Alkenes conjugation effects

Iron phthalocyanine catalysis is more effective for alkenes conjugated to an aryl ring as compared with the Fe2+/Fe3+ salts (Scheme 3.34), whereas the Nicholas method worked much better for acyclic non-conjugated alkenes such as li (Scheme 3.35). 

The conformational problems of cyclohexene derivatives are somewhat different than those observed with cyclohexanone or cyclohexane derivatives. The presence of the alkene moiety effectively flattens four carbons of the ring, which changes the different steric effects for substituents with an incoming reagent, relative to cyclohexanone derivatives. The most abundant conformations of cyclohexenone derivatives are 310 and 311. The first problem that arises in conjugated derivatives is the competition of 1,2- with 1,4-addition for... 

A physical interpretation has been ascribed to each of the three terms in the MM2 torsional expansion from an analysis of ab initio calculations on simple fluorinated hydrocarbons. The first, onefold term corresponds to interactions between bond dipoles, which are due to differences in electronegativity between bonded atoms. The twofold term is due to the effects of hyperconjugation (in alkanes) and conjugation effects (in alkenes), which provide double bond character to the bond. The threefold term corresponds to steric interactions between the 1,4 atoms. It was found that the additional terms in the torsional potential were especially important for systems containing heteroatoms, such as the halogenated hydrocarbons and molecules containing CCOC and CCNC fragments. 

The effect of the solvent on the product distribution is observed in the conjugate addition of amines to 1-bromo-l-(phenylsulfonyl)alkenes (54) (equation 54)46. When the reaction is conducted in benzene at room temperature for 4 days, the adduct 55 is formed in good yield. On the other hand, the reaction in DMSO at 80-90 °C for 2.5 h affords 2-(phenylsulfonyl)aziridines (56) and no adduct (55) is isolated. 

Isomerization of ( /Z) isomers is another important transformation. Isomerization of ( ) and (Z-) conjugated amides is effected photochemically " (photo-isomerization " ). There is a rather high energy barrier for the excited state required for (E/Z) isomerization. Isomerization of the C=C units in dienes is also induced photochemically. " Isomerization of cyclic alkenes is more difficult but cyclooctene is isomerized photochemically. " Conjugated aldehydes have been isomerized... 

Conditions for effecting conjugate addition of neutral enolate equivalents such as silyl enol ethers in the presence of Lewis acids have been developed and are called Mukaiyama-Michael reactions. Trimethylsilyl enol ethers can be caused to react with electrophilic alkenes by use of TiCl4. These reactions proceed rapidly even at -78° C.308... 

The structure-activity relation of triterpene QMs on the anti-inflammatory effect has been investigated with a series of analogues by comparing inhibition of the IL-1 (3 production in the LPS-induced monocytes.93-94 Clearly, the conjugated QM structure with alkenes is essential for the observed inhibition, and similar inhibitory effect was found with derivatives that are capable to form the conjugated QM through hydrolysis and/or oxidation.93-94 Also, the presence of the E ring in the triterpene QM structure is an additional contributor. 

An extended form of (39) has been used to analyse kinetic substituent effects on bromination of alkenes GRaC=CR()R) , where G is a conjugatively electron-donating group and R is alkyl (Bienvenue-Goetz and Dubois, 1981). 

Bromination rates of aliphatic enol ethers have been included in the interactive treatment of alkenes GRIC=CR R, with G being a conjugated group most of them fit the multiparameter equation (41) satisfactorily. A more detailed analysis of reactivity-selectivity effects in the reaction of 1-ethoxyethylene [22] and its a- and / -methyl analogues [23] and [24] has been carried out,... 

This result, associated with those on substituent effects, supports previous conclusions to the effect that the position of the transition state depends on the reactivity in agreement with RSP. In particular, stabilization of the intermediate as a result of conjugation, such as that in the reaction of enol ethers, makes the transition state very early. The few available KSIEs also suggest that the transition states for aromatic series are earlier than those for alkenes. 

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