N‐Oxides as Control Element for the Direction of a Sigmatropic Rearrangement: Application as a Switch for Fluorescence

A simple change of solvent swaps the predominance of each of these two isomers: The high affinity of the N-oxide moiety for water and other hydroxylated solvents is responsible for this unprecedented ‘Reverse Meisenheimer Rearrangement’. The N-oxide fragment thus serves as an ‘on/off’ switch for fluorescence and possibly several other applications.

Abstract

An exceptional level of control over the direction of the (2,3)-sigmatropic rearrangement between N-oxides and alkoxylamine is achieved by simply changing the solvent in which they are dissolved. Protic solvents like water, methanol and hexafluoroisopropanol favour the N-oxide form, while other solvents like acetone, acetonitrile and benzene favour the alkoxylamine. The reaction temperature and nature of the substituents on the alkene affect the rate of rearrangement. A N-oxide fragment was attached to two fluorescent molecules and acted as an on/off switch for their fluorescence. The conversion of alkoxylamines into the corresponding N-oxides has not previously been described and is here termed the ‘Reverse Meisenheimer Rearrangement’.

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