The Nazarov Reaction of 1‐Acryloyl‐1,3,5‐cycloheptatriene; a Novel Synthetic Pathway from 1,3,5‐Cycloheptatriene to Dihydro‐1(2H)‐azulenone

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The title compound, 1‐acryloyl‐1,3,5‐cycloheptatriene (3), was prepared from 1,3,5‐cycloheptatriene in four steps, and subsequently its Nazarov cyclization of 3 was studied in order to develop a novel synthetic pathway to dihydro‐1(2H)‐azulenone. While the reaction of 3 in sulfuric acid afforded 1‐tetralone (5) in a low yield, the reaction in a mixture of phosphoric acid and formic acid at room temp. produced 3,8‐dihydro‐1(2H)‐azulenone (6) and 3,3a‐dihydro‐1(2H)‐azulenone (7) in yields of 46 and 13% respectively. Using stannic chloride as the acid in the reaction gave 6 and 7 in a slightly better combined yield.