Amine Exchange and Unexpected Ring-Opening Reactions of Pyranone Derivatives: Synthesis of 3-Amino-Substituted Oxonaphthopyran-carbaldehydes and Tetrahydropyrimidinethanones as New Potential Oligonucleotide Stabilization Agents

3‐[(3‐Aminopropyl)amino]‐1‐oxo‐1H‐naphtho[2,1‐b]pyran‐2‐carbaldehyde (10) was synthesized by nucleophilic substitution reaction of 2‐(3‐dimethylamino)‐1‐oxo‐1H‐naphtho[2,1‐b]pyran‐2‐carbaldehyde (9) and the monoprotected propane‐1,3‐diamine. The reaction with the unprotected reagent led to the unexpected 1‐(2‐hydroxynaphthalen‐1‐yl)‐2‐(tetrahydropyrimidin‐2(1H)‐ylidene)ethanone (6). Extension of this reaction to chromone 16 gave 1‐(2‐hydroxy‐3‐isopropyl‐6‐methylphenyl)‐2‐(tetrahydropyrimidin‐2(1H)‐ylidene)ethanone (7). The X‐ray crystal structures of 6 and 7 were also determined.