[8+2] Cycloaddition of 8-oxoheptafulvene with cycloheptatrieneFe(CO)3: synthesis of tricarbonyl[(2,3,4,5-η)-11-acetoxy-1H-cyclohept[a]azulene]iron

8-Oxoheptafulvene reacted with cycloheptatrieneFe(CO)3 by [8+2] cycloaddition to give tricyclo[8.5.0.03,9]pentadeca-3,5,7,11,13-pentaene-2-oneFe(CO)3 (3), which easily reacted with another 8-oxoheptafulvene under the reaction conditions to give four products. One of them was a [2+4] cycloadduct (5) having an uncommon norcaradiene structure. Two products were [8+2] cycloadducts (6 and 7) having a γ-lactone structure. The remaining product was an acylated compound (4). On raising the reaction temperature, the yields of the acylated compound increased. The [1:1] cycloadduct 3 reacted also with acetyl chloride in the presence of triethylamine to give an acetate (12), which was oxidized with o-chloranil to give 11-acetoxy-1H-cyclohept[a]azuleneFe(CO)3 (15).