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Selenocarboxylic acids [RC(=O)SeH] were found to readily react with aryl, acyl, and arenesulfonyl isocyanates to give the corresponding acyl carbamoyl selenides 3 [RC(=O)SeC(=O)NHR′, R′ = aryl, C6H5CO, and 4-MeC6H4SO2] in good yields. Their tautomers [RC(=O)SeC(=NR′)OH] were also detected by 1H, 13C, and 77Se NMR spectroscopies. The structure of 3 [R = 2,6-(MeO)2C6H3, R′ = 4-MeC6H4] was characterized by X-ray crystallography, which showed that this molecule is stabilized by an intramolecular hydrogen bond between the carbonyl oxygen and the NH hydrogen to form a planar six-membered ring and by nonbonded interaction of the ortho methoxy oxygen with the carbonyl oxygen or the selenium atoms. 4-Methoxybenzoyl and 4-methoxythiobenzoyl N-(4-methylphenyl)carbamoyl sulfides (4 and 5) were shown by X-ray crystallography to similarly have a planar intramolecular six-membered ring formed by a hydrogen bond between the carbonyl oxygen or thiocarbonyl sulfur and NH hydrogen atoms. The tautomers [RC(=E)SC(=NR′)OH; E = O or S] of 4 and 5 also were detected spectroscopically. The reactions of 3h (R = 4-MeOC6H4, R′ = Ph) with sodium methoxide and p-toluidine gave sodium selenocarboxylate and the corresponding amides and urea as main products, respectively. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:250–258, 2001

Bis(phosphine)bis(tellurocarboxylato)-palladium(II) and -platinum(II), [M(RCOTe)2(PR′3)2] (M = Pd or Pt; R = But, Ph, 4-MeC6H4, etc.; R′ = Et or Ph), were synthesized in moderate to good yields by treating sodium tellurocarboxylates or O-trimethylsilyl telluroesters with [MCl2(PR′3)2]. The platinum complexes with 2-methoxybenzenecarbotelluroato ligands also were synthesized from [Pt(PR′3)4] with the corresponding diacyl ditelluride. The tellurocarboxylato complexes are yellow to orange or red crystals, and labile thermally and toward oxygen. The nickel analogues [Ni(RCOTe)2(PR′3)2] (R′ = Et or Ph) were obtained by similar fashion, but were too labile to isolate. X-Ray diffraction analysis of trans-[Pt(4-MeC6H4COTe)2(PEt3)2] was carried out, and compared with those of the corresponding thio- and seleno-carboxylato complexes. These complexes crystallized in the same space group (P21/c) and are isostructural having a square-planar co-ordination geometry with thio- or telluro-carboxylato ligands which are unidentate.

The reaction of lithium alkyneselenolates generated from terminal acetylenes with thiols gave rise to lithium eneselenolates with high stereoselectivity. The trapping with alkyl halides afforded ketene selenothioacetals, whereas the trapping with allylic bromides yielded γ,δ-unsaturated selenothioesters via seleno-Claisen rearrangement.

Thiocarboxylic acids, such as selenocarboxylic acids, exist predominantly in the thioxo form (RCSOH, thion acid) in polar solvents such as tetrahydrofuran (THF) at temperatures below −50 °C. Tellurocarboxylic acids (5) were observed for the first time by acidolysis of the corresponding cesium tellurocarboxylates with hydrogen chloride. The telluroic acids (6) exist predominantly in the telluroxo form (RCTeOH, telluron acid) in THF at temperatures below −70 °C. Telluron acids were reddish to blue violet for the aliphatics (R = alkyl) and dark green for the aromatics (R = aryl) and reacted with aryl isocyanates at −70 °C to give crystalline acyl carbamoyl tellurides in good yields.

