Palladium‐Catalyzed Pentannulation of Polycyclic Aromatic Hydrocarbons

Abstract

We present a new and versatile one-step synthesis of a series of small molecular chromophores based on cyclopentannulated polycyclic aromatic hydrocarbons (PAH). Easily available pyrene, anthracene, and perylene bromides serve as starting materials for the reactions. The formation of the five-membered ring is achieved by the straightforward palladium(0)-catalyzed carbannulation with various substituted acetylenes. This approach is applicable either to single or multiple annulation procedures leading to hitherto inaccessible PAH topologies. According to the resulting products of the diverse reactions, a mechanistic explanation is proposed. UV/Vis absorption as well as cyclovoltammetric measurements were performed for characterization demonstrating the value of this annulation technique. Optical absorptions of up to 780 nm and absorption coefficients ranging from 8000 to 34,000 M(-1) cm(-1) were detected.

Polycyclic aromatic hydrocarbons in the graphene era

“…Garcia-Garibay et al [119,120] reported such reactions based on brominated anthracenes and terminal alkynes. Müllen et al [121] further explored the cyclopentannulation reaction using di-substituted alkynes. The reaction proceeds through the insertion of the alkyne 75 into an arylpalladium species 77, followed by intramolecular electrophilic attack of the resulting alkenylpalladium 78 on anthracene to form a palladacycle intermediate 79 (a type of C-H activation step).…”

Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

“…Another intermolecular reaction involving the use of an alkyne to extend the conjugation of PA Hs is the palladiumcatalyzed pentannulation developed by Müllen and co