Geminal-dichromium

The boron-Wittig reaction has been carried out by bis(boryl)methyllithium 309 generated in situ from tris(boryl)-methane 308 (Equation (91 )).469 The geminal dichromium reagent 3 12470 was found to be an excellent alternative yielding 1-alkenylboronic esters 313470-472 with high //w/ -selectivity (Equation (92)). 

The exact mechanistic pathway is not known. However, it is believed that the T-U olefinatlon proceeds via geminal-dichromium intermediates that are nucleophilic and attack the carbonyl compound. The ( )-alkene is formed from the P-oxychromium species. 

Takai, K., Shinomiya, N., Kaihara, H., Yoshida, N., Moriwake, T., Utimoto, K. Transformation of aldehydes into (E)-l-alkenylboronic esters with a geminal dichromium reagent derived from a dichloromethylboronic ester and CrC. Syn/ett 1995, 963-964. 

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