O-Nitrophenyl selenocyanate

Alcohols can be converted to o-nitrophenylselenides by reaction with o-nitrophenyl selenocyanate and tri( -butyl)phosphine.329... 

Olefin synthesis from the 5yn-oxidative elimination of o-nitrophenyl selenides, which may be prepared using o-nitrophenyl selenocyanate and BU3P, among other methods. 

The best method of preparation, however, is as follows 2 9 1 grams of aniline in dilute sulphuric acid (1 4) are diazotised at 3° C. with 9 5 grams of sodium nitrite and the solution, made neutral to Congo paper with sodium acetate, is added to a cold aqueous solution of 22 grams of potassium selenocyanate. After fifteen hours steam distillation gives a pale yellow oil, which, when dried over calcium chloride, boils at 134° C. at 10 mm. and at about 250° C. with decomposition at ordinary pressures. The yield is about 50 per cent. When nitrated at -5° C. with nitric acid (density 1 5), p-nitrophenyl selenocyanate and a very small amount of o-nitrophenyl selenocyanate are obtained. p-Chlorophenyl selenocyanate,... 

A. Krief, A.-M. Laval, o-Nitrophenyl Selenocyanate, a Valuable Reagent in Organic Synthesis Application to One of the Most Powerful Routes to Terminal Olefins from Primary-Alcohols (The Grieco-Sharpless Olefination Reaction) and to the Regioselective Isomerization of Allyl Alcohols, Bull. Soc. Chim. Fr. 1997,134, 869-874. 

Another useful system is o-nitrophenyl selenocyanate and tributylphos-phine (Bu3P), developed by Grieco and co-workers,104-106 which has been employed in the synthesis of intermediates leading to the ionophone antibiotic calcimycin.103... 

Reaction of alcohol 4.12 with o-nitrophenyl selenocyanate (4.13) and tributylphosphine gives 4.14. Oxidation of 4.14 with hydrogen peroxide gives selenoxide 4.15. Aryl selenoxide 4.15 bearing a (3-hydrogen atom is unstable and undergoes thermal syn-elimination to give styrene (4.16) with the expulsion of a selenol 4.17 in a fashion similar to that of the Cope elimination (Scheme 4.13). 

Benzoselenazole-2-thione 63 is obtained by a four-step procedure starting from o-nitroaniline <2002J(P1)1568, 2001CC1336>. Reaction of potassium selenocyanate with the diazonium salt yields o-nitrophenyl selenocyanate. Treatment of the o-nitrophenyl selenocyanate with sodium in ethanol affords bis(o-nitrophenyl) diselenide. The m situ reduction of this with sodium hydrosulfide gives an intermediate o-aminobenzeneselenoate, which cyclizes with carbon disulfide in basic medium, work-up giving 3/7-benzoselenazole-2-thione 63 (Scheme 22). 

KETONES Bis(phenylthio)methane. Chlorothexylborane. Grignard reagents. Nickel chloride-Zinc. o-Nitrophenyl selenocyanate. Organomagnesium(II) iodides. PhcnylthiophenyKtrimethyl-silyDmcthanc. 

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. 

SELENOXIDE ELIMINATION r-Butyl hydroperoxide. o-Nitrophenyl selenocyanate. 

The process using o-nitrophenyl selenocyanate was described by Clive (1978) and has been elaborated upon as described by Reich (1979). 

Scheme 8.74. The formation of a terminal alkene by an elimination reaction sequence that begins with the conversion of the oxygen of cyclohexylmethanol to a good leaving group through a reaction with tri- -butylphosphine and o-nitrophenyl selenocyanate to form the corresponding selenide (where the oxygen of the starting alcohol has been replaced with the aryl-substituted selenium). Subsequent oxidation to a selenoxide is followed by a rapid elimination to the desired alkene (methylenecyclohexane).

Alcohols can be converted to o-nitrophenylselenides by reaction with o nitrophenyl selenocyanate and tri(rt-butylphosphine). Several oxidants have been employed to convert selenides to selenoxides and bring about elimination. Hydrogen peroxide, sodium metaperiodate, peroxycarboxylic acids, tert bnty hydroperoxide, and ozone have been used most frequently. 

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