Ring expansion (chemistry)

This article deals with the concept of ring expansion in chemistry; for the mathematical concept of ring expansion, see lower and upper ring .

As ring expansion such chemical reactions are referred to, which extend an existing ring around a member or several members. This usually takes place via a cationic intermediate . The ring expansion is the counterpart to the ring narrowing (e.g. the Favorskii rearrangement ).

Reactions

Ring expansion through a Tiffeneau reaction - a five-membered ring becomes a six-membered ring

Well-known ring expansion reactions are, for example, the Beckmann rearrangement , the Tiffeneau ring expansion and the Baeyer-Villiger reaction .

The Beckmann rearrangement , in which cyclic ketones are rearranged to lactams , is the most important industrially. It is used for the synthesis of ε- caprolactam, a raw material for polyamide production. The peroxidic Baeyer-Villiger reaction is used to lactonize cyclic ketones. In the Tiffeneau reaction, a methylene group is formally inserted into cyclic ketones .

If ethylcyclobutane ( 1 ) is heated with aluminum chloride (AlCl ₃ ), methylcyclopentane ( 2 ) is formed with ring expansion :

literature

• Eric J. Kantorowski, Mark J. Kurth: Expansion to Seven-Membered Rings . In: Tetrahedron . 56, No. 26, June 2000, pp. 4317-4353. doi : 10.1016 / S0040-4020 (00) 00218-0 .

Individual evidence

1. ↑ Entry on ring reactions. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
2. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 220, ISBN 3-342-00280-8 .