Size-selective synthesis of [9]–[11] and [13]cycloparaphenylenes

Abstract

The first size-selective synthesis of [9]- [11] and [13]cycloparaphenylenes (CPP) has been achieved by strategically utilizing cis-1,4-diphenylcyclohexane-1,4-diyl as the key terphenyl-convertible L-shaped unit. To access the designed triangular or rectangular macrocyclic precursors, we utilized palladiumcatalysed C-B/C-Br cross-coupling (Suzuki-Miyaura coupling) and/or nickel-mediated C-Br/C-Br coupling. We also established step-economical routes to [14] and [16]CPP using nickel-mediated C-Br/ C-Br coupling. The final aromatization steps toward CPPs were accomplished with NaHSO 4 . Thus, combined with our previous size-selective synthesis of [12] and [14]-[16]CPP, we completed our sizeselective synthesis of [9]-[16]CPP. The successful size-selective syntheses of [n]CPPs speak well for the flexibility and reliability of our strategy using a cyclohexane ring.

Extraordinary Transformations to Achieve the Synthesis of Remarkable Aromatic Compounds

“…[18] The first elimination is a normal dehydrohalogenation, but the second is extraordinary in that it occurs with concomitant opening of the three-membered ring and enjoys the benefit of both strain relief and the formation of a new benzene ring. This reaction is evidently equal to the enterprise of converting the next lower homologue 15 into [4]metacyclophane (16), but the product is not stable as suggested by the isolation of its Dewar benzene valence isomer 17 (along with some other hydrocarbons). [19] The ability of the reaction to generate a benzene ring that would rather not be a benzene ring underscores its considerable power.…”

“…In contrast to bridged Dewar benzene 17, which was obtained as an unwanted product in Bickelhaupt's attempted syntheses of [4]metacyclophane (16), a substantial number of Dewar benzenes have been synthesized intentionally and exploited in the synthesis of small cyclophanes. Indeed, even 17 could be pushed back in the direction of [4]metacyclophane (16), but only products arising from dimerization of the presumed cyclophane were ever isolated.…”

“…Indeed, even 17 could be pushed back in the direction of [4]metacyclophane (16), but only products arising from dimerization of the presumed cyclophane were ever isolated. [30] The success of the Dewar benzene approach relies upon its bent shape, kinetic stability and high strain energy.…”

“…hydrogenated analogs of 12. [16] Here, the aromatization reaction is performed using ptoluenesulfonic acid under relatively harsh conditions (150°C, microwave irradiation) and presumably involves a double dehydration reaction coupled with dehydrogenation. The smallest CPP synthesized using this methodology is [7]CPP.…”

Selective and Gram-Scale Synthesis of [6]Cycloparaphenylene

“…1-8 Since the first syntheses of [9]CPP, [12]CPP, and [18]CPP by Bertozzi and co-workers in 2008, 9 significant progress toward the synthesis of CPPs and CPP analogues of various sizes has been made by Jasti, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and their respective co-workers, as well as by other research groups. [36][37][38][39][40][41][42][43] Consequently, several unique properties of CPPs, such as their size-dependent photophysical 44-50 and redox properties 31,51-55 and their size-complementary host-guest chemistries, 56-59 have been revealed.…”