Electrophilic Addition to Unsaturated Bonds

A series of selenenyl compounds - selenenic acids, selenenic anhydrides, selene-nyl halides, selenocyanates, and selenenamides, etc. - act as excellent electrophilic selenenylation reagents toward a variety of carbon-carbon unsaturated compounds. For example, electrophilic addition of selenenyl halides to carbon-carbon double bonds proceeds stereospecifically in the anti conformation. This addition is first-order in both selenenyl halides and carbon-carbon unsaturated compounds. 

With internal alkenes, a mixture of Markovnikov and anti-Markovnikov adducts is usually obtained [76, 77]. Interestingly, the addition of PhSeCl to allylic acetates proceeds with excellent regioselectivity even for internal alkenes [79]. This is probably because of coordination of the acetate group to the seleniranium ion. 

Selenenic acids generated in situ are also used for oxyselenation of a variety of 

The overall reactions thus provide a useful method for synthesis of allylic alcohols from alkenes. 

Synthesis of a, -Unsaturated Carbonyl Compounds via a-Seleno Carbonyl Compounds 

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