A convenient synthetic method has been developed for the preparation of unsymmetrical selenides through a one-pot zincmediated reaction of diselenides and active organic halides in aqueous media.
Two convenient rapid, efficient, stereoselective and highly regioselective methods for the synthesis of b-hydroxy selenides by the direct opening of epoxides with diselenides in acetonitrile in the presence of either Zn/AlCl 3 or zinc powder in aqueous sodium hydroxide solution are described. These methods appear to be competitive with the other methods previously reported.b-Hydroxy selenides are valuable selenium intermediates in organic synthesis; 1 they can be converted to allylic alcohols, olefins, bromohydrins, vinyl selenides and epoxides. 2-5 Several methods are available for the preparation of b-hydroxy selenides. These hydroxy compounds have been found as the addition products of selenenic acids to olefins with a good regioselectivity. 6 The S N 2 displacement of bromine from b-bromoselenides by hydroxide ion is another stereoselective method. 7 The alkaline hydrolysis of b-acetoxyselenides has been described. 8 A convenient method for the synthesis of b-hydroxy selenide uses N-phenylselenophthalimide (NPSP) in the presence of water. 9 Another important method is the reaction of aldehydes and ketones with seleniumstabilized carbanions. 10 The reduction 11 or nucleophilic addition of Grignard reagents, 11 alkyllithium, a-selenoalkyllithiums 12 to a-selenoaldehydes or b-selenoketones provide other methods for access to b-hydroxy selenides.The S N 2 ring-opening of epoxides, using selenolate anions, is a common method for preparing b-hydroxy selenides. This method provides an excellent preparative route to allylic alcohols via selenoxide elimination. 2 Other effective reagents for epoxide-opening include phenyl trimethylsilyl selenide, 13 aluminum selenolates, 14 selenoboranes, 15 and benzeneselenol in the presence of alumina. 16 Attack by the selenolates generally occurs at the less hindered epoxide carbon and is anti stereospecific. In cyclic systems, a strong preference for approach from the axial direction may outweigh other factors.Herein, we report that alkyl and arylselenide ions can be easily generated from the corresponding diselenides in the presence of either Zn/AlCl 3 under neutral conditions or with zinc powder in aqueous sodium hydroxide solution.The anion can then react, under mild and atmospheric conditions, with different classes of epoxides to give bhydroxy selenides, formed via trans-opening of the epoxides, in moderate to excellent yields (Scheme 1). Table 1 shows the results obtained in the reactions of a series of representative epoxides with diphenyl-and dibenzyl diselenides in the presence of Zn/AlCl 3 system in anhydrous acetonitrile (method A), compared with the results obtained in the presence of zinc powder and aqueous sodium hydroxide in acetonitrile (method B).
Scheme 1From the results in Table 1 it is quite evident that, in the case of unsymmetrical epoxides, the reaction proceeds with a remarkable regioselectivity because in most cases selenolate anions exclusively attack the less hindered carbon of the epoxide to give the regioisomer (2, Scheme 1). The exceptions are given b...
Selenol esters were prepared in good yields by reacting diselenides with carboxylic acid anhydrides in dry acetonitrile in the presence of a Zn/AlCl 3 system.
Organo-selenium compounds
Organo-selenium compounds S 0130Reductive Cleavage of the Se-Se Bond in the Presence of a Zn/AlCl 3 System: Synthesis of Selenol Esters. -(MOVASSAGH*, B.; SHAMSIPOOR, M.; JOSHAGHANI, M.; J.
Organo-selenium compounds S 0130 Stereo-and Regioselective Zinc-Mediated Ring-Opening of Epoxides with Diselenides. -A new method is described for in situ formation of zinc selenides. Their reaction with epoxides affords β-hydroxy selenides in good yields. -(MOVASSAGH*, B.; SHAMSIPOOR, M.; Synlett 2005, 8, 1316-1318; Dep. Chem., K. N. Toosi Univ. Technol., Tehran, Iran; Eng.) -Mais 41-179
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