Search

Coumarins, 4-hydroxycoumarins, and 4-hydroxyquinolin-2(1H)-ones can be conveniently prepared by treatment of alpha-halocarboxylic acid esters of salicylaldehyde, o-hydroxyacetophenone, methyl salicylate, and methyl N-methyl- or N-phenylanthranilates with sodium or lithium telluride. Phenylketene formation competes with cyclization of the alpha-chlorophenylacetate ester of methyl salicylate as demonstrated by a trapping experiment with benzylamine. Elemental tellurium may be recovered and reused.

[reaction: see text] Acylcyclopropanemethanol tosylates undergo rapid ring opening at room temperature by the action of lithium telluride to produce the enolate of a homoallylic ketone. The enolate can be protonated to yield the corresponding ketone or treated with benzaldehyde to give the aldol product with good syn or anti diastereoselectivity depending on the conditions.

Telluride ion reacts with an oxiranemethanol toluenesulfonate in toluene under phase-transfer conditions to give an allylic alkoxide anion that is trapped by addition to an adjacent α,β-unsaturated ester to yield a furan derivative. Use of a non-racemic oxiranemethanol tosylate gives two furan diastereomers in a ratio of 56:44.

Non-racemic or racemic allylic amines are obtained by treatment of sulfonate esters of 5-hydroxymethyl-2-oxazolidinones with telluride ion.

Sulfonate esters of aziridinemethanols are converted to allylic amines by treatment with telluride ion obtained by reduction of elemental tellurium. In the course of the reaction, tellurium(0) is reformed and may be reused, thus removing the need to dispose of a key reagent. The telluride reaction yields optically active allylic amines from optically active aziridinemethanols. In contrast to many ring-openings of aziridines by nucleophiles, activation by an electron-withdrawing substituent on nitrogen is not necessary and is even detrimental.

Elemental tellurium can be reduced by rongalite (HOCH2SO2Na·2H2O)-KOH in the solid phase by application of ultrasound or by microwave irradiation. Without solvent, the organic substrate (eg sulfonate ester of an oxiranemethanol) is added with further sonication or irradiation to yield the desired organic product (eg allylic alcohols) and elemental Te which may be recycled. Phase-transfer conditions (water-toluene) also are satisfactory.

Treatment of 1,2-diol cyclic sulfates (1,3,2-dioxathiolane 2,2-dioxides) with telluride ion, generated in situ by reduction of the element, yields alkenes rapidly (10 min- 2 h) under mild conditions (0 °C to room temperature). The reaction is stereospecific, e.g. meso-2,3-diphenylethane 2,3-diol → cis-stilbene; d,l-2,3-diphenylethane-2,3-diol → trans-stilbene. Unsaturated mannose and ribose derivatives have been obtained, and diethyl (-)-tartrate gives diethyl fumarate. The reaction may be performed with 0.1 equiv or less of elemental tellurium in the presence of a stoichiometric amount of reducing agent. Reaction of telluride ion with cyclic thionocarbonates (1,3-dioxolane-2-thiones) of meso- and d,l-1,2-diphenylethane-1,2-diol yields cis- and trans-stilbene, respectively.

Treatment of p-toluenesulfonates of epoxides of specific primary allylic alcohols with telluride ion, prepared in situ by reduction of relatively nontoxic elemental tellurium, installs the two key secondary alcohol functions that occur in the lactone part of the cholesterol-lowering drugs, compactin, mevinolin, and lovastatin. Since the epoxides of the primary allylic alcohol starting materials can be synthesized in optically active form by the Sharpless-Katsuki asymmetric epoxidation (SAE) process, the stereospecific telluride transposition can give optically active secondary allylic alcohols configured for maximum inhibition of cholesterol formation

As little as 0.1 molar equivalent of elemental tellurium in combination with excess (up to 3 molar equivalents) reducing agent (HOCH 2 SO 2 Na·2H 2 O, NaBH 4 , or LiEt 3 BH) effects the telluride-ion mediated transposition of allylic hydroxyl groups and carbon-carbon double bonds that proceeds via the epoxy tosylate. The workup is much more convenient than when a molar equivalent of tellurium is used.

