Studies on Sequential Claisen Rearrangement: Charge‐Accelerated [3,3]‐Sigmatropic Rearrangement Leading to Polyheterocycles

A number of quinolone‐annulated pentacycles have been regioselectively synthesized in 90–95% yields by sequential Claisen rearrangements. The second synthesis is anhydrous AlCl3‐catalyzed charge‐accelerated aromatic Claisen rearrangement of 1‐aryloxymethyl‐6‐alkyl‐3H‐pyrano[2,3‐c]quinolin‐5(6H)‐ones in dichloromethane at rt for 5–10 min. The precursors were synthesized by the thermal [3,3]‐sigmatropic rearrangement of the corresponding ethers.