Selenophenols

Benzeneselenol (phenylselenol, selenophenol) [645-96-5] M 157.1, b 57-59 /8mm, 71-72 /18mm, 84-86 /25mm, d 1.480, n 1.616. Dissolve in aq N NaOH, acidify with cone HCl and extract with Et20, dry over CaCl2, filter, evap on a steam bath and distil from a Claisen flask or through a short... 

The tetrameric zinc anion [Zn4(//-ScPh)r,(ScPh)4]2 has been structurally characterized as the first example of a Zn4Se4 adamantane cage-type structure.594 A further example was characterized by Bochmann and co-workers as part of a study of polymetallic zinc selenophenolates, in this case with chlorides replacing the terminal selenophenolates, [Zn4(/u-SePh)6Cl4]. Octameric zinc species were also characterized with either chloride or phosphine ligands resulting in anionic and neutral complexes respectively, [Zn8(/x-SePh)12Cl4]2 and Zn8(yu-SePh)12(SePh)2 (P Pr3)2.301... 

The contents of the flask are then poured upon 600 g. of cracked ice, and, with hand stirring, 75 ml. of hydrochloric acid (sp. gr. 1.18) is added. The cold mixture is now filtered through glass wool in an ordinary funnel into a 2-1. separatory funnel. The aqueous layer is separated and extracted once with 250 ml. of ether (Note 7). The combined extract and main product are dried over 30 g. of calcium chloride, the ether is removed on a steam bath, and the residue is distilled using a 500-ml. modified Claisen flask.6 The selenophenol is collected at 57-59°/8 mm. or 84-86°/25 mm. the yield is 43-54 g. (57-71%) (Notes 6 and 9 through 14). The product should be sealed at once in a glass vial (Note 8). 

Selenophenol has been prepared from selenium tetrachloride and benzene in the presence of anhydrous aluminum chloride,6 and by the procedure described,7 which is a development of Taboury s.8... 

Glyoxaline, 22, 65 Glyoxylic acid, phenyl-, 24, 16 Grignard reaction, f>-bromophenylsele-nophenol, 24, 91 -butylselenol, 24,91 3,12-dihjrdroxy-Bcr-choIanyldi-phenylcarbinol, 24, 41 l-hydroxy-l-phenyl-l,2,3,4-tetrahy-dronaphthalene, 24, 85 selenocresols, 24, 91 selenophenol, 24, 89 thiophenols, 24, 91 Guanidoacetic acid, 22, 59... 

The higher yields of selenophenol are favored by exclusion of air, rapid stirring, and. not too rapid addition of selenium. 

An alternative procedure is to extract the selenophenol by sodium hydroxide solution, and subsequently to acidify and extract the liberated substance. The yield of selenophenol is not improved by employing such a procedure, but it may be of value with some compounds. 

The selenophenol is water-white but rapidly turns yellow in contact with the air. 

This is a general reaction. It can be used for preparing other selenophenols whenever the desired Grignard reagent can be obtained. The submitter has made the three selenocresols, p-hromophen y 1 scl enophenol, and m-butylselenol by this procedure. He has also obtained thiophenols by the substitution of sulfur for selenium. 

The submitter has synthesized nine alkyl phenyl selenides in yields of 85-95% by treating alcohol solutions of the sodium salt (the selenophenol is dissolved in the calculated amount of 50% aqueous sodium hydroxide diluted with alcohol) with the appropriate alkyl halide or sulfate. 

Many selenophenols are more advantageously prepared by hydrolysis of the aryl sclcnocyanate. 

The 1,4-addition of selenophenols to cycloalkenones proceeds smoothly under the same conditions used in the thiophenol addition (see Section V) (eq. [18]). Although the e.e. of the products is 40 to 65%, compared with the 60 to 80% achieved in the thiol addition reaction, the solid adducts are readily purified to enantiomeric purity by crystallization (63). 

Although the mechanism of this reaction has not been studied as thoroughly as that of the thiol addition reaction, there appears to be considerable similarity in the main features of the reaction. Thus, although the transition state may well differ in a number of details, the transition state shown earlier (Figure 10) appears to predict the correct configuration for the products of the selenophenol addition as well as of the thiophenol addition to cyclohexenones. 

Asymmetric induction of the Michael addition of thiols to electron-deficient alkenes (4.6.1) has been achieved in high overall conversion using both free [e.g. 12-20] and polymer-supported [e.g. 21, 22] cinchona alkaloids and their salts [23-25], but with varying degrees of optical purity. The corresponding asymmetric Michael addition of selenophenols to cyclohex-2-enones is promoted by cinchoni-dine to give a chiral product (43% ee) [26],... 

The third method makes use of the one-flask procedure, which is advantageous from the preparative point of view. However, opening of certain stereoisomeric epoxides (263) with selenophenol suffers from low regioselectivity, resulting in a low yield of the final product. The other disadvantage is the basic reaction-medium occasioned by the method used for the generation of selenophenol, namely reduction of diphenyl diselenide with sodium borohydride in solution in anhydrous alcohol (see Ref. 356) some epoxides are sensitive to basic media. However, David (see Ref. 356) did not observe side reactions in his syntheses of 256. 

M(SR)5].624 The selenophenolates were formed by a similar procedure. Monomeric Nb(Et2dtc)3] has been prepared (equation 57) dimerization was observed in non-polar solvents in the presence of dithiocarbamates.593 Poorly characterized pyrrolidinedithiocarba-mate, [Nb(S2NC5Hs)3], has also been reported.625... 

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