Medium‐Sized Cyclophanes, 25. Bromination of [2.<i>n</i>]Metacyclophan‐1‐enes and Isolation of Two Isomers of 1‐Bromo[2.<i>n</i>]metacyclophan‐1‐enes

Abstract

Abstract Bromination of dimethyl[2.3]metacyclophan‐1‐ene ( 1b ) with bromine affords the cis adduct 6b resulting from the addition to the bridging double bond; a similar reaction of dimethyl[2.4]metacyclophan‐1‐ene ( 1c ) gives a mixture of the cis and trans adduct formed by the addition to the bridged double bond along with the products containing a brominated internal methyl group. On the other hand, bromination of dimethy1[2. n ]metacyclophan‐1‐enes ( 1 ) with benzyltrimethylammonium tribromide affords exclusively the product of the cis addition 6 to the bridged double bond. Treatment of [3.2]metacyclophane 6b with potassium tert 1‐butoxide in refluxing t BuOH for 1 h gives the dehydrobrominated product ( E )‐ 8b in 95% yield; a similar reaction of [4.2]metacyclophane 6c furnishes two isomers, ( E )‐ 8c and ( Z )‐ 8c , of 1‐bromo[2.4]1‐metacyclophan‐1‐ene along with [2.4]metacyclophan‐1‐one 9c in 20% yield. The characterization and the reaction pathway of these products are discussed.