Beilstein J. Org. Chem.2023,19, 820–863, doi:10.3762/bjoc.19.62
pyridine syntheses have relied on the condensation of carbonyl compounds and amines for a very long time [11]. The classical methods for the synthesis of functionalized pyridine include the Hantzsch pyridine synthesis and the Bohlmann–Rahtz synthesis (Scheme 1a and b). Furthermore, alternative
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Graphical Abstract
Figure 1:
Representative examples of bioactive natural products and FDA-approved drugs containing a pyridine ...
Beilstein J. Org. Chem.2013,9, 1957–1968, doi:10.3762/bjoc.9.232
Microwave Technology Ltd, 2 Middle Slade, Buckingham, MK18 1WA, UK 10.3762/bjoc.9.232 Abstract The Bohlmann–Rahtz pyridine synthesis and the Hantzsch dihydropyridine synthesis can be carried out in a microwave flow reactor or using a conductive heating flow platform for the continuous processing of
material. In the Bohlmann–Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield. Furthermore, 3
-substituted propargyl aldehydes undergo Hantzsch dihydropyridine synthesis in preference to Bohlmann–Rahtz reaction in a very high yielding process that is readily transferred to continuous flow processing.
Keywords: Bohlmann–Rahtz; continuous flow processing; ethynyl ketones; flow chemistry; Hantzsch
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Graphical Abstract
Scheme 1:
Mesoscale production of heterocycles in a continuous flow microwave reactor [44-46].