Ionic processes

Simple nitroalkanes such as nitroethane, 1-nitropropane, or 2-nitropropane are generally bad electrophiles for the SN2 reactions.14 In contrast, nitro groups at allylic positions are readily displaced by thiolate ions (Eq. 7.13)15 or lithium dialkylcuprates (Eq. 7.14).16 

In 1982, a new reaction was reported by Tamura and Ono namely, allylic nitro compounds undergo replacement of the nitro group by various nucleophiles in the presence of a palladium (0) catalyst.17a b 18a b The details of these reactions are discussed in Ref. 2b here, only some typical examples are presented. Carbon, sulfur, nitrogen, and phosphorous centered nucleophiles replace the nitro groups at the allylic positions. The reaction of allylic nitro compounds with triphenylphosphine is applied to the highly stereoselective olefination of aldehydes (Eqs. 7.15-7.18).19 

Allyl acetates are more commonly used as electrophiles for the palladium-catalyzed allylic alkylation than allylic nitro compounds.20 However, the reaction of allylic nitro compounds has found wider applications. Allylic nitro compounds are readily available by nitration of alkenes. The regio- and stereoselective introduction of electrophiles and nucleophiles into alkenes is possible as outlined in Eq. 7.19. In fact, this strategy is applied to the synthesis of terpenoids.21 

The starting aUylic nitro compound is obtained by nitration of 2-methylpropene with NOz. Subsequent Michael addition to methyl vinyl ketone followed by Pd-cataly zed ally lie alkylation affords terpenoids. 

Recently, elegant synthesis of awft -MRS carbapenum has been reported. Sequential reaction of nitromethane via conjugate addition-elimination to a,P-unsaturated esters followed by Pd-catalyzed substitution of the resulting allyl nitro compound with the naphthosultam affords the allylation product which is an anti (Eq. 7.20).22 

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Gurney R W 1954 Ionic Processes in Solution (New York Dover)... 

Gurney, R.W. Ionic Processes in Solution McGraw-Hill New York, 1953 Chapters 5 and 6. (Dover, New York, reprint. 1962.)... 

The behavior of a polar dielectric in an electric field is of the same kind. If the dielectric, is exposed to an external electric field of intensity X, and this field is reduced in intensify by an amount SX, the temperature of the dielectric will not remain constant, unless a certain amount of heat enters the substance from outside, to compensate for the cooling which would otherwise occur. Alternatively, when the field is increased in intensity by an amount SX, we have the converse effect. In ionic solutions these effects are vciy important in any process which involves a change in the intensity of the ionic fields to which the solvent is exposed—that is to say, in almost all ionic processes. When, for example, ions are removed from a dilute solution, the portion of the solvent which was adjacent to each ion becomes free and no longer subject to the intense electric field of the ion. In the solution there is, therefore, for each ion removed, a cooling effect of the kind mentioned above. If the tempera-... 

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