The title compound was prepared as part of an effort to accomplish the first synthesis of a cis-10b,10c-dimethyl-10b,10c-dihydropyrene according to our ''tethered metacyclophane'' strategy. The 11-step synthesis starting from 2,4,6trimethylphenol had an overall yield of 4.1%. An X-ray crys-
The 10b,10c-dihydropyrene skeleton has attracted a great deal of theoretical and experimental interest due to the aromatic character of its 14 π-electron periphery. [1] Since the parent system 1 is prone to the loss of hydrogen to give pyrene, most of the work in this area has been conducted on analogues that bear substituents at the internal (10b and 10c) positions. By far the most prominent of these are the 10b,10c-dimethyl-10b,10c-dihydropyrenes (DMDHPs) 2.
DMDHPs are normally prepared by the valence isomerization of the corresponding [2.2]metacyclophanedienes 3 (Scheme 1), which exhibit syn/anti conformational isomerism. Since the valence isomerization is stereospecific, the anti-[2.2]metacyclophanedienes become trans-DMDHPs and the syn-[2.2]metacyclophanedienes are transformed into cis-DMDHPs. The ''cyclophane route'' that is generally used for the synthesis of the [2.2]metacyclophanedienes leads predominantly to the formation of anti conformers and hence trans-DMDHPs. As a result, cis-DMDHPs are not easily accessible compounds and they are not well studied experimentally.
We recently demonstrated how the presence of a third bridge (a tether) during the synthesis of the [2.2]metacyclophanediene system could ensure the formation and maintenance of only the syn conformation and thus lead exclusively to the cis isomer of the DMDHP. cis-Dimethyldihydropyrenophane 4 was prepared by this strategy and its Xray crystal structure was determined, thus providing the first experimentally derived structural data for the cis-DMDHP skeleton.