Bohlmanr-Rahtz pyridine synthesis

What is Bohlmanr-Rahtz pyridine synthesis?

In 1957, Bohlmann and Rahtz developed a method for preparing 2,3,6-trisubstituted pyridines. Bohlmanr-Rahtz pyridine synthesis involved using the Michael addition of acetylenic ketones 1 with enamines 2. The 6-aminoketones 3 are typically isolated and subsequently heated at temperatures exceeding 120 ºC to promote cyclodehydration and generate 4.

Bohlmanr-Rahtz pyridine synthesis
Bohlmanr-Rahtz pyridine synthesis

The mechanism involved in this method shows similarities to that of the Hantzsch protocol, but in this case, the pyridine is directly formed, eliminating the need for the oxidation step required in the Hantzsch pyridine synthesis.

Bohlmanr-Rahtz pyridine synthesis to obtain heterocyclic substituted α-amino acids Baldwin
Bohlmanr-Rahtz pyridine synthesis to obtain heterocyclic substituted α-amino acids

Baldwin utilized the Bohlmann-Rahtz synthesis to obtain heterocyclic substituted α-amino acids, which involved the reaction of alkynyl ketone 5 with 3-aminocrotoyl ester 6 to form Michael product 7, followed by thermolysis to produce pyridyl-β-alanines 8.

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