Selenophilic attack

Steric protection by the bulky 2,4,6-tri-f-butylphenyl (TTBP) group of the selenium atom in the episelenonium ion intermediate (17), generated in situ from (16), has been utilized in the selective formation of carbocyclic compounds (17)—>(19)—>(20) and (21)—>(22). The selenophilic attack (17)—>(18), leading to isomerization, can thus be avoided (Scheme 8).33... 

The reaction of the lithiated allylic carbanion derived from prenyl selenide with hexamethyldistannane did not lead to the mono a-stannylated allylic selenide but to a bis-stannylated compound. A consecutive Se/Sn exchange, without allylic isomerization, occurred [5] (Scheme 4). The reaction involves a selenophilic attack by Mej SnLi formed in the media. 

HMPA as cosolvent, the nature of the electrophilic reagent and the reaction time and temperature [60] (Scheme 46). It was discovered that the major side products formed besides the expected 2-phenylselanylalkanenitrile are bis(phenyl-selanyl)acetonitrile and propionitrile. The authors have proposed that the formation of bis(phenylselanyl)acetonitrile would result from the decomposition of an ate complex, the latter being formed by selenophilic attack of the carbanion derived from phenylselanylacetonitrile on the substrate. The a-selanyl nitriles behave as a-phenylselanyl ketones when treated with bases. 

The formation of 86 was explained in terms of the selenophilic attack of R R P(OMe) giving 88, followed by elimination of the selenium atom to yield 89, protonation of which provided 86. On the other hand, the formation of 87 was rationalized by the carbophilic attack of R R P(OMe) to produce 90 followed by Me-migration to afford 91, and the elimination of R R P(OH) which furnished 87 [25a]. 

One of the main properties of selenides is their aptitude for attack by various nucleophilic reagents. Alkyllithiums, which are not reactive with sulfides, have a marked selenophilic character. They form an ate complex on the selenium atom, which immediately decomposes with cleavage of one C-Se bond leading to the more stable carbanionic species. 

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