Highly regio- and stereoselective addition of aminoenones to 2-substituted 3-nitro-2H-chromenes. Unexpected synthesis of 5-(trifluoromethyl)-5H-chromeno[3,4-b]pyridines

Reactions of 2-R-3-nitro-2H-chromenes (R=CF3, CCl3, Ph) with aminoenones derived from acetylacetone and cyclic amines (morpholine, piperidine) proceed diastereoselectively to give mainly cis–trans-2,3,4-trisubstituted chromanes as a result of nucleophilic addition of the vinylogous β-methyl group at the C-4 atom of the chromene system. From these compounds, under acidic conditions, 4-acetoacetonyl-3-nitrochromanes and 5H-chromeno[3,4-b]pyridines, depending on the substituent at the 2-position, were obtained in moderate to good yields. Similar results, except for the synthesis of 5H-chromeno[3,4-b]pyridines, were obtained by replacing acetylacetone with benzoylacetone. The stereochemistry of the products was established by X-ray diffraction analysis.

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