Selective Access to 2,3,6‐Trisubstituted Pyridines

What is it about?

An efficient sequential one-pot, two-step pseudo-four-component reaction between 3/4-methyl N-sulfonyl ketimines with 3-chloropropiophenones triggered by DIPEA/NaHCO3 as a cooperative base and subsequent aza-cyclization using NH4OAc is reported. This transition-metal-oxidant-free technique concocts new C−C/C=C/C=N−C bonds selectively, guaranteeing acceptable yields of 2,3,6-trisubstituted pyridines possessing ortho-hydroxyaryl/benzenesulfonamide and propiophenone moieties at C2 and C3 positions, respectively. Interestingly, while replacing methyl-substituents with straight alkyl chains of N-sulfonyl ketimines, only a monoalkylation reaction happened with in situ-generated vinyl ketones to deliver promising yields of 3-picoline derivatives. Moreover, the synthetic transmutation of prepared pyridine derivative led to several important classes of pyridocoumarin, 5H-chromenopyridine, and di(pyridin-3-yl) methane derivatives.

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Why is it important?

Efficient de novo access to 2,3,6-trisubstituted pyridines was successfully synthesized through a mono- or dialkylation reaction between 4/3-alkyl-N-sulfonyl ketimines with 3-chloropropiophenones using DIPEA/NaHCO3 as a cheap cooperative basic system and subsequent aza-cyclization in the presence of NH4OAc under an air.