Beckmann Rearrangement and Beckmann Fragmentation

AbstractThe rearrangement of an oxime to its corresponding amide in the presence of an acid and is generally known as the Beckmann rearrangement. The oxime is also formed by the reaction of a ketone with hydroxylamine. The conversion of cyclohexanone oxime into e‐caprolactam is known to be an important component for the fabrication of nylon 6. The Beckmann rearrangement of oxime derivatives proceeds stereospecifically, and the stereo‐configuration of the migrating group is retained. This rearrangement has been applied to the construction of a variety of nitrogen‐containing compounds. Certain oximes, those having a quarternary carbonantito the hydroxyl, have been reported to undergo the rearrangement to form nitriles instead of amides. This type of transformation is called the Beckmann fragmentation, which has been used in modification of steroids. Other oximes, such as the bridged bicyclic ketoximes and oximes with an electron‐donating substituent at the α‐carbon, also undergo fragmentation.