4,4 -Dichlorodiphenyl diselenide

Olefin synthesis. The preparation of olefins by decomposition of alkyl phenyl selenoxides (Diphenyl diselenide, 5, 272-276) is very useful, except in the case of primary alkyl phenyl selenoxides, which usually give low yields of terminal olefins on decomposition. However, the presence of electron-withdrawing substituents on the benzene ring increases both the rate of elimination and the yield of olefins. In instances where use of diphenyl diselenide results in low yields. Sharpless and Young recommend use of o-nitrophenyl selenocyanate (1) or 4,4 -dichlorodiphenyl diselenide, both of which are converted into the corresponding ArSe Na" reagents on reduction with sodium borohydride in ethanol. 

The reagent Na Se"C6H4Cl(p) is nearly equivalent to Na Se C6H4N02(o) and has the advantage that 4,4 -dichlorodiphenyl diselenide is as easy to prepare as diphenyl diselenide (75% yield from p-bromochlorobenzene). 

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