The Nazarov reaction of 1-acryloyl-1,3,5-cycloheptatriene; a novel synthetic pathway from 1,3,5-cycloheptatriene to dihydro-1(2H)-azulenone

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.