Semipinacol rearrangement
The semipinacol rearrangement is a
1,2-shift. Simultaneously with the shift, a pi bond forms from the oxygen to carbon, assisting in driving the migrating group off its position. The result is a ketone or aldehyde.[1] In another definition all semipinacol rearrangements "share a common reactive species in which an electrophilic carbon center, including but not limited to carbocations, is vicinal to an oxygen-containing carbon and can drive the 1,2-migration of a C–C or C–H bond to terminate the process, generating a carbonyl group ".[2]
The rearrangement reaction can be classified into 4 types. Type 1 concerns all 2-heterosubstituted alcohols. Substrates in type 2 rearrangements are
acyloin rearrangements
.
While similar to the pinacol rearrangement, the semipinacol rearrangement differs from the pinacol rearrangement in that the cation is not formed from a vicinal 1,2-diol. With diazoalcohols the reaction is known as the Tiffeneau–Demjanov rearrangement.
References
- ^ Strategic applications of named reactions in organic synthesis: background and detailed mechanisms László Kürti, Barbara Czakó 2005