Aromatic diselenoic acid Se-methyl esters 1 react with amines at 0°C in tetrahydrofuran (THF) to yield selenoamides in moderate to good yields. The reaction course is highly dependent on the steric requirements of both starting materials. In the reactions of the ester 1a with 2-methylpiperidine and of the ester 1b with piperidine, the starting materials disappear within 1 hour with the liberation of black selenium, but the corresponding selenoamides are not produced. These results may be ascribed to the steric congestion caused by the formation of the selenoamide group from the tetrahedral intermediate 15. X-ray crystal structure analyses of the selenoamides 3 and 9 have been performed. The bond length of C(Se)N is shorter than a carbon nitrogen single bond. On the other hand, the CSe bond is longer than that of the ordinary carbon-selenium double bond. These results are indicative of the efficient delocalization of the electrons of nitrogen to the carbon–selenium double bond. The double bond character between the carbon attached to selenium and the nitrogen is also supported by the nitrogen atom showing sp2 character. When a methyl group is introduced at the meta position of the aromatic ring, the deviation of the aromatic ring from the plane involving the carbon–selenium double bond and nitrogen atom becomes substantially large, perhaps due to the steric bulkiness of the selenium atom.

Lithium 1-alkoxyeneselenolates 2 in tetrahydrofuran were characterized by 1 H NMR for the first time. Their reaction with propargyl bromide was found to proceed through a propargylic rearrangement to generate allenic selenoic acid O -esters 3 , which led to poly-substituted selenophenes in moderate yields under reflux.

A variety of allyl- and benzyllithiums were prepared by lithium-tellurium exchange reactions of allylic and benzylic tellurides generated in situ from the corresponding halides. The produced organolithiums were trapped successfully with electrophiles such as aldehydes, ketones, and trimethylchlorosilane. Benzyllithiums having an alkyl, alkoxy, fluoro, chloro, or cyano substituent(s) on their aromatic ring were generated efficiently in THF. Benzylic tellurides bearing a bromo or iodo substituent afforded a mixture of products under similar conditions arising from the competing lithium-halogen exchange and/or the displacement of the halogen atom with organolithiums used, but they were converted selectively to benzyllithiums in ether without affecting halogen substituents on the benzene ring. Several allyllithiums including dilithioisobutene were generated from allylic halides in a similar way via allylic tellurides. Wurtz-type coupling was negligible in any reactions examined.

Sodium selenocarboxylates were found to react with organoarsanyl chlorides Ph 3-n AsCl n 1-3 (n=1, 2, 3) to give the corresponding Se-organoarsanyl esters RCOSeAsPh 2 (5), (RCOSe) 2 AsPh (6) and (RCOSe) 3 As (7) in good yields. The reaction of Se-dipbenylarsanyl 4-methylbenzenecarboselenoate 5g with phenylselenenyl bromide and phenyltellurenyl iodide afforded the corresponding 5e-phenylselenenyl 13 and Se-phenyltellurenyl esters 14 in moderate yields, while the reaction with sodium phenoxide gave sodium 4-methylbenzenecarboselenoate (4g), phenyl 4-methylbenzoate (11) and phenoxydiphenylarsine (12), indicating the attack of phenoxy anion to both the carbonyl carbon and arsenic atoms

Acylselenenyl halides 2(X = Cl, Br) have been generated from RC(O)SeAsPh21 and N-halogenosuccinimide, and the chlorides 2(X = Cl) have been treated with enol silyl ethers to give Se-β-oxoalkyl Selenoesters 5 in good yields.

Aromatic diselenoic acid Se-methyl esters 1 react with amines at 0°C in tetrahydrofuran (THF) to yield selenoamides in moderate to good yields. The reaction course is highly dependent on the steric requirements of both starting materials. In the reactions of the ester 1a with 2-methylpiperidine and of the ester 1b with piperidine, the starting materials disappear within 1 hour with the liberation of black selenium, but the corresponding selenoamides are not produced. These results may be ascribed to the steric congestion caused by the formation of the selenoamide group from the tetrahedral intermediate 15. X-ray crystal structure analyses of the selenoamides 3 and 9 have been performed. The bond length of C(Se)N is shorter than a carbon nitrogen single bond. On the other hand, the CSe bond is longer than that of the ordinary carbon-selenium double bond. These results are indicative of the efficient delocalization of the electrons of nitrogen to the carbon–selenium double bond. The double bond character between the carbon attached to selenium and the nitrogen is also supported by the nitrogen atom showing sp2 character. When a methyl group is introduced at the meta position of the aromatic ring, the deviation of the aromatic ring from the plane involving the carbon–selenium double bond and nitrogen atom becomes substantially large, perhaps due to the steric bulkiness of the selenium atom.

