Synthesis of Nitrogen Heterocycles by the Ring Opening of Pyridinium Salts

✍ Scribed by Aaron M. Kearney; Christopher D. Vanderwal

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 117 KB
• Volume: 45
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.200602996

✦ Synopsis

The ring-opening reaction of pyridinium salts dates back over a century to the pioneering work of Zincke and König. [1] Activation of pyridines as their pyridinium salts renders the heterocycle electrophilic at the 2-and 4-positions and enables a diverse range of productive chemistry, with or without ring opening. [2] Treatment of appropriately activated pyridinium salts, such as 1 (Scheme 1), with primary amines leads to the formation of new pyridinium salts (2), whereas the use of secondary amines cleanly affords the products of ring opening. [3,4] Both the ring-opening process and the product 5amino-2,4-pentadienals (3), [4a] now known as Zincke alde-Scheme 1. Proposed use of tethered nucleophiles to induce pyridinium ring opening leading to substituted heterocycles. A = generic activating group.