Synthesis and demethylation of 4,22-dimethoxy[2.10]metacyclophan-1-yne with BBr ₃ to afford a novel [10](2,9)-5a,11a-benzofuro-5a-bora-11- bromochromenophane

4,22-Dimethoxy[2.10]metacyclophan-1-yne was prepared by bromination of [2.10]metacyclophan-1-ene followed by the dehydrobromination of the bromine adduct with KOBu-t. Treatment of 4,22-dimethoxy[2.10]metacyclophan-1-yne with BBr ₃ in CH ₂Cl ₂ at room temperature led to the demethylation and a successive intramolecular cyclization reaction to afford a novel [10](2,9)-5a,11a-benzofuro-5a-bora-11-bromochromenophane in good yield. Similar treatment of a mixture of the corresponding meso-and dl-1,2-dibromo-4,22-dimethoxy[2.10]metacyclophane with BBr ₃ in CH ₂Cl ₂ under the same conditions described above afforded cis-4b,9b-dihydro[10]benzofuro[3,2-b]benzofuranophane in 83% yield.