Addition to Conjugated Systems

In the same manner as described before, arenesulfonyl thiocyanates are able to show self-addition to conjugated systems yielding sulfones243,244. More important, however, is that reactions of selenosulfonates with unsaturated systems as well as with nucleophilic carbon have been proved. 

Addition to conjugated systems can also be accomplished by any of the other three mechanisms. In each case, there is competition between 1,2 and 1,4 addition. In the case of nucleophilic or free-radical attack, the intermediates are resonance hybrids and behave like the intermediate from electrophilic attack. Dienes can give 1,4 addition by a cyclic mechanism in this way ... 

Radical addition to conjugated systems is an important part of chain propagation reactions. The rate constants for addition of cyclohexyl radical to conjugated amides have been measured, and shown to be faster than addition to styrene. In additions to RCH=C(CN)2 systems, where the R group has a chiral center, the Felkin-Ahn rule (p. 148) is followed and the reaction proceeds with high selectivity. Addition of some radicals, such as (McsSijaSi-, is reversible and this can lead to poor selectivity or isomerization. ... 

Sulfonyl chlorides are added in the presence of copper(I)- or copper(II)-chloride exclusively however, mostly in the further presence of triethylamine hydrochloride especially in additions to conjugated systems . ... 

NUCLEOPHILIC ADDITION TO CONJUGATED SYSTEMS CONJUGATE ADDITION AND MICHAEL REACHONS... 

The following examples illustrate typical additions to conjugated systems. Although conjugate addition is more common, Gr pard reagents (see Section 7.6.2) and lithium aluminium hydride (see Section 7.5) are more likely to add directly to the carbonyl. 

When a new carbon-carbon bond is produced by nucleophilic addition to conjugated systems, the process is called Michael addition. The generalised process involves an a, b-unsaturated compound and a compound containing an active hydrogen attached to a carbon atom (e.g., malonic ester, acetoacetic ester, nitrocompounds, aldehydes, ketones etc.) These are condensed in the presence of a base. The overall reaction and its mechanism can be represented as follows ... 

Addition to conjugated systems can also be accomplished by any of the other three mechanisms. In each case there is competition between 1,2 and 1,4 addition. In the case of... 

The addition reactions take place at a carbon-carbon multiple bond, or carbon-hetero atom multiple bond. Because of this peculiarity, the addition reactions are not common as the first step in pyrolysis. The generation of double bonds during pyrolysis can, however, continue with addition reactions. The additions can be electrophilic, nucleophilic, involving free radicals, with a cyclic mechanism, or additions to conjugated systems such as Diels-Alder reaction. This type of reaction may explain, for example, the formation of benzene (or other aromatic hydrocarbons) following the radicalic elimination during the pyrolysis of alkanes. In these reactions, after the first step with the formation of unsaturated hydrocarbons, a Diels-Alder reaction may occur, followed by further hydrogen elimination ... 

For a discussion of addition to conjugated systems, see Allen in Gilman, Organic Chemistry, An Advanced Treatise, pp. 666-700, John Wiley and Sons, New York, 1943. 

Additions to conjugated systems are further facilitated by some of the features discussed previously e.g., additions to dienes" " and enynes" in the presence of transition-metal catalysts and additions to enynes containing a suitably placed intramolecular function such as hydroxyl. Although uncatalyzed intermolecular additions to alkynylsilanes are not yet demonstrated, additions are seen in the presence of a transition-metal catalysts" and intramolecular additions to alkynylsilane functions by suitably placed internal organomagnesium-halide functions are facile. ... 

Hydroboration of Alkenes Addition of Hydrogen Additions to Conjugated Systems Free-Radical Additions Polyethylene Oxidation of Alkenes A WORD ABOUT... Ethylene Raw Material and Plant Hormone... 

Additions to Conjugated Systems 3.15.a Electrophilic Additions to Conjugated Dienes... 

In one of these products, HBr has added to one of the two double bonds, and the other double bond is still present in its original position. We call this the product of 1,2-addition. The other product may at first seem unexpected. The hydrogen and bromine have added to carbon-1 and carbon-4 of the original diene, and a new double bond has appeared between carbon-2 and carbon-3. This process, known as 1,4-addition, is quite general for electrophilic additions to conjugated systems. How can we explain it ... 

Additions to Conjugated Systems. The reaction of TMSCF3 with a, 8-unsaturated aldehydes or ketones under fluoride activation affords almost exclusively the 1,2-addition products. " Moreover, the 1,4-addition pathway may also participate in some cases, and occurs predominantly in 2-perfluoroalkyl chromones and related systems (eq 22). A 1,6-addition process in a suitably substituted substrate has also been described. A more general method for the 1,4-addition of CF3 groups to different enones consisted in the prior complexa-tion of the carbonyl with a bulky Lewis acid [aluminum tris(2,6-diphenylphenoxide)]. ... 

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