Allylations of selenothioic acid S-alkyl esters with allylic bromides in the presence of Et3N in THF took place selectively at the α-position of selenocarbonyl group to give allylated products with high regio- and stereo-selectivity.

The reaction of lithium alkyneselenolates generated from terminal acetylenes with thiols gave rise to lithium eneselenolates with high stereoselectivity. The trapping with alkyl halides afforded ketene selenothioacetals, whereas the trapping with allylic bromides yielded γ,δ-unsaturated selenothioesters via seleno-Claisen rearrangement.

Thiocarboxylic acids, such as selenocarboxylic acids, exist predominantly in the thioxo form (RCSOH, thion acid) in polar solvents such as tetrahydrofuran (THF) at temperatures below −50 °C. Tellurocarboxylic acids (5) were observed for the first time by acidolysis of the corresponding cesium tellurocarboxylates with hydrogen chloride. The telluroic acids (6) exist predominantly in the telluroxo form (RCTeOH, telluron acid) in THF at temperatures below −70 °C. Telluron acids were reddish to blue violet for the aliphatics (R = alkyl) and dark green for the aromatics (R = aryl) and reacted with aryl isocyanates at −70 °C to give crystalline acyl carbamoyl tellurides in good yields.

α,α-Disubstituted selenoamides are synthesized from terminal acetylenes, selenium, amines and allylic bromides in good to high yields; their reduction with LiAlH4 affords alkenylamines quantitatively.

Reductive cyclization of γ,δ-unsaturated selenothioic acid S-esters with NaBH4 or LiAlH4 proceeds viaδ,Iµ-unsaturated selenols to afford tetrahydroselenophenes in good to high yields.

Novel water-soluble diaryl tellurides, alkyl aryl tellurides, and dialkyl tellurides carrying sulfopropyl groups were prepared and found to possess potent peroxide decomposing and chain-breaking antioxidative capacity. The dilithium, disodium, dipotassium, and bis-tetramethylammonium salts of bis(4-hydroxyphenyl) telluride (4) were treated with 2.3 equiv of 1,3-propanesultone in aqueous tert-butyl alcohol to give the corresponding salts 5 of bis-O-sulfopropylated diaryl telluride. A variety of diaryl ditellurides were reduced with sodium borohydride in ethanol. Upon addition of propanesultone to the resulting sodium arenetellurolates, the corresponding 3-aryltellurenylpropanesulfonic acid sodium salts 8 were precipitated. Diphenyl diselenide and dibutyl ditelluride reacted similarly to afford the sodium salts of 3-benzeneselenenylpropanesulfonic acid (9) and 4-telluraoctanesulfonic acid (10), respectively. The glutathione peroxidase-like activity of the water-soluble compounds was assessed at pH = 7.4 by ...

