The Development of Synthetic Routes to 1,1,n,n‐Tetramethyl[n](2,11)teropyrenophanes

Abstract

A concise synthetic approach to 1,1,n,n‐tetramethyl[n](2,11)teropyrenophanes has been developed. It involves the construction of triply‐bridged pyrenophanes, during which the three bridges are installed successively using Friedel‐Crafts alkylation, Wurtz coupling and McMurry reactions. At the same time, the innate regiochemical preferences of pyrene toward electrophilic aromatic substitution are relied upon to control the substitution pattern. A cyclodehydrogenation reaction is then employed to generate the teropyrene system directly in a nonplanar conformation. The crystal structure of 1,1,7,7‐tetramethyl[7](2,11)teropyrenophane was determined and the teropyrene system was found to have an end‐to‐end bend angle of 177.9°.

Gram‐Scale Synthesis of the 1,1,n,n‐Tetramethyl[n](2,11)teropyrenophanes

“…The aromatic signals of 5 d appear at δ 8.90 (H a ), 8.64 (H b ), 7.88 (H c ) and 7.62 ppm (H d ). These signals are all at lower field ( Δδ =0.08–0.13 ppm) than those of the corresponding protons in 5 c , [13a–c] which is in line with the previously observed trend that the aromatic signals all move to higher field with increasing bend in the teropyrene system. The highest field protons in the bridge resonate at δ −0.46 ppm, which compares with δ −1.00, −0.66 and −1.15 ppm for 5 c , 5 b and 5 a , respectively [13a–c] …”

“…The ß angles [26] are 4.0° and 4.5°. As observed in the other teropyrenophanes 5 a – c , the bend angle of the central pyrene system ( θ 2 =81.0°) in 5 d is larger than those of the two flanking pyrene systems ( θ 1 =57.6° and θ 3 =63.6°), but the differences in magnitude between them are smaller than those in 5 a – c [13a–c] . Nevertheless, the teropyrene system of 5 d still has a semi‐elliptical profile rather than a semi‐circular one.…”

“…Initial work aimed at the synthesis of synthetically useful amounts of the teropyrenophanes 5 a – c involved direct scale‐up of the existing Wurtz/McMurry route (via 7 a ), [13b,c] but this proved to be problematic from the outset. Ultimately, almost every step of the synthesis had to be modified to accommodate scale‐up.…”

A Highly Congested Dioxapyrenophane from an Attempted Synthesis of the Highly‐Strained 1,1,6,6‐Tetramethyl[6](2,11)teropyrenophane

“…[3] The aromatization-based methodology that was employed to generate it can thus be viewed as quite powerful. Upon moving to pyrene, the next member of the ropyrene series of PAHs, [4] the situation is similar. An aromatization-based methodology is used to furnish the bent pyrene system and it smoothly affords [8](2,7) pyrenophane (2 c) and [7](2,7)pyrenophane (2 b) as indefinitely stable compounds.…”

“…In the case of the [n] paracyclophanes, the limit of stability lies at [6]paracyclophane (1 c), [1] or arguably [5]paracyclophane (1 b), [2] which exists in equilibrium with its Dewar benzene valence isomer (Figure 1). [4]Paracyclophane (1 a) has never been observed directly, although its fleeting existence has been inferred. [3] The aromatization-based methodology that was employed to generate it can thus be viewed as quite powerful.…”