Norbomadienes electrophilic addition

Protection of C—C double bonds. The olefinic ligand of this cationic complex can be exchanged when heated above 20° with an excess of certain other olefins. Nicholas has used this property for protection of C—C double bonds, since the olefins can be regenerated by treatment of the complex with sodium iodide in acetone. The method is particularly useful for selective protection of dienes and polyenes. For example, the complex of norbomadiene undergoes electrophilic additions without isomerization to nortricyclane derivatives (equation I). The complex coordinates selectively with the less substituted and/or... 

The stereochemistry of electrophilic addition to norbornenes and norbomadienes is very interesting" . As these reactions form on intermediate carbocations, there arises, just as for the solvolysis of 2-substituted norbornanes and norbornenes, the question of the nature of these ions — classical or nonclassical. The electrophilic addi-... 

The electrophilic addition to norbomenes, norbomadienes and benzonorboma-dienes clearly shows that these models make it rather difficult to choose among the three alternative hypotheses assuming intermediate formation of a classical ion, a nonclassical ion or the presence of a rapid equilibrium of classical ions. 

This concept has been nicely demonstrated in the electrophilic addition of norbomadiene-fused pyrazoles, the product distribution of which was dramatically effected by the electron donating ability of the substituent at N-1. Electron withdrawing substituents inhibited the Wagner-Meerwein rearrangement by destabilizing 47 and therefore resulted in a predominance of alkene addition products 49 and 50. Alternatively, in the absence of an... 

The electrophilic anti- 1,2-addition of the elements of MeSF to C=C has been achieved by a one-pot reaction of Me2S+-SMe BF4- and Et3N.3HF with various types of alkenes267. Markovnikov products arise from unsymmetrically substituted olefins. The reaction of 2,6-norbomadiene proceeds with exclusive exo-attack on one double bond followed by participation of the second double bond to give rise to two isomeric 3,5-disubstituted nortricyclanes267. By contrast, no transannular --participation has been observed with 1,5-cyclooctadiene. The reaction is believed to occur via the corresponding thiiranium species267. 

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