Selenocarboxylic acids [RC(=O)SeH] were found to readily react with aryl, acyl, and arenesulfonyl isocyanates to give the corresponding acyl carbamoyl selenides 3 [RC(=O)SeC(=O)NHR′, R′ = aryl, C6H5CO, and 4-MeC6H4SO2] in good yields. Their tautomers [RC(=O)SeC(=NR′)OH] were also detected by 1H, 13C, and 77Se NMR spectroscopies. The structure of 3 [R = 2,6-(MeO)2C6H3, R′ = 4-MeC6H4] was characterized by X-ray crystallography, which showed that this molecule is stabilized by an intramolecular hydrogen bond between the carbonyl oxygen and the NH hydrogen to form a planar six-membered ring and by nonbonded interaction of the ortho methoxy oxygen with the carbonyl oxygen or the selenium atoms. 4-Methoxybenzoyl and 4-methoxythiobenzoyl N-(4-methylphenyl)carbamoyl sulfides (4 and 5) were shown by X-ray crystallography to similarly have a planar intramolecular six-membered ring formed by a hydrogen bond between the carbonyl oxygen or thiocarbonyl sulfur and NH hydrogen atoms. The tautomers [RC(=E)SC(=NR′)OH; E = O or S] of 4 and 5 also were detected spectroscopically. The reactions of 3h (R = 4-MeOC6H4, R′ = Ph) with sodium methoxide and p-toluidine gave sodium selenocarboxylate and the corresponding amides and urea as main products, respectively. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:250–258, 2001

Novel water-soluble diaryl tellurides, alkyl aryl tellurides, and dialkyl tellurides carrying sulfopropyl groups were prepared and found to possess potent peroxide decomposing and chain-breaking antioxidative capacity. The dilithium, disodium, dipotassium, and bis-tetramethylammonium salts of bis(4-hydroxyphenyl) telluride (4) were treated with 2.3 equiv of 1,3-propanesultone in aqueous tert-butyl alcohol to give the corresponding salts 5 of bis-O-sulfopropylated diaryl telluride. A variety of diaryl ditellurides were reduced with sodium borohydride in ethanol. Upon addition of propanesultone to the resulting sodium arenetellurolates, the corresponding 3-aryltellurenylpropanesulfonic acid sodium salts 8 were precipitated. Diphenyl diselenide and dibutyl ditelluride reacted similarly to afford the sodium salts of 3-benzeneselenenylpropanesulfonic acid (9) and 4-telluraoctanesulfonic acid (10), respectively. The glutathione peroxidase-like activity of the water-soluble compounds was assessed at pH = 7.4 by using the coupled GSSG reductase assay. Dialkyl telluride 10 turned out to be the most efficient catalyst. Several alkyl aryl tellurides 8 were also more efficient than any of the previously tested organotellurium compounds in this model. Bulky and electron-withdrawing aryl substituents seemed to reduce activity, whereas electron-donating groups enhanced it. Alkyl aryl selenide 9 was void of any catalytic activity. The novel compounds were also assessed by (1)H NMR spectroscopy for their capacity to catalyze the hydrogen peroxide oxidation of N-acetylcysteine in D(2)O under acidic conditions. In the presence of 0.01 mol % of the organotellurium catalyst, the thiol concentration was reduced to 50% within 12 min for the most active catalyst (compound 5b). Although many of the compounds showed high catalytic activity, it was not possible to rationalize their relative efficiency. The capacity of the novel organotellurium compounds to act as a scavengers of 1,1-diphenyl-2-picrylhydrazyl (DPPH) was also investigated. The organotelluriums seem to act primarily as electron donors in their reaction with DPPH. Compounds 8d, 10, and 8b were the most effective scavengers. Bulky or electron-withdrawing aryl substituents caused a reduction in activity, whereas electron-donating ones enhanced it. None of the compounds could match vitamin E in their scavanging capacity.

