Ring expansion and ring contraction

Ring expansion with a cyclopropane by nucleophihlic attack (A) and neighboring group donation (B).

The bond migration steps in the Baeyer-Villiger oxidation (A) and the Beckmann rearrangement (B).

Ring contraction through anionic (A), cationic (B), and carbenoid (C) reactive intermediates.

Cyclic compounds, ubiquitous in organic compounds, are chains of atoms are covalently bonded to form a closed ring. These rings are primarily composed of carbon, but can also contain heteroatoms such as nitrogen, oxygen, and sulfur (called heterocycles). In the course of organic synthesis a chemist often needs to form a new or alter an existing ring. By expanding or contracting an existing ring it is possible to access structures that would be difficult to nearly impossible with a single cyclization reaction.

单词	Ring contraction
释义	Ring contraction 英语百科 Ring expansion and ring contraction Cyclic compounds, ubiquitous in organic compounds, are chains of atoms are covalently bonded to form a closed ring. These rings are primarily composed of carbon, but can also contain heteroatoms such as nitrogen, oxygen, and sulfur (called heterocycles). In the course of organic synthesis a chemist often needs to form a new or alter an existing ring. By expanding or contracting an existing ring it is possible to access structures that would be difficult to nearly impossible with a single cyclization reaction.
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Ring contraction

Ring expansion and ring contraction