McMurry reaction

This reductive coupling can be viewed as involving two steps. First is the formation of a pinacolate (1,2-diolate) complex, a step which is equivalent to the pinacol coupling reaction. The second step is the deoxygenation of the pinacolate, which yields the alkene, this second step exploits the oxophilicity of titanium. Several mechanisms have been discussed for this reaction. Bogdanovic and Bolte identified the nature and mode of action of the active species in some classical McMurry systems, and an overview of proposed reaction mechanisms has been published. It is of note that titanium dioxide is not generally a product of the coupling reaction. Although it is true that titanium dioxide is usually the eventual fate of titanium used in these reactions, it is generally formed upon the aqueous workup of the reaction mixture. ==Background and scope==

The reaction was discovered independently by three different groups in 1973-74: Mukaiyama in Japan, Tyrlik in Poland, and McMurry in the USA. McMurry later described his discovery as being serendipitous. McMurry and Fleming coupled retinal to give carotene using a mixture of titanium trichloride and lithium aluminium hydride. : In another example, the Nicolaou's total synthesis of Taxol uses this reaction, although coupling stops with the formation of a cis-diol, rather than an olefin. Optimized procedures employ the dimethoxyethane complex of TiCl3 in combination with the Zn(Cu). The first porphyrin isomer, porphycene, was synthesised by McMurry coupling. : isomer, synthesis from bipyrrole dialdehyde through McMurry coupling reaction ==References==