Salts telluronium

A treatment of 2-butyltelluroaniline with an equimolar amount of bromoacetic acid results in spontaneous cyclization of the formed telluronium salt 31 to give 1-butylbenzotellurazinonium bromide 30. That the alkylation occurs at the tellurium and not at the nitrogen atom of 2-butyltelluroaniline has been proved by the isolation of the methyl ester of 31 in 60% yield when the amine was coupled with methyl bromoacetate under the same reaction conditions. Elimination of butyl bromide from 30 readily occurs on heating of its DMF solution leading to 2//-l,4-benzotellurazin-3(4//)-one 32 in 90% yield. 

It is well known that aziridination with allylic ylides is difficult, due to the low reactivity of imines - relative to carbonyl compounds - towards ylide attack, although imines do react with highly reactive sulfur ylides such as Me2S+-CH2-. Dai and coworkers found aziridination with allylic ylides to be possible when the activated imines 22 were treated with allylic sulfonium salts 23 under phase-transfer conditions (Scheme 2.8) [15]. Although the stereoselectivities of the reaction were low, this was the first example of efficient preparation of vinylaziridines by an ylide route. Similar results were obtained with use of arsonium or telluronium salts [16]. The stereoselectivity of aziridination was improved by use of imines activated by a phosphinoyl group [17]. The same group also reported a catalytic sulfonium ylide-mediated aziridination to produce (2-phenylvinyl)aziridines, by treatment of arylsulfonylimines with cinnamyl bromide in the presence of solid K2C03 and catalytic dimethyl sulfide in MeCN [18]. Recently, the synthesis of 3-alkyl-2-vinyl-aziridines by extension of Dai s work was reported [19]. 

Cation-Anion Interactions Involving Selenonium and Telluronium Salts... 

Dibutyltelluronium benzylide, generated by treatment of the telluronium salt with potassium f-butoxide, behaves similarly to the above-stabihzed ylides, undergoing Wittig-type olefmations with aromatic aldehydes. 

Method C - using telluronium salts (typical procedure). A mixture of car-bethoxymethyldibutyltelluronium bromide (0.99 g, 2.5 mmol) and 4-nitrobenzaldehyde (0.38 g, 2.5 mmol) is refluxed in THF (30 mL). After 6 h, it is quenched with HjO and extracted with ether. The organic extract is purified by recrystallization to afford pure ( )-methyl 3-(4 -nitrophenyl)propenoate (0.491 g (95%)). 

Intensive investigations have been devoted to the synthesis of vinyl cyclopropanes by using allylic telluronium salts. Vinyl cyclopropanes are important compounds as versatile synthetic intermediates and as participants in the structure of several biologically active natural compounds. ... 

Thus, allyl telluronium ylides generated in situ from the corresponding telluronium salts in the presence of Li salts react with a,)3-unsaturated esters and amides to afford trans-2-vinyl-/rany-3-substituted cyclopropyl compounds in high yieds. 

General procedure - with telluronium salt method A mixture of trimethylsilylprop-2-enyl(di-isobutyl)telluronium bromide (0.33 g, 0.75 mmol), cesium carbonate (0.25 g, 0.75 mmol), chalcone (0.5 mmol), and DME (5 mL) and water (5 mm ) was heated at 70°C for specific periods of time. When the reaction was complete (monitored by TLC), the resulting mixture was eluted with ethyl acetate through a short column of silica gel. Removal of the solvent and flash chromatography on silica gel gave the desired pure product, of purity >98% (GC). 

General procedure Condition A A solution of base (0.75 mmol) in THF (0.75 mL) was added dropwise to a solution of telluronium salt (0.75 mmol) + LiBr (0.75 mmol) in 6.5 mL of solvent at -78°C under N2. The mixture was stirred for 5 min, and then the a, -unsaturated compound (0.5 mmol) in solvent (1 mL) was added. The reaction mixture was allowed to warm to room temperature after the reaction was completed. Usual workup and flash chromatography gave the pure product. Condition B Similar to condition A, only there was no lithium salt addition. 

