Selenolate ions

Stable hindered selenoketones222 are easily reduced to give selenolate ions with various reducing agents and oxidized by air to form diselenides (Scheme 39). 

The parent compounds, methylselenomethyllithium and phenylselenomethyllithium, are less reactive towards alkylating agents than their higher homologs. They require higher temperatures (-20 C instead of -78 C) for a reasonable reaction rate irrespective of whether ether or THF is used. Unfortunately they produce, along with the expected alkylated selenides, appreciable amounts of the selenide resulting from substitution of the alkyl halide by the selenolate ion (Scheme 8, entry a). Apparently, under these conditions, the selenoalkyllithiums are in equilibrium with methylene and lithium selenolates. This side reaction can be avoided if the reactions are performed in THF-HMPA, under which conditions alkylation proceeds at temperatures as low as -78 C (Scheme 8, compare entry b to a). In several cases HMPA aids the alkylation of ot-selenoalkyllithiums. For example HMPA has been used for the alkylation of 1-phenylseleno-l-hexyllithium, and also for 1-selenocyclopropyl- and 1-selenocyclobutyl-lithiums (Scheme 8, entries c and e). 

Aliphatic selenols do not have characteristic absorption maxima although the aliphatic selenolate ion absorbs in the range 243-253 nm with a rather intense absorption, log s 3.7 This is about 10 nm higher than the corresponding band observed for aliphatic thiolate ions (230-240 nm) ° Again, because of the facile oxidation of selenols to diselenides, UV-visible spectra of these molecules must be obtained under carefully controlled experimental conditions and results must be interpreted cautiously. This was clearly demonstrated when the spectrum of selenophenoF was later shown to be a spectrum of a mixture of selenophenol and diphenyl diselenide. ... 

The reactivity of the tellurolate ion is pecuhar, since the corresponding aryl selenolate gives only the disubstituted o-selenoxylenes, and sodium hydrogen telluride gives only poor yields. 

Structural studies suggest that when the active site selenocysteine group is in the reduced form TrxR displays a high reactivity toward metal ions [85, 86]. It is possible that gold(III) compounds such as auranofin exert their cytotoxic effects by causing direct mitochondrial damage through selective modification of the selenol... 

Selenocyanates produce selenols or diselenides upon either reduction (e g. with sodium borohydride) or hydrolysis (see Scheme 1). They undergo displacement of the cyanide ion by various nucleophiles and add to alkenes in a maimer similar to selenenyl halides (see equation 14), except that catalysis with Lewis acids is required in the case of unactivated alkenes. The selenocyanates are also popular reagents for the preparation of selenides from alcohols, and (8) from carboxylic acids, as indicated in Scheme 3. 

Bis(triphenylstannyl) selenide (56), which is prepared by the reaction of NaHSe with triphenylstannyl chloride [82,83], smoothly liberates a nucleophilic selenolate species with the aid of a fluoride ion [82]. The reaction conditions are neutral, producing the selenolate in a naked form. Therefore, in the reaction with halides, the corresponding symmetrical selenides are obtained in excellent yields without generating by-products (Scheme 42) [82]. When 56 is reacted... 

As well as thiol esters, selenol esters (1) frequently exhibit a high and selective reactivity toward nucleophiles, which is enhanced even further by activation with heavy ions or oxidizing agents. These properties make selenol esters valuable acyl transfer agents. This review deals with general methods for the synthesis of selenol esters and their reactivity as acyl transfer agents. Furthermore, selenoesters (2), isomeric compounds of selenol esters, and their derivatives selenoamides (3) are also described. These compounds show the characteristic reactivity based on the carbon-selenium double bond. 

Because of its acidity benzeneselenol gives phenylselenolate ions in fhe presence of bases such as MeLi (in EtgO) [13] and NaH (in THF) [14]. Sodium selenolate prepared by NaBH4 reduction of (PhSe)2 is believed to be a complex with triethyl borate... 

Selenocyanates (RSeCN), which are employed for the synthesis of selenides and selenoesters, are usually derived from selenenyl halides and cyanide ion (or silyl cyanate) [38 k, 40]. Alkylation of potassium selenolate (KSeCN) with alkyl halides is an alternative means of preparation of aliphatic selenocyanates (Scheme 15.13)... 

Nucleophilic attack of selenolate anions on the iminium ion complex, generated... 

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