Double bonds, nucleophilic addition

Nucleophilic substitution, electrophilic addition to the double bond, nucleophilic addition to the double bond in which atoms differ in their electronegativity, intramolecular conversions, and reduction are the most important reactions that may result in the appearance of asymmetric carbon atoms [41]. Unfortunately,... 

When both the carbonyl group and the sulfinyl group of a /J-ketosulfoxide are attached to the same carbon atom of a carbon-carbon double bond, then addition of nucleophiles can occur at the electrophilic -carbon atom (i.e., 1,4-addition, conjugate addition) and/or... 

Similar schemes can be developed easily for analogous reactions of acceptor-substituted polyenes. For example, a triene with an acceptor group in 1-position can form six regioi-someric products of Michael addition and electrophilic capture, and each of these exists as E/Z stereoisomers, diastereomers and/or enantiomers. Thus, reactions of this type are only useful if both the regio- and stereoselectivity can be controlled fortunately, only one isomeric Michael adduct is formed in many cases. This is true in particular for polyunsaturated Michael acceptors which bear at least one triple bond besides one or more double bonds. An additional feature of the latter substrate type is that nucleophilic additions can... 

Vinylation of dienes in the presence of piperidine or morpholine yields aminodienes as major products. Sometimes trienes are minor products. The reaction is believed to proceed by way of a ir-allylpal-ladium complex formed by addition of the vinylpalladium halide to the least-substituted diene double bond. Nucleophilic attack of the amine upon the ir-allylic complex gives the aminodienes, while hydridopalladium halide elimination yields trienes (Scheme 6).97... 

Palladium coordinates to one face of the diene promoting intramolecular attack by the alcohol on the opposite face. The resulting <7-alkyl palladium can form a 71-allyl complex with the palladium on the lower face simply by sliding along to interact with the double bond. Nucleophilic attack of chloride from the lithium salt then proceeds in the usual way on the face opposite palladium. The overall addition to the diene is therefore cis. 

Because the elementary reactions of cationic alkene polymerizations are directly related to the organic chemistry of carbocations, Chapter 2 will investigate electrophilic additions to double bonds, nucleophilic substitution, electrophilic aromatic substitution, and elimination reactions. 

In this light the results with diolefins do not appear surprising. In fact with the Pd(II)-carbon systems, also addition has recently been shown to be cis (Section IV, A). When Pd(II) is not 7r-complexed to the double bonds, the addition is cis-exo, and when Pd(II) is complexed in the endo position the addition is cis-endo. Another factor in the diene complexes is the fact two cis coordination positions are taken up. Since chloride may not be as readily displaced to give the nucleophile, attack may tend to be trans. Moreover these are neutral complexes and thus may be more susceptible to nucleophilic attack. 

Nucleophilic addition to the C-C double bond (Michael addition) is followed by ring closure with elimination of the sulfide (R2S). This reaction mode requires an electron-deficient alkene (typically a, 6-unsaturated carbonyl compounds and acrylonitriles) and represents an important synthetic method, see Section 1.1.1.1.2., and Houben-Weyl Vol. Ell, pl44ff. 

Triene 20, containing isolated and conjugated double bonds, underwent addition of two molecules of dichlorocarbene to the most nucleophilic sites to give dicyclopropane 21. ... 

The mercury derivatives of bicyclic and monocyclic cyclopropanes underwent ready addition across electron-deficient C —C double bonds. This addition reaction was performed with isolation of the mercury intermediate, e.g. 6, giving and often without isolation of the mercury intermediate giving and 9 directly. Depending on the solvent used (MeOH or HOAc) either methoxide or acetate acted as the nucleophile in the ring-opening reaction. 

A methyl group attached to the double bond should decrease the rate of the nucleophilic attack by increasing the electron density and the steric interactions at the double bond. In addition, an a-methyl group should decrease the overall rate even for highly basic nucleophiles, by blocking the elimination-addition route. Substituent effects in a-aryl-sulphonyl-j8-haloethylenes bear out this prediction. The rate retardation by an a-methyl group, more pronounced for the less reactive... 

What happens when p-hydrogcn elimination in the ruthenacyclic intermediate 45 is preduded, as in the case when vinyl ketones are the alkene partners (Equation 1.55) Given the extraordinary ability of Ru to interconvert easily among numerous oxidation states, one can imagine that the Ru can activate the double bond towards additions. For example, in the presence of water, protonation at the carbon (5 to Ru in the ruthenacyclopentene followed by nucleophilic addition of hydroxide can lead to 1,5-diketone formation. Indeed, terminal alkynes undergo smooth three-component coupling to form 1,5-diketones as shown in Equation 1.56 [52]. 

The Prins reaction with formaldehyde is a well-known route to prostaglandins using bicyclic lactone 3 as a precursor. One synthesis of this lactone14 started this sequence with a Prins reaction. Treatment of norbomadiene with paraformaldehyde in the presence of formic acid produced a mixture of epimeric diformates in 67% yield which were transformed in several steps into lactone 3. A second synthesis starts with the unsaturated bicyclic lactone which undergoes attack by the oxonium ion both regio- and stereoselectively from the less hindered face of the double bond, trims Addition of the nucleophilic acetate generates the lactone 3 as the bisacetate derivative15. 

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