Treatment of glycidyl acetates with telluride ion (Te 2- ) produced by reduction of elemental Te with LiEt 3 BH yields allylic alcohols by loss of the epoxide oxygen atom and the acetyl group from the ester. If the glycidyl acetate is disubstituted at C-3, a rearrangement to an isomeric allylic alcohol competes with the deoxygenation-deacetylation. Triethylborane, a byproduct in the reduction of Te, is believed to play an important role as a Lewis acid since when it is absent or removed by addition of fluoride ion the reaction is extremely slow

Good yields of enantiomeric allylic alcohols can be obtained in high enantiomeric excess (ee) by combining the Sharpless-Katsuli asymmetric epoxidation process (SAE) with tellurium chemistry. The advantages of the tellurium process are as follows: (1) the 50% yield limitation on the allylic alcohol in the Sharpless linetic resolution (SKR) can be overcome; (2) allylic tertiary alcohols which are unsatisfactory substrates in the SKR can be obtained in high optical purity; (3) optically active secondary allylic alcohols with tertiary allyl substituents (e.g. tert-butyl) at C-1 can be obtained in high ee; (4) optically active sterically congested cis secondary alcohols can be obtained in high ee; and (5) the nuisance of the slow SAE of some vinyl carbinols can be avoided

Sharpless epoxidation, aminohydroxylation, and aziridination procedures provide substrates for the tellurium-triggered synthesis of racemic and non-racemic allylic amines under phase-transfer conditions.

We report that a new catalyst, palladium (II) acetate-tert-alkyl isocyanide, permitted the intermolecular bis-silylation of alkynes by otherwise unreactive disilanes, such as hexamethyldisilane and 1,2-diphenyl-1,1,2,2-tetramethyldisilane, to give bissilylated alkenes in yields up to 98%. Extension of the reaction of the intramolecular bis-silylation of carbon-carbon triple bonds led to the regioselective formation of cyclic organosilicon compounds in good yield

Treatment of p-toluenesulfonates of epoxides of specific primary allylic alcohols with telluride ion, prepared in situ by reduction of relatively nontoxic elemental tellurium, installs the two key secondary alcohol functions that occur in the lactone part of the cholesterol-lowering drugs, compactin, mevinolin, and lovastatin. Since the epoxides of the primary allylic alcohol starting materials can be synthesized in optically active form by the Sharpless-Katsuki asymmetric epoxidation (SAE) process, the stereospecific telluride transposition can give optically active secondary allylic alcohols configured for maximum inhibition of cholesterol formation

Treatment of 1,2-diol cyclic sulfates (1,3,2-dioxathiolane 2,2-dioxides) with telluride ion, generated in situ by reduction of the element, yields alkenes rapidly (10 min- 2 h) under mild conditions (0 °C to room temperature). The reaction is stereospecific, e.g. meso-2,3-diphenylethane 2,3-diol → cis-stilbene; d,l-2,3-diphenylethane-2,3-diol → trans-stilbene. Unsaturated mannose and ribose derivatives have been obtained, and diethyl (-)-tartrate gives diethyl fumarate. The reaction may be performed with 0.1 equiv or less of elemental tellurium in the presence of a stoichiometric amount of reducing agent. Reaction of telluride ion with cyclic thionocarbonates (1,3-dioxolane-2-thiones) of meso- and d,l-1,2-diphenylethane-1,2-diol yields cis- and trans-stilbene, respectively.

Elemental tellurium can be reduced by rongalite (HOCH2SO2Na·2H2O)-KOH in the solid phase by application of ultrasound or by microwave irradiation. Without solvent, the organic substrate (eg sulfonate ester of an oxiranemethanol) is added with further sonication or irradiation to yield the desired organic product (eg allylic alcohols) and elemental Te which may be recycled. Phase-transfer conditions (water-toluene) also are satisfactory.

Non-racemic or racemic allylic amines are obtained by treatment of sulfonate esters of 5-hydroxymethyl-2-oxazolidinones with telluride ion.

Sharpless epoxidation, aminohydroxylation, and aziridination procedures provide substrates for the tellurium-triggered synthesis of racemic and non-racemic allylic amines under phase-transfer conditions.

