On the cyclization to the elusive amino‐4H‐pyran ring some new facts

The reaction of 2‐indolinone (1) with arylidenemalononitriles (2) or benzylidenecyanoacetamide (9) yields the Michael adducts 3, 10 and the spiro compound 4a. No cyclization to a 4H‐pyran ring is achieved. Similar results are obtained from the unsaturated lactone 11 and the carbonyl compound 13. In contrast, 1,3‐cyclohexanedione (15) leads to the fused 2‐amino‐4H‐pyran 16 upon reaction with benzylidenemalononitrile (2).