Methylated multibridged [2n]cyclophanes. All alternate synthesis of [26](1,2,3,4,5,6) cyclophane (superphane)

A sequence of formylation followed by a carbene insertion reaction has led to the stepwise introduction of additional ethano bridges into 4,5,7,8- tetramethyl 2₂](1,4)cyclophane ($\text{1}$), providing syntheses of 5,7,8-trimethyl- 2₃](l,2,4)cyclophane ($\text{6}$), a mixture of 5,8-dimethyl2₄(1,2,4,5)cyclophane ($\text{10}$) and 5,7-dimethyl2₄(1,2,3,5)cyclophane ($\text{11}$, and-4-methyl2₅](1,2,3,4,5)-cyclophane ($\text{14}$). This route to $\text{14}$ completes a formal eight-step synthesis of 2₆](1,2,3,4,5,6)cyclophane ($\text{15}$, superphane) with an overall yield of 17%. A Birch reduction of $\text{6}$ readily gave 12,15-dihydro-5,7,8-trimethyl2₃](1,2,4)-cyclophane ($\text{7}$) in 85% yield.