Synthesis via Transformation of Another Heterocycle

The fiiran derivatives 334 containing a 2-acyl functionality were treated with ammonia at 150 C in a sealed-tube to provide the 3-hydroxy pyridines 335 in low 3delds.  

Treatment of 2//-pyran-2-ones 336 with urea in refluxing pyridine temperature afforded 2-aminopyridines 337 regioselectively  

Pyrylium salts are prone to nucleophilic attack. Reaction of pyiylium salts 339 with ammonia or anunonium salts undergo ring-opening/ring-closing reaction sequences to afford the corresponding pyridine derivatives 340. This reaction was also called the Baeyer pyridine synthesis.  

Reaction of pyrylium salts with hydroxylamines and primary amines 

P-Carbolines are a class of indole alkaloids that are structurally similar to tryptophan, which has been shown to be useful for a variety of neuroscience applications The Baeyer pyridine synthesis was applied for the preparation of the P-carboline derivative ambocart) (346)  

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