Synthesis and Reactions of Strained Hydrocarbons Possessing Inverted Carbon Atoms. Tetracyclo[3.3.1.1^3.7.0^1.3]decanes

Tetracyclo[3.3.1.1^3.7.0^1..3]decane (i.e., 1,3-dehydroadamantane or DHA) and its 5,7-dimethyl derivative may be synthesized from the corresponding 1,3-dibromoadamantane compounds with sodium–potassium alloy in ether or heptane. These highly strained cyclopropyl compounds are very reactive towards free radical and electrophilic reagents. They homopolymerize 140–160° to thermally resistant, insoluble materials and spontaneously copolymerize with oxygen in solvents at room temperature. Reaction with bromine in ether at −70° yields an intermediate bromoadamantyloxonium tribromide which decomposes to 1-bromo-3-ethoxyadamantane on warming. Other rapid reactions of these strained 1,3-dehydroadamantanes are reported.