DBU-Promoted 6π-Azaelectrocyclization and Hydrogen-Migration to Prepare 6-Alkyl Pyridine N-Oxides from N-Vinyl-α,β-Unsaturated Nitrones

We describe a DBU-controlled 6 pi-azaelectrocyclization of dibenzylideneacetone-derived N-vinyl-alpha,beta-unsaturated nitrones to prepare 6-alkyl pyridine N-oxides in 24-82% yields. Mechanistic studies revealed that DBU had a great impact on the formation of 6-alkyl pyridine N-oxides and served as a base and the carrier of hydrogen sources to in situ reduce C=C bonds. The 6-alkyl pyridine N-oxide was prepared at gram-scales and converted to estrone-derived pyridine and pyrido[2,3-c]carbazole 4-oxide in 46% and 52% yields in two steps, respectively.

Automated summary

A DBU-controlled 6π-azaelectrocyclization was used to prepare 6-alkyl pyridine N-oxides in yields ranging from 24% to 82%. Mechanistic studies showed that DBU played a significant role in the formation of 6-alkyl pyridine N-oxides, acting as a base and a carrier of hydrogen sources.