Diisobutyl telluride

The previously described diisobutyl telluride/titanium(IV) system (see Section 4.1.1.3) also promotes similar Reformatsky-type reactions. In this case, however, the products are... 

Allyldiisobutyltelluronium bromide (0.87 g, 2.4 mmol) and KOt-Bu (0.269 g, 2.4 mmol) are placed in a reaction vessel under Nj, and dry THF (4 mL) is added with stirring at -78°C. After a few minutes, a solution of benzaldehyde (0.216 g, 2 mmol) in THF (2 mL) is added dropwise, and the reaction mixture is slowly allowed to warm to room temperature. Normal work-up followed by SiOj column chromatography gives diisobutyl telluride (0.55 g (95% based on the used salt) eluted by hexane) and 2-phenyl-3-vinyloxirane (0.356 g (82%) cisitrans = 85 15 eluted by 5% ether/hexane). 

Diisobutyl 2-Propen-l,l-ylideoe TeBurium4 0.87 g (2.4 mmol) of allyl diisobutyl telluronium bromide and 0.27 g (2.4 mmol) of potassium fert-butoxide are placed in a nitrogen-filled vessel. The vessel and 4 ml of dry tetrahydrofuran are cooled to — 78°. With stirring, the tetrahydrofuran is added dropwise to the mixture, stirring is continued for a few minutes, and then a solution of 0.216 g (2 mmol) of bcnzaldehydc in 2 ml of tetrahydrofuran is added dropwise to the ylide. The mixture is allowed to warm slowly to 20°. Work up and column chromatography on silica gel gives diisobutyl telluride and 2-phenyl-3-vinyIoxirane yield 82%. 

A useful and practical version of the above protocol involves a catalytic process in which the enone, a bromoallyl silane, cesium carbonate and diisobutyl telluride react in a one-pot procedure to give the desired cyclopropanes with a high c -stereoselectivity. 

With a catalytic amount of diisobutyl telluride method B. Chalcone (0.5 nunol), cesium carbonate (1.0 mmol), (ii)-3-bromo-l-trimethylsilylprop-l-ene (0.75 mmol), diisobutyl telluride (0.1 mmol), THF (5 cm ) and water (5 mm ) were mixed in a reaction tube and stirred at 50°C for a specific period of time. After 28 h, additional trimethylsilylallyl bromide (0.25 mmol) was added and stirring continued for 20 h. When the reaction was complete (monitored by TLC), work-up as for method A and flash chromatography of the residue on silica gel afforded the product, of purity >98% (GC). 

Heteroatom allylation. Diisobutyl telluride is a good leaving group therefore phenols, thiophenols, and anilines are readily allylated by this salt. 

Cyclopropanation. The derived ylide (1) is able to participate in cyclopropane ring formation with enones. It is not necessary to use the salt stoichiometically as diisobutyl telluride can be made catalytic. 

Coupling reaction of tosyl azide (11) with benzophenone (12) in a solution of diisobutyl telluride and titanium(IV) chloride in refluxing benzene (eq 4). 

Achiral tellurides were used in the catalytic epoxidation of aldehydes by Huang and coworkers in 1990. With diisobutyl telluride as a catalyst (20mol%), various aromatic, heteroaromatic, and non-primary aliphatic aldehydes can be epoxidized directly with aUyhc bromide to the corresponding vinyl epoxides in good yields with predominantly cis-selectivity [59], Later, they successfully extended this method to the cyclopropanation of a,(3-unsaturated ketones with aUyl bromides [60], The asymmetric version of the cyclopropanation was realized by Tang and coworkers in 2003 [61], using salt 43 directly as a catalyst (20mol%) in the reaction of chalcones with silylated aUyl bromide. The desired vinyl cyclopropanes were... 

In 1990, Huang et al. reported the synthesis of vinyl epoxides from aldehydes catalyzed by diisobutyl telluride (237). The ditelluride works with a variety of different aldehydes. An example is shown below (Schane 7.53) [198]. 

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