crude diketone 9a was treated with o-phenylenediamine in ethanol at room temperature for 24 h to afford in almost quantitative yield the desired [2.2]metacyclophane 11 having a quinoxaline skeleton. Similarly, in the case of [2.3]- and [2.4]metacyclophanes, Swern oxidation of the trans-diols trans-4b,c also afforded the desired diketones 9b,c in quantitative yields as stable yellow prisms.
McMurry cyclisation of 1,n-bis(3-formyl-2-methoxyphenyl)alkanes afforded syn-dimethoxy[2.n]metacyclophan-1-enes, in which cis-addition of bromine to the bridged double bond in CH2Cl2 was observed.