One-Electron Reductions of Carbonyl Compounds and Esters Reductive Coupling

2 One-Electron Reductions of Carbonyl Compounds and Esters Reductive Coupling 

TiCil . treated with Cu/Zn couple (both in considarable excess) 

1) With the instant McMurry reaction time can be saved. This is important, particularly since the pre-reduction doesn t take place as once believed  

2) With a cheaper variant—which we will simply call low-budget McMurry reaction— insensitive and inexpensive titanium powder is used as a titanium source. This avoids the use of the moisture-sensitive and expensive DME-complexed TiCl3 whose oxidation level is much too high anyway. Titanium powder needs to be slightly etched superficially with trimethylchlorosilane (which is also inexpensive)  

3) With the catalytic McMurry reaction a few mole percent of DME-free TiCl3 are sufficient to run the reaction to completion. The trick is that stoichiometrically added zinc continuously provides low-valent titanium and the oxygen that is released is bound by a supersto-ichiometric amount of chlorosilane as a disilyl ether ( disiloxane ). This procedure has been utilized for many indole syntheses based on the McMurry reaction (Side Note 17.6). 

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