Synthesis and ring-opening reaction of novel 1,3-dehydroadamantanes possessing phenyl and alkoxyl substituents

A series of novel 1,3-dehydroadamantanes (DHAs) possessing phenyl or alkoxyl substituents, such as 5-phenyl-1,3-dehydroadamantane, 5-butyl-7-phenyl-1,3-dehydroadamantane, 5-methoxy-1,3-dehydroadamantane, 5-butoxy-1,3-dehydroadamantane, 5-butyl-7-methoxy-1,3-dehydroadamantane, and 5-butoxy-7-butyl-1,3-dehydroadamantane were synthesized and subjected to react with acidic compounds. 1,3-Dibromoadamantanes carrying phenyl or alkoxyl substituents were converted into the corresponding DHAs via the intramolecular Wurtz-type coupling reactions with lithium metal in THF in 23–62% yields. Ring-opening reactions of DHAs readily occurred with acetic acid or methanol under acidic conditions to form various 1-acetoxyadamantanes or 1-methoxyadamantanes containing phenyl or alkoxyl groups. The resulting 1-butyl-3-methoxy-5-phenyladamantane, 1-acetoxy-3-butyl-5-phenyladamantane, 1-acetoxy-3-butyl-5-methoxyadamantane, 1-acetoxy-3-butoxy-5-butyladamantane, and 1-butoxy-3-butyl-5-methoxyadamantane possessed stereogenic center. The high reactivity of the inverted 1,3-carbon–carbon σ-bond in DHAs toward the acidic compounds indicated the high electron density, which was supported by the sp2 character of cyclopropane rings in DHAs estimated by JC–H coupling constants in the 13C NMR analyzes.