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

Abstract

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 þ 10] ring formation process between a C 8 octatriyne dinucleophile and a C 10 decatriynedial dielectrophile. In the search for even shorter alternative accesses, the preparation and attempted uses of the corresponding C 10 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 semipreparative 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 1 H and 13 C 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-carbobenzenes.

1,4‐Dialkynylbutatrienes: Synthesis, Stability, and Perspectives in the Chemistry of carbo‐Benzenes

“…In the absence of the intense TIPS signals of 2 at d = 1.21 ppm, two signals at d = 3.68 and 3.73 ppm in a 60:40 ratio were assigned to the acetylenic protons of the cis and trans isomers of 1 (without configurational assignment). All attempts to record a clean 13 C NMR spectrum of 1 failed due to its poor stability in sufficiently concentrated solutions. Nevertheless, 1 could be kept for a few days at 4 8C in pentane (approximately 3 mm, obtained after filtration through silica gel with pentane as eluent).…”

“…The triyne diether 7 was then targeted from the known bisA C H T U N G T R E N N U N G (silyl)-protected triynediol 10, which was readily prepared by addition of two equivalents of lithium trimethylsilylacet-A C H T U N G T R E N N U N G ylide to the diketone 8. [13] Cleavage of the trimethylsilyl groups of 10 led to the formation of the bisA C H T U N G T R E N N U N G (terminal) triyne 11 in 79 % yield. However, the simultaneous quadruple methylation of 11 proved to be problematic.…”

“…In contrast, the influence of the R substituents for a given cap E (= TIPS) gives rise to a marked variation in the 13 C NMR shifts over a range of more than 10 ppm (Table 2, entries 4-7). For p-cross-conjugated substituents (R = Ph or C C-TIPS), the butatrienic sp carbon atoms thus resonate at d = 149-151 ppm (Table 2, entries 4 and 7), whereas a selectron-withdrawing substituent (R = CF 3 ) induces an expected deshielding and a consequent shift to d = 158.5 ppm (Table 2, entry 5).…”

“…According to the data listed in Table 2, the influence of the cap E is indeed negligible, with 13 C NMR chemical shifts between d = 148.0 and 149.0 ppm for the same substituent R = Ph (Table 2, entries 2 to 4).…”

Towards graphyne molecular electronics

“…1; prepared in nine steps and 7% yield as described in ref. 2) 43 (150 mg, 0.22 mmol) in THF (10 ml) at 0°C. The stirring was maintained for 2 h at 0°C, and then overnight at room temperature.…”