Synthesis and stereochemical resolution of a [6]pericyclynedione: Versatile access to pericyclynediol precursors of carbo-benzenes

The synthesis of quadrupolar tetraphenyl-carbo-benzene derivatives is envisioned through the corresponding tetraphenyl-tetramethoxy-[6]pericyclynedione last-but-one precursor. The latter was thus prepared in 9 steps and 7% overall yield via the corresponding [6]pericyclynediol, itself obtained by a [8 + 10] ring formation process between a C8 octatriyne dinucleophile and a C10 decatriynedial dielectrophile. In the search for even shorter alternative accesses, the preparation and attempted uses of the corresponding C10 decatriynediol and diethyl decatriynedioic diester are also described. While the pericyclynediol possesses 14 diastereoisomers proving unseparable, the pericyclynedione possesses five diastereoisomers only that could be resolved by semi-preparative HPLC techniques. Reaction of the pericyclynedione with trimethylsilylethynylmagnesium bromide afforded the alkynyl-[6]pericyclyneketol mono-adduct in 22% yield, along with the corresponding [6]pericyclynediol bis-adduct in 43% yield. One of the 14 diastereoisomers of the latter could be separated by column chromatography, and its configuration could be assigned to one of only two possibilities in accordance with the observed number of non-equivalent 1H and 13C NMR signals. Since a regioisomer of the dialkynyl-[6]pericyclynediol bis-adduct was shown to undergo “efficient” reductive aromatization, these results demonstrate the potential value of the pericyclynedione as a pivotal precursor of p-disubstituted tetraphenyl-carbo-benzenes.