Misc

A conceptually distinct, modern strategy for Baeyer-Villiger oxidation (BVO) was developed. Our novel method involves initial hydration of water to carbonyl compounds, followed by ligand exchange of hypervalent arylbromane on bromane(III) with the resulting hydrate, yielding a new type of activated Criegee intermediate. The intermediate undergoes BV rearrangement and produces an ester via facile reductive elimination of arylbromanyl group, because of the hypernucleofugality. The novel strategy makes it possible to induce selectively the BV rearrangement of straight chain primary aliphatic as well as aromatic aldehydes, which is missing in the classical BVO: for instance, octanal and benzaldehyde afforded rearranged formate esters with high selectivity (>95%) under our conditions, while the attempted their classical BVO produced only carboxylic acids. This firmly establishes the powerful nature of new methodology for BVO.

Hypervalent organoiodanes are one of the most valuable classes of oxidants for use in oxidative transformations of various kinds of functionalities in modern organic synthesis. This microreview provides an overview of the recently developed aryl iodide-catalyzed oxidations, in which hypervalent organoiodanes(III and V) generated in situ serve as the actual oxidants. We also summarize recent attempts to improve the efficiency of recyclable hypervalent organoiodanes in oxidations, updating Togo's and Sakuratani's 2002 review. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.