Periselectivity between the [1,4] and [3,3] thermal sigmatropic rearrangements of 2-allyloxypyridine N-oxides

Abstract

Thermal rearrangement of 2-allyloxypyridine N-oxides (4a-c) yields N-allyloxy-2-pyridones (5a-c) and 3-allyl-N-hydroxy-2-pyridones (6a-c). These transformations are shown to be regiospecific and on this basis it is proposed that the reactions involve concerted [1,4] and [3,3] sigmatropic rearrangements. Supporting evidence based on solvent effects, temperature effects, and substituent effects is given.

Development of a New Lewis Acid-Catalyzed Claisen Rearrangement

“…This [3,3]-sigmatropic rearrangement, which involves the conversion of an allyl vinyl ether to an α,β-disubstituted γ,δ-unsaturated carbonyl, generally proceeds with high levels of stereocontrol, securing its widespread use in natural product and medicinal agent synthesis . Activation of this rearrangement has traditionally been accomplished under thermal control; however, significant rate acceleration can be achieved through the incorporation of cationic or anionic charge in the bond reorganization event. Despite its prolific use in chemical synthesis and disposition toward charge acceleration, only two examples of catalytic Claisen variants have been reported .…”

Recent trends in the chemistry of pyridine N-oxide

“…[70][71][72] These transformation are shown to be regiospecific and the reactions involve concerted [1,4] and [3,3] sigmatropic rearrangements.…”