Stereo- and Regioselective Zinc-Mediated Ring-Opening of Epoxides with Diselenides

Abstract

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...

Ring opening reactions of heterocycles with selenium and tellurium nucleophiles

“…In situ reaction of the so generated zinc selenolates with epoxides afforded β-hydroxy selenides in high yields with good regioselectivity. 14 Santi, Tiecco and co-workers reported an efficient zinc-mediated reduction of diselenides into the corresponding selenols, occurring in a biphasic system under acidic conditions (Scheme 4). 15 Selenols generated under these conditions react in situ with epoxides, enabling the synthesis of β-hydroxy selenides.…”

New Catalytic Method for the Synthesis of β‐Hydroxy Selenides

“…Using selenolate anions, the S N 2 ring opening of epoxides is another common method for access to β ‐hydroxy selenides. The selenolate anions can be generated by the treatment of diphenyl diselenide with Na, Zn, NaBH 4 , zinc/aluminum (III) chloride, tributylphosphine in an alkaline medium and sodium hydroxymethanesulfinate . They are also transformed from benzeneselenol under supramolecular catalysis in the presence of β ‐cyclodextrin and promoted by [Bmim]BF 4 .…”

Ultrasound Assisted Ring-Opening Reaction of Epoxides with 1,2-DiphenylDiselenide

“…These promoting agents include Sm-TMSCl, 8 ytterbium(III) chalcogenolate complexes, 9 NaBH 4 /NaOH under microwave irradiation, 10 tetrathiomolybdate, 11 indium compounds, 12,13 PBu 3 , 14,15 and zinc compounds. 16,17 Recently, Chen and co-worker reported that Rongalite ® -promoted highly regioselective synthesis of β-hydroxyselenides by grinding under solvent-free conditions, 18 which could not be applied to large-scale synthetic procedures with a glass pestle in the glass mortar using manual labour. Also, when treated with a base Rongalite ® readily decomposes into the toxic formaldehyde.…”