The reaction of aUyl telluronium salts with phenols in the presence of solid NaOH in THF leads to allylic ethers in excellent yields. ... 

Correlate reaction the reaction of telluronium salts with carbonyl compounds mediated by organoUthium reagents - formation of secondary alcohols... 

With the telluronium salts (a2), (b), (c) and (d), phenyl, benzyl, cyanomethyl and (trimethylsilyOpropargyl groups, respectively, are transferred in preference to the other groups. 

The )3-hydroxynitriles obtained from telluronium salt (c) form an important class of compounds since the cyano group can be submitted to several transformations. ... 

The importance of the propargyhc anions in synthetic chemistry enhances the utility of the reaction involving telluronium salt (d). 

Reaction of telluronium salts/n-BuLi with carbonyl compounds synthesis of alcohols with telluronium salt (a2) (typical procedure) A solution of n-BuLi (1.1 mmol) in hexane is added to a solution of the telluronium salt (0.459 g, 1.2 mmol) in THF (6 mL) at -78°C under N2. The mixture is warmed at -60°C and stirred for 10 min. After cooling again at -78°C, p-chlorobenzaldehyde (0.140 g, 1.0 mmol) in THF (2 mL) is added. The mixture is then allowed to warm at room temperature. After the reaction is complete (monitored by TLC), the usual work-up and flash chromatography yield pure p-chlorophenyl(phenyl)carbinol. 

The semi-stabilized telluronium ylides, generated in situ from the corresponding telluronium salts (156 R1 = CH=CHSiMe3, CH=CH2, CH=CHMe, CH=CHPh, Ph), have been reported to react with a,/(-unsaturated carbonyl compounds (157 R2 = Ph, OR, NR)) to afford 2-vmylcyclopropyl derivatives (158) with high... 

The telluronium salt 142 obtained from telluroisochromane and o -bromo-4-chloroacetophenone upon treatment with silver o-bromcamphor-sulfonate produced two diastereomers which were separated by crystallization from ethanol and then converted to their enantiomeric picrates. Racemization due to inversion of their pyramidal configuration at the tricoordinate tellurium center occurs slowly and was accomplished at room temperature over 20 days (45JCS37). 

By contrast with the structurally congeneric telluronium salts R3Te + X that readily eliminate alkyl or aryl halides RX upon heating either in the solid or in pyridine solution (74MI1 83MI2), benzoxatelluroles 29 exhibit enhanced thermal stability and do not eliminate butyl halides even under prolonged heating. 

Telluronium salts like 110 are themselves very strong alkylating agents, which is illustrated by the equilibrium observed in DMSO-[Pg.101]

Triorganyl-sulfonium, -selenonium and -telluronium salts are reduced by carbon dioxide radical anions/solvated electrons produced in aqueous solution by radiolysis. The radical expulsion accompanying reduction occurred with the expected leaving group propensities, i.e. benzyl > secondary alkyl > primary alkyl > methyl > phenyl. Much higher product yields in the reduction of selenonium and telluronium compounds have been accounted for in terms of a chain reaction with carbon-centred radicals, with formate serving as the chain transfer agent.282... 

Scheme 10.24 Catalytic asymmetric cyclopropanation using telluronium salts.

To a mixture of a,/ -unsaturated compound (0.25 mmol), CS2CO3 (0.27 mmol), and telluronium salt catalyst (0.05 mmol) in THF (0.5 mL) was added trimethyl-silyl allylic bromide (0.5 mmol) in portions over 8 h at reflux. When the reaction was complete (monitored by GC), the resulting mixture was filtered through short silica gel column and washed with ethyl acetate. The filtrate was concentrated, and the residue was purified by FC to afford the desired product. 

Telluronium ylides,118 derived from triorganotelluronium salts 63, react with aldehydes, ketones, and a,/3-unsaturated esters to give different products depending on the nature of the substituent at the a-carbon of the telluronium salt 63. In Scheme 31,121-123 examples of such transformations are given. 

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