Tiffeneau-Demjanov rearrangement semipinacol rearrangements

Selectivity in rearrangement reactions is affected by the electronic nature of both the group that migrates and the group that is left behind. But there is more Stereochemistry is important too. The outcome of diazotization and semipinacol rearrangement (Tiffeneau-Demjanov rearrangement) of this amino-alcohol depends entirely on the diaster eoisomer you start with. There are four diastereoisomers, and we have drawn each one in the only conformation it can reasonably adopt, with the f-butyl group equatorial. 

Semipinacol rearrangements of diazonium salts derived from 2-amino alcohols are sometimes called TIffeneau-DemJanov rearrangements. 

---