]. The chemical shift of the unsubstituted olefinic carbon atom (CH2 ) of the ethyl methacrylate complexes is more strongly phosphine-dependent than the substituted olefinic carbon atom, and this effect has been attributed to electron withdrawal from this site by the ethoxycarbonyl substituent. 

The trends in the ozonolysis rates of simple olefins require further examination. The object of the present work was to obtain kinetic data on the reaction of ozone with simple alkyl-substituted ethylenes. The results will allow a discussion of the substituent effects on the reaction rates and of the mode of ozone attack on the carbon-carbon double bond. 

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