Rearrangements to Electron-Deficient Nitrogen and Oxygen Centers

Rearrangements to Electron-Deficient Nitrogen and Oxygen Centers Migration of an alkyl group was discussed in Section 6.2.1.2. The well-known 

The nitrenium ion rearrangement is characteristic of bicyclic N-haloamines catalyzed by Ag+ ions. As shown in Equation (6.151), it again involves a transition state with a pentacoordinate carbon.  

In a recent example the singlet nitrenium ion 155 derived from isoxazoli-dines undergoes rearrangement via aryl migration with the participation of the pentacoordinate intermediate [Eq. (6.152)]  

Ar = Ph, 4-CIC6H4, 4-EtOC6H4, 4-Me2NC6H4, 4-NO2C6H4 = Ph, 4-MeOC6H4, 4-CNC6H4 

In the Baeyer-Villiger rearrangement, ketones are oxidized to esters (or lactones) with peracids or hydrogen peroxide. According to the mecha- 

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