Hantszch synthesis

Hantszch synthesis A reaction of an a-haloketone with a (3-ketoester and NH3 or a primary amine yields substituted pyrrole. 

Substituted furan can be prepared by using the Feist-Binary synthesis, which is similar to the Hantszch synthesis of the pyrrole ring. In this reaction, a-haloketones react with 1,3-dicarbonyl compounds in the presence of pyridine to yield substituted furan. 

The calcium channel blocking dihydropyridine drugs 17, used in the important field of heart disease and easily prepared by the Hantszch pyridine synthesis, are chiral but only just. The molecule does not quite have a plane of symmetry, because there is a methyl ester on one side and an ethyl on the other and because R may not be Me. An important example is amlodipine 18, a best seller from Pfizer, and this is more asymmetrical than some. Nevertheless resolving these compounds is difficult. 

Such a long analysis suggests a daunting synthesis, but the stability of aromatic compounds means that reaction of (20) and (19) gives (15) in one step. All we have to do is to construct (22) by standard C02Et activated methods and combine it with (21) under reducing conditions. Reduction, condensation, decarboxylation all occur together. This is the Hantszch pyrrole synthesis. ... 

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