Science of Synthesis

Heaney, H.; Christie, S., Science of Synthesis, (2004) 3, 590.

The need for inexpensive groups that can be utilized as retained ligands in mixed cuprate systems has already been highlighted in the introduction. One of the common, and most useful, approaches has been the use of thiophene derivatives. In any system where the ligand essentially acts as a sacrificial moiety there is a need for it to be inexpensive. With respect to the current problem, the ligand would have to be easily metalated, probably with lithium via reaction with butyllithium, so that reaction with copper(I) cyanide could produce the precursor cuprate. Thiophene lends itself well to these two criteria since it is inexpensive and is metalated essentially quantitatively in the 2-position. In addition, on reaction of 2-thienyllithium with copper(I) cyanide, a stable brown solution of the cyanocuprate (2-thienyl)CuCNLi is formed. The stability of this particular intermediate is best illustrated when one realizes that it is now a commercial product. However, it is also easily synthesized and the procedure is given below. The thienyl cyanocopper complex can be reacted further with another lithium or Grignard reagent to produce the desired mixed cuprate, (R1)(2-thienyl)CuLi•LiCN. Initial studies of this type of cuprate on reaction with epoxides showed that very efficient levels of control could be achieved, with essentially none of the thiophene transfer product being detected in the product distribution.[‌1540‌]

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References