Benzeneselenenyl chloride alkenes

It has been found that selenium electrophiles add to electron-deficient alkenes to form mixtures of adducts. Benzeneselenenyl chloride adds to chlorocyclohexene (17), producing a mixture of adducts (equation 13). 1,1-Difluoroethylene furnishes only one regioisomer (equation 14). Benzeneselenenyl... 

Benzeneselenenyl chloride adds to alkynes to produce mixtures of trans-alkene adducts. For example, the addition of benzeneselenenyl chloride to the alkyne (18) produces the alkene (19), which can be transformed to yield the unusual diene (20 equation 16). Alkynic alcohols give anti-Miukovnikov addition products under kinetic control. The reaction is thought to proceed dirough the selenirenium ion (21 equation 17). Selenium electrophiles add to a, -alkynic caibonyl moieties to produce cis adducts in good yield (equation 18). ... 

Benzeneselenenyl azide adds to alkenes readily. The addition of the selenenyl azide always occurs with trans stereochemistry. The yield of adducts is reliably high with several different alkenes. Unlike benzeneselenenyl chloride, mixtures of regioisomers are found with simple primary alkenes. No addition occurs between benzeneselenenyl azide and ethyl crotonate. The reagent adds to conjugated dienes in a trans 1,4-fashion which is thought to be due to an initial trans 1,2-addition, followed by a facile 1,3-allylic azide shift (equation 19). Unfortunately, this reagent must be prepared and used in situ ... 

Heterocycles can be prepared from selenium-induced cyclizations of urethanes, thioesters and alkenes. These cyclizations are seen infrequently, but have much potential in heterocyclic synthesis. The aniline (37) was treated with benzeneselenenyl chloride and silica gel (to facilitate the ring closure) to produce the hexahydrocarbazole (38) in good yield (equation 30). Sulto heterocycles are prepared similarly to nitrogen heterocycles. ... 

Selenium and tellurium reagents have been used for stereoselective halogenations of alkenes. For example, trans addition of benzeneselenenyl chloride to alkenes followed by the displacement of the seleno moie with chloride can lead to dr-1,2-dichlorides (equation 25). The addition of 2-naph-thyltellurium trichloride proceeds in an anti stereospecific manner (equation 26), whereas tellurium tetra-diloride gives a mixture of syn and anti adducts. The reaction of allyl esters with tellurium tetrachloride accompanies acyl migration to give the l-(trichloiottlluro)-3-chk>io adduct (54 equation 27). ... 

More recently, these concepts have been extended to include a range of elegant amidoselenation processes. Alkenes react with benzeneselenenyl chloride and nitriles to yield 3-amido phenyl selenides in excellent yield. - Oxidative elimination of the latter provides the corresponding allylic amides (Scheme 60). Since the reaction proceeds via an episelenonium intermediate, Ae amido selenides are formed with tram stereospecificity. However, when applied to nonsymmetrical alkenes (equation 50) it only proceeds with regioselectivity. 

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