Tellurium-copper exchange

Table 5 Tellurium-copper exchange of vinylic tellurides with lithium cyanocuprates...

Recently, this unique characteristic of vinylic tellurides was explored in the enantioselective synthesis of macro-lactin A 205, an antiviral macrolactone extracted from sea bacteria. The first step of the synthesis featured the chiral epoxide 203 opening by the vinyl cyanocuprate 202, derived from a tellurium-copper exchange reaction using the vinylic telluride 201, obtained by hydrotelluration of 200 (Scheme 111). Further manipulation of 204 led to macrolactin A 205.271... 

Recently, the direct transformation of allyl- 206272 and aryl tellurides 209273 into the corresponding organocopper species 207 and 210 by tellurium-copper exchange was described. The resulting allyl 207 or aryl cuprates 210 were captured by coupling with vinyl triflates 208272 or by 1,4-addition to enones 211,273 respectively (Scheme 112). 

Solid 002(0211302)2 (natural uranium) was Irradiated with thermal neutrons for 10 min (flux not given) and the target was dissolved In concentrated hydrochloric acid. The solution was boiled for several minutes and was then made. 2-3 molar In the acid. A copper foil was introduced Into the solution and the fission product tellurium plated out on the foil. The coated foil was dissolved In 1 M nitric acid and passed through a cation exchange resin column (resin not designated) to remove the copper. The eluate was made basic with ammonia water. Iodide carrier added, and permitted to grow In for 70 m1n. The Iodide was oxidized to the free element and a number of I2 - I redox cycles were carried out. The Iodine was finally precipitated as the silver salt. 

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