Rieke copper

An important recent advance in the area is the demonstration that allyl chlorides readily form allylcopper species upon exposure to highly activated copper ( Rieke copper ). The resultant allylcoppers have been shown to react with a fairly wide range of nucleophiles (ketones, aldehydes, acid chlorides, enones, epoxides [after conversion to the cuprate], imines, and allyl bromides)56. Regiochemical considerations in such substitutions depend upon the cases studied, and are fairly complex. The allylcoppers formed have, in all cases, the least substituted C—Cu bond allyl transfer from these reagents is selective from the imposition of the allyl (enone electrophiles excepted)(equations 41 and 42). The allyl chloride... 

It has proven possible to add oxidatively highly activated copper metal ( Rieke copper ) to alkynyl bromides in moderate yields, to furnish acetylenic copper compounds (equation 44)10. Bubbling oxygen through the system resulted in the formation of homocoupling products. 

Aryl halides are excellent substrates for metal-halogen exchange by highly activated Rieke copper, affording aryl coppers at or below room temperature in fair to excellent yields. Functional groups such as nitriles, ketones and fluoride substituents are tolerated,... 

Table 5 Formation and Acylation of Stoichiometric Organocuprate Reagents prepared from Rieke Copper...

Moreover, the copper metal obtained by reduction of CuCl, CuI(PEt3) or Cu(SMe2)Cl with the lithium naphthalide, known as Rieke copper, is able to couple a range of aryl halides to biaryls at room temperature in very high yields [27]. For example, simple halobenzenes react with Rieke copper at room temperature to form phenylcopper(I) reagents which, upon refluxing in DME at 80 °C for 24 h, gave 66% of biphenyl. The... 

For the highly reaetive eopper metal forms, e.g. Rieke copper, oxidative addition to aryl halide occurs readily at room temperature or below [27]. At these temperatures oxidative addition of the resultant arylcopper(l) compound to the second molecule of aryl halide, or decomposition to biaryl proceeds very slowly or not at all. The arylcopper(l) compounds can then be homo-coupled or react with the aryl halides to form biaryl as the temperature is raised. In the classical Ullmann reaction employing... 

Finely divided, highly reactive, Rieke metal powders are normally prepared by reducing metal halides with potassium metal in refluxing tetra-hydrofuran. This clearly represents a laboratory safety hazard but sonication can produce these same powders under much milder conditions using the less reactive lithium metal at ambient temperatures [12]. Thus the preparation of Rieke copper, which normally requires an 8 h reflux with potassium in THF, can be achieved in less than 40 min at room temperature with sonication (Scheme 10.3). 

Chemical Modification of Halogenated Polystyrenes Using Rieke Calcium or Rieke Copper... 

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