Reagents selenium

For the reagents used to effect /J-hydroxyselenide elimination, see page 286, Section 34. 

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In spite of the hazardous nature of Sc4N4, this binary selenium nitride has been used for the synthesis of other Se-N compounds, all of which have sulfur analogues (Scheme 5.2). " However, safer alternatives to the use of Sc4N4, e.g., selenium-nitrogen halides and silicon-nitrogen-selenium reagents, are available for the development of Se-N chemistry. ... 

For reviews of selenylations, see Back, T.G. in Liotta Organoselenium Chemistry, Wiley NY, 1987, p. 1 Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis Pergamon Elmsford, NY, 1986, p. 95. 

PAULMIER Selenium Reagents Intermediates in Organic Synthesis... 

Addition Reactions with Electrophilic Sulfur and Selenium Reagents... 

Scheme 4.3. Sulfur and Selenium Reagents for Electrophilic Addition Reactions...

Various electrophilic selenium reagents such as those described in Scheme 4.3 can be used. V-Phenylselenylphthalimide is an excellent reagent for this process and permits the formation of large ring lactones." The advantage of the reagent in this particular application is the low nucleophilicity of phthalimide, which does not compete with the remote internal nucleophile. The reaction of phenylselenenyl chloride or V-phenylselenenylphthalimide with unsaturated alcohols leads to formation of (3-phenylselenenyl ethers. 

Alkynes react with electrophilic selenium reagents such as phenylselenenyl tosylate.155 The reaction occurs with anti stereoselectivity. Aryl-substituted alkynes are regioselective, but alkyl-substituted alkynes are not. 

C. Paulmier, Selenium Reagents and Intermediates in Organic Synthesis, Pergamon, Oxford, 1986. 

This reaction depends upon the facile solvolysis of (J-haloselenides and the facile oxidative elimination of a selenoxide, which was discussed in Section 6.6.3. An alternative method, which is experimentally simpler, involves reaction of alkenes with a mixture of diphenyl diselenide and phenylseleninic acid.189 The two selenium reagents generate an electrophilic selenium species, phenylselenenic acid, PhSeOH. 

For books, see (a) C. Paulmier, Selenium Reagents and Intermediates in Organic Synthesis, Pergamon Press, Oxford, 1986 (b) S. Patai and Z. Rappoport (eds), The Chemistry of Organic Selenium and Tellurium Compounds, vol 2, Wiley, New York, 1987. 

There are also immobilized versions of selenium reagents (Scheme 2.6), which are not only stable to the air, but have no odor, unlike the pungent solution phase equivalents [18]. 

Recently, the semi-synthesis of Vancomycin (48) on solid supports was accomplished using an allylic linker (Scheme 3.2) [123, 124]. Polymer-bound chiral electrophilic selenium reagents have been developed and applied to stereoselective se-lenylation reactions of various alkenes (Tab. 3.9) [125]. 

In many synthetic applications, the sulfur or selenium substituent is subsequently removed by elimination, as will be discussed in Chapter 6. Arenesulfenyl halides, ArSCl, are the most commonly used of the sulfur reagents. A variety of electrophilic selenium reagents have been employed, and several examples are given in Scheme 4.3. 

Electrophilic selenium reagents are very effective in promoting cyclization of unsaturated molecules containing potentially nucleophilic substituents.72 Unsaturated carboxylic acids, for example, give selenolactones, and this reaction has been termed selenolactonization73 ... 

Sulphuric acid-selenium reagent, approx 98% m/m H SO - Safety note wear PPE because this is highly corrosive. Add 4 g selenium powder to 400 ml sulphuric acid (approx. 98% m/m H SO ), and heat until just fuming. Stir occasionally with a glass rod until all the selenium has dissolved to give a dark green solution. Carefully remove from the hotplate and allow to cool. Make up to approximately 1 I with sulphuric acid. 

Allyl amides (enamides), for example, 225, 228, and 230 cyclize to oxazolines, for example, 226, 229, and 231 when the double bond is activated by an electrophile. The double bond can also be conjugated to a ketone, or present as an allylic epoxide. Reagents commonly used to promote the cyclization include acids,iodine,selenium reagents,and trimethylsilyl triflate (Scheme 8.63). ... 

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