Carbonyl compounds intermolecular pinacol coupling reactions

In a related reaction, a stannylene transfer reagent will bring about the intermolecular pinacol coupling of a carbonyl compound.69... 

Intermolecular coupling Many papers on hydrodimerization of aromatic carbonyl compounds have appeared indicating the importance of this reaction. The rac/meso ratio for the pinacolization of acetophenone in aqueous ethanol ranges between 0.9 and 1.4 in acidic medium and between 2.5 and 3.2 in basic medium. The diastereoselectivity is independent of the cathode material mercury, tin, or copper. Electrolysis conditions such as current density, potential, or current-controlled electrolysis also do not influence the diastereoselectivity. The same holds for propiophenone. For benzaldehyde, the rac/meso ratio is 1.1 to 1.2 in acidic as well as in basic media [283]. In the presence... 

Coupling reactions of indoles and carbonyl compounds (either intra- or intermolecularly) have been described. This is a new method for hydroxylation at the C2 position of indole (Scheme 36). The role of HMPA is crucial to prevent reduction or pinacolic coupling of aromatic carbonyl compounds [80]. 

---