Dithiocarboxylic acids and their trimethylsilyl esters were found to readily react with potassium, rubidium, and cesium fluorides to give the corresponding alkali metal dithiocarboxylates 3-5 in moderate to good yields. A series of tetramethylammonium dithiocarboxylates 8 have been prepared in good yields by the reaction of sodium dithiocarboxylates 7 with tetramethylammonium chloride. The structures of potassium (3b), rubidium (4g), cesium (5f), and tetramethylammonium 4-methylbenzenecarbodithioates (8e) and tetramethylammonium 2-methoxybenzenecarbodithioate (8f) were characterized crystallographically. These heavier alkali metal salts (3b, 4g, 5f) have a dimeric structure [(RCSSM)(2), M = K, Rb, Cs] in which the two dithiocarboxylate groups are chelated to the metal cations which are located on the upper and lower sides of the plane involving the two opposing dithiocarboxylate groups. The K(+) cations interact with the tolyl fragment of a neighboring molecule, while the Rb(+) and Cs(+) cations interact with two neighboring tolyl fragments, in which the ipso and ortho carbons are positioned close to the metals. The interaction number of the metals with surrounding atoms is 8 for K(+) and Rb(+) and 12 for Cs(+). The C-S distances of the dithiocarboxylate group are different for the potassium salt 3b. In contrast, those of the rubidium salt 4g and cesium salt 5f are equal. Similarly, the chelating sulfur-metal bond distances of 3b are different, while those of 4g and 5f are almost equal. The dihedral angles of the phenyl ring and dithiocarboxylate plane increase in the order of the K, Rb, and Cs salts. The structural analysis of sodium 4-methylbenzenecarbodithioate (7g) revealed the presence of 4-CH(3)C(6)H(4)CS(2)Na(0.36). In contrast, the tetramethylammonium salts 8 are monomeric where the cation moieties are located out of the dithiocarboxylate plane. The potassium 3, rubidium 4, and cesium dithiocarboxylates 5 readily reacted with methyl iodide or triorganotin chlorides at room temperature to give the corresponding methyl 9 and triorganotin dithioesters 10 in good yields. At 0 degrees C, the reactivity of the rubidium 4 and cesium salts 5 to methyl iodides decreases dramatically compared with those of the sodium salts 7 and potassium salts 3.

The first synthesis and characterization of sodium and potassium tellurocarboxylates were achieved by the reaction of acyl chlorides with the corresponding alkali metal tellurides. The salts are yellow to red solids or oils. The aliphatic derivatives are very sensitive toward oxygen and very thermally sensitive. However, the aromatic derivatives are relatively stable and can be stored for 1 week below -5 degrees C and under oxygen-free conditions. The most practical method for the synthesis of Te-alkyl telluroesters was established by the reaction of the sodium and potassium tellurocarboxylates with alkyl iodides at 0 degrees C. The first X-ray structural analysis of telluroesters (RCOTeR') was carried out for Te-methyl 4-chlorobenzenecarbotelluroate (4-ClC(6)H(4)COTeCH(3)), whose crystals are monoclinic (P2(1)/a) with a = 5.975(3) A, b = 14.517(2) A, c = 10.617(3) A, beta = 92.74(3) degrees, V = 919.8(4) A(3), and Z = 4. The molecule was nearly planar. The C=O and C-Te bond lengths are 1.204(3) and 2.153(3) A, respectively, indicating C=O double and C-Te single bonds. The C-Te-C angle of the C(O)TeCH(3) moiety is close to a right angle (92.3 degrees ), much more narrow compared with those [C-E-C, E = O (>105 degrees ), S (>102 degrees ), Se (>95)] of common esters and thio- and selenoesters (ArC(O)ER', E = O, S, Se; R' = alkyl). The nu(C=O) bands and the (13)C=O and (125)Te NMR spectra of the sodium and potassium tellurocarboxylates are discussed in comparison with those of other alkali metal or oxygen, sulfur, and selenium isologues.

The reaction of selenothioic acid S -alkyl esters with electron deficient alkynes was carried out under reflux in toluene to give cyclic selenides in good yields. On the contrary, the similar reaction in MeOH or CH 2 Cl 2 with Et 3 N afforded acyclic divinyl selenides in good to high yields.

Acylselenenyl halides 2(X = Cl, Br) have been generated from RC(O)SeAsPh21 and N-halogenosuccinimide, and the chlorides 2(X = Cl) have been treated with enol silyl ethers to give Se-β-oxoalkyl Selenoesters 5 in good yields.

The reaction of bis(acyl) tellurides with primary or secondary amines or potassium ethanolate yielded the corresponding tellurocarboxylic acid salts, which are readily oxidized with iodine or benzenesulfonyl chloride to afford novel bis(acyl) ditellurides.