[2471-91-2]xk C8H8O2S (MW 168.21) InChI = 1S/C8H8O2S/c9-11(10)5-7-3-1-2-4-8(7)6-11/h1-4H,5-6H2 InChIKey = RBXWSNGDUIKIQJ-UHFFFAOYSA-N (a source of o-quinodimethanes1 that are useful diene intermediates in Diels–Alder reactions; a source of benzocyclobutene) Physical Data: mp 150–151 °C. Solubility: sol EtOH, CHCl3, C6H6, boiling water; slightly sol Et2O. Preparative Methods: by oxidation of 1,3-dihydrobenzo[c]thiophene;2 from α,α′-Dibromo-o-xylene, rongalite (Sodium Hydroxymethanesulfinate, HOCH2SO2Na·2H2O), and Sulfur Dioxide.3 Purification: recrystallization (H2O; H2O–EtOH; CH2Cl2–petroleum ether; CHCl3–C6H6; C6H6–petroleum ether). Handling, Storage, and Precautions: unstable to alkali and concentrated H2SO4.

Racemic trans -secondary allylic alcohols can be converted to homochiral cis -secondary allylic alcohols by means of a telluride-mediated transposition reaction applied to the homochiral glycidol obtained from a Sharpless kinetic resolution. (+)-Linalool is obtained in >95% enantiomeric excess from geraniol, an example of a transposition of a primary allylic alcohol to a homochiral tertiary alcohol.

Coumarins, 4-hydroxycoumarins, and 4-hydroxyquinolin-2(1H)-ones can be conveniently prepared by treatment of alpha-halocarboxylic acid esters of salicylaldehyde, o-hydroxyacetophenone, methyl salicylate, and methyl N-methyl- or N-phenylanthranilates with sodium or lithium telluride. Phenylketene formation competes with cyclization of the alpha-chlorophenylacetate ester of methyl salicylate as demonstrated by a trapping experiment with benzylamine. Elemental tellurium may be recovered and reused.

[reaction: see text] Acylcyclopropanemethanol tosylates undergo rapid ring opening at room temperature by the action of lithium telluride to produce the enolate of a homoallylic ketone. The enolate can be protonated to yield the corresponding ketone or treated with benzaldehyde to give the aldol product with good syn or anti diastereoselectivity depending on the conditions.

Thiete 1,1-dioxide and 3-chlorothiete 1,1-dioxide intermediate: Thietane 1,1-dioxide (14.0 g, 0.132 mol) intermediate: 3-chlorothietane 1,1-dioxide (8.0 g, 0.057 mol) intermediate: 3,3-dichlorothietane 1,1-dioxide (4.0 g, 0.023 mol) product: thiete 1,1-dioxide product: 3-Chlorothiete 1,1-dioxide Keywords: elimination, dehydrohalogenation; elimination, dehydrohalogenation; halogenation, chlorination; halogenation, chlorination; oxidation, S SO2; photochemical reactions; photochemical reactions; toluene

(anhyd) [16721-80-5] HNaS (MW 56.07) InChI = 1S/Na.H2S/h;1H2/q+1;/p-1 InChIKey = HYHCSLBZRBJJCH-UHFFFAOYSA-M (hydrate) [140650-84-6] (a nucleophile and reducing agent derived from H2S; a reagent for the synthesis of thiols1 and other divalent sulfur compounds,2 including thiocarbonyl derivatives;3 reduces aromatic nitro groups to amines4) Physical Data: mp (hydrate) 52–54 °C; anhyd, 350 °C; d 1.79 g cm−3; pKa (HS− ⇌ S2− + H+) 14.15. Solubility: v sol H2O; sol EtOH, DMF (colored solution). Form Supplied in: yellow chips (NaSH·xH2O, may be principally NaSH·2H2O); also available anhydrous; may contain Na2S, Na2S2O3 Na2CO3. Analysis of Reagent Purity: iodometric titration.5 Preparative Methods: saturation of ethanolic Sodium Hydroxide with Hydrogen Sulfide;5 anhydrous NaSH is obtained by precipitation with ether. Saturation with H2S shifts the equilibrium, 2NaSH ⇌ Na2S + H2S, to the left, as does operation in a solvent less polar than water or addition of NaHCO3 to Na2S. Handling, Storage, and Precautions: store in cool, dry place under nitrogen. Exposure to air forms Na2S2O4 and Na2CO3; very hygroscopic. Flammable; produces SO2 on combustion. Stench. A reducing agent. Incompatible with acids (produces H2S), with strong oxidizing agents, and with Zn, Al, and Cu. Corrosive (NaSH + H2O ⇌ NaOH + H2S). Use in a well-ventilated fume hood. Toxicity like that of Na2S. Extremely destructive to mucous membranes, eyes, upper respiratory tract, and skin. Can cause blindness; inhalation can be fatal. Decontamination with FeCl3 (production of insoluble iron sulfides).

