Characterization of the Pinacolate Intermediates

With the TiQ3-Zn(Cu) system, each of the two reaction steps requires a one-electron reduction of Ti(III) by Zn [267]. TiCl2 [213] was also found to act as a one-electron reductant for the formation of the alkene from the pinacolate intermediate. Interestingly, deuterolysis experiments performed at an early stage of each of these reactions produced 1-phenylethanol with 98% deuterium incorporation at the 1-position. This result indicates that the precursor of the titanium pinacolate is a ketone dianion and supports a nucleophilic rather than a radical mechanism for the C-C coupling step of aromatic ketones [267]. This mechanism was supported by quantum mechanical calculations [268]. 

U2CI9 and UCU, which were then reduced at lower potentials [274]. 

Similar treatment of aromatic ketones PhCOR with the ua4-Li(Hg) system afforded a mixture of the corresponding pinacol and the keto alcohol resulting from 

Whatever the amalgam, the first intermediate was 179 resulting from dimerization of the ketyl complex 178, which was trapped with PhsSnH the crystal struc- 

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