The mechanism of the Rappe Rearrangement – a stereochemical investigation using Density Functional Theory
Author(s)
Sommer, Toby
Rzepa, Henry
Type
Journal Article
Abstract
Since it was first described in the 1950s, there has been no explanation of the extraordinarily high selectivity for the formation of the thermodynamically less stable cis-2-alkenoic acids from the treatment of α,α′-dibromoketones with aqueous base. Very early on, it was suggested that such specificity must arise via “concerted processes” but without elaboration. Provided here is a detailed mechanistic description of the reaction based on computational insight, identifying a stereospecific first step for the ring closure to a 3-ring cyclopropanone, which follows Woodward–Hoffmann rules for a two-electron allylic cation, accompanied by departure of a bromine atom in an SN2-like process. The stereochemistry established in this step persists in the second step, which involves ring opening of the 3-ring to give a cis-2-alkenoic acid. Other mechanistic pathways have higher energies. With this new understanding, further synthetic applications of the Rappe Rearrangement are suggested.
Date Issued
2025-07-04
Date Acceptance
2025-05-28
Citation
Journal of Organic Chemistry, 2025, 90 (26), pp.9037-9045
ISSN
0022-3263
Publisher
American Chemical Society
Start Page
9037
End Page
9045
Journal / Book Title
Journal of Organic Chemistry
Volume
90
Issue
26
Copyright Statement
Copyright © 2025 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY 4.0 .
License URL
Identifier
10.1021/acs.joc.5c00726
Publication Status
Published
Date Publish Online
2025-06-20