[91-13-4] C8H8Br2 (MW 263.97) InChI = 1S/C8H8Br2/c9-5-7-3-1-2-4-8(7)6-10/h1-4H,5-6H2 InChIKey = KGKAYWMGPDWLQZ-UHFFFAOYSA-N (a source of o-quinodimethane, a highly reactive diene useful in Diels–Alder reactions;1 an electrophile for the synthesis of carbo- and heterocyclic compounds including macrocycles (cyclophanes, crown ethers, hemispherands, spherands),2 cryptands,3 hemicarcerands,4 vaulted cappedophanes,5 bicyclic compounds,6 spirocyclic compounds;7 a protective group reagent for diols8) Alternate Name: 1,2-bis(bromomethyl)benzene. Physical Data: mp 95 °C (CHCl3–EtOH); bp 140 °C/20 mmHg; d 1.960 g cm−3; dipole moment (hexane, 20 °C) 1.98 D. Solubility: sol ethanol, ether, chloroform; slightly sol petroleum ether. Form Supplied in: commercially available as a solid. Purification: recrystallization from 95% ethanol (3 mL g−1), petroleum ether (bp 60–80 °C) (19 mL g−1), chloroform (1 mL g−1). Column chromatography (silica gel, cyclohexane–ethyl acetate). Handling, Storage, and Precautions: avoid moisture; corrosive (forms HBr on hydrolysis); lachrymator; not mutagenic in Ames test; decontaminate by soaking apparatus, etc. in alcoholic alkali for 24 h or longer.

[1310-61-8] HKS (MW 72.18) InChI = 1S/K.H2S/h;1H2/q+1;/p-1 InChIKey = ZOCLAPYLSUCOGI-UHFFFAOYSA-M (a nucleophile and reducing agent similar to NaSH; useful in the synthesis of thiols,1 thioethers,2 and thiocarbonyl compounds3) Physical Data: mp 455 °C; d 1.68–1.70 g cm−3. Solubility: very sol H2O; sol EtOH. Form Supplied in: commercially available as a crystalline solid; colorless when pure. May be contaminated with K2S2O3 and K2CO3. Preparative Method: saturation of ethanolic KOH by H2S.4 Handling, Storage, and Precautions: extremely hygroscopic. Darkens on heating to yellow, then deep red at mp. Aqueous solutions evolve H2S on heating (KSH + H2O  KOH + H2S), and decompose in air to polysulfides and H2S. Oxygen also yields K2S2O3 and traces of K2SO3. Carbon dioxide yields H2S and K2CO3. For other precautions and toxicity see Sodium Hydrogen Sulfide.

Treatment of methanesulfonate esters of terminal glycidols obtained by epoxidation in the Sharpless kinetic resolution (SKR) of 1-substituted 2-propenols (secondary allyl alcohols) with telluride ion (Te 2− ) converts the glycidols to allyl alcohols of the same stereochemical configuration as the unreacted enantiomer from the SKR

We report that a new catalyst, palladium (II) acetate-tert-alkyl isocyanide, permitted the intermolecular bis-silylation of alkynes by otherwise unreactive disilanes, such as hexamethyldisilane and 1,2-diphenyl-1,1,2,2-tetramethyldisilane, to give bissilylated alkenes in yields up to 98%. Extension of the reaction of the intramolecular bis-silylation of carbon-carbon triple bonds led to the regioselective formation of cyclic organosilicon compounds in good yield