Hydroxy tellurides

The 7-hydroxy telluride 161 is prepared by hydrotelluration of methyl vinyl ketone, followed by in situ reduction with sodium borohydride.154 Treatment of 161 with 2 equiv. of nBuLi, followed by capture of the dianion 162 with electrophiles, gives the corresponding alcohols 163.252 Dianions like 162 can be transmetallated with CeCf , leading to organometallics of the type 164, which on reaction with lactones give spiroketals (Scheme 94).253... 

Methyl (3-hydroxy)propyl telluride (typical procedure) MeTeLi. A suspension of Te powder (12.8 g, 0.1 mol) in THE (100 mL) is frozen in a liquid N2 bath, and then MeLi (66.7 mL of a 1.5 M solution in ether, 0.1 mol) is injected into the flask. The mixture is allowed to thaw and is stirred magnetically for a further 30 min at room temperature. The resulting yellow-orange solution is stored under N2 and used within 2 h. 

Aryltellnrinyl acetates, generated as previously described from the corresponding tellurinic anhydrides and acetic acid, add to hydroxy olefins, giving tellurinylated cyclic ethers. The reaction is performed in refluxing acetic acid or in chloroform in the presence of BFj EtjO. Owing to their hygroscopicity and intractable nature, the products are reduced with hydrazine hydrate, and isolated as tellurides (as for the aminotellurinylation reactions). 

It was discovered that the acetyl derivalive of iV-hydroxy-2-thiopyridone is especially suitable as a source of methyl radicals, being photolysed by irradiation with a simple tungsten lamp. On this basis, and because of the high radicophilicity of tellurides (especially anisyl tellurides), a radical exchange occurs when the reagent is irradiated in the presence of an... 

Selenides and tellurides can be prepared similarly.774 When epoxides are substrates, p-hydroxy sulfides are obtained in a manner analogous to that mentioned in 0-35. Epoxides can also be directly converted to episulfides,775 by treatment with a phosphine sulfide such as PI13PS776 or with thiourea and titanium tetraisopropoxide.777... 

Tellurophene2 Sodium hydrogen telluride is prepared from 12.7 g (0.1 mol) tellurium and sodium in 150 ml dimethylformamide and the resulting solution cooled to 0°. A solution of 8.4 g (0.08 mol) of l-chloro-2-hydroxy-3-butyne in 20 ml ethanol is added dropwise during 30 min. The mixture is kept at 20° for 1 h and then treated with 5.6 g (0.1 mol) of powdered potassium hydroxide. The mixture is heated for 2 h at 100°, then cooled, treated with water, and extracted with diethyl ether. The extract is washed with water, dried, and concentrated. The residue is dissolved in a mixture of acetic acid/ethanol (1 8) (100 ml per 15 g) and the solution refluxed for 2 h. The mixture is then treated with water and extracted with diethyl ether. The extract is dried, filtered, and concentrated. The residue is distilled yield 10% b.p. 97/100 torr. 

REDUCTION, REAGENTS Bis(N-methylpi-perazinyl)aluminum hydride. Borane-Di-methyl sulfide. Borane-Tetrahydrofurane. Borane-Pyridine. n-Butyllithium-Diisobu-tylaluminum hydride. Calcium-Amines. Diisobutylaluminum hydride. 8-Hydroxy-quinolinedihydroboronite. Lithium aluminum hydride. Lithium 9-boratabicy-clo[3.3.1]nonane. Lithium n-butyldiisopro-pylaluminum hydride. Lithium tri-j c-butylborohydride. Lithium triethylborohy-dride. Monochloroalane. Nickel boride. 2-Phenylbenzothiazoline. Potassium 9-(2,3-dimethyl-2-butoxy)-9-boratabicy-clo[3.3.1]nonane. Raney nickel. Sodium bis(2-methoxyethoxy)aluminum hydride. Sodium borohydride. Sodium borohy-dride-Nickel chloride. Sodium borohy-dride-Praeseodymium chloride. So-dium(dimethylamino)borohydride. Sodium hydrogen telluride. Thexyl chloroborane-Dimethyl sulfide. Tri-n-butylphosphine-Diphenyl disulfide. Tri-n-butyltin hydride. Zinc-l,2-Dibromoethane. Zinc borohydride. 

Tellurophenes were obtained by intramolecular dehydration of 3-hydroxy-2,3-dihydro-tellurophenes that were prepared from sodium hydrogen telluride and l-chloro-2-hydroxy-3-butynes. ... 

Both the C and N chemical shifts of a number of quinoxalines substituted at position 2 with the n-electron excess 2 -benzo[ ]furanyl substituent, which has at position 3 a hydroxy or amino group, could be satisfactorily calculated by the GIAO method on the basis of HF and DFT ab initio structures. Quantum mechanical calculations using the 3-21 G(d) basis-set were performed on some p-substituted diaryl tellurides and aryl Me tellurides, and the corresponding cationic radicals of these compounds. Calculated relative radical stabilization energies were shown to correlate with experimental data, and the peak oxidation potentials and Te chemical shifts were... 

The synthesis of l(7)-menthene-2,8-diols (655) has been mentioned (Vol. 4, p. 526, Ref. 503) the two isomers have now been isolated from Osmitopsis asteriscoidesThe known acetate 656, an insect repellent, has been isolated from Mentha haplocalyx oil, and a review of synthetic methods has been published by Verghese. In this connection, attention is drawn to a method for reducing an epoxide in the presence of a ketone, by reaction with phenyl telluride anion, PhTe, then triphenyltin hydride. The dihydrocarvone epoxides (657) yielded the hydroxy dihydroketone 658 corresponding to 656. Note also... 

C-Glycopyranosides may be obtained from glycopyranosyl halides via intermolecular addition of glycopyranosyl radicals [129]. In a more useful example, the a-aminoacrylate 192 was used as the radical acceptor for preparation of C-glycosyl amino acids 193 and 194 [130] (Scheme 66). In a concise synthesis of showdomycin (197), Barton utilized the trigger reaction of the 7V-hydroxy-2-thiopyridone derivative and the exceptional radicophilicity of tellurides in concocting the conditions for the conversion from the anisyl telluride 195 to the intermediate 196 after oxidative elimination [131] (Scheme 67). In Keck s synthesis of (-t-)-pseudomonic acid C (201), the intermediate 200 was prepared via stereocontrolled intermolecular addition of the radical generated from the iodide 198 to the allylic sulfone 199 [132] (Scheme 68). 

When BuLi was added to aryltellurol esters in THF/Et20 at low temperatures in the presence of pinacolone as an electrophile, a-hydroxy ketones 90 were obtained in high yields via aroyllithiun 89 together with dibutyl telluride (Eq.66) [124]. 

Photonucleophilic aromatic substitution reactions of phenyl selenide and telluride with haloarenes have also been proven to involve the S jlAr mechanism, with the formation of anion radical intermediates. Another photonucleophihc substitution, cyanomethylation, proves the presence of radical cations in the reaction mechanism. Liu and Weiss have reported that hydroxy and cyano substitution competes with photo substitution of fluorinated anisoles in aqueous solutions, where cation and anion radical intermediates have been shown to be the key factors for the nucleophilic substitution type. Rossi et al. have proposed the S j lAr mechanism for photonucleophihc substitution of carbanions and naphthox-ides to halo anisoles and l-iodonaphthalene. > An anion radical intermediate photonucleophilic substitution mechanism has been shown for the reactions of triphenyl(methyl)stannyl anion with halo arenes in liquid ammonia. Trimethylstannyl anion has been found to be more reactive than triphenylstannyl anion in the photostimulated electron- transfer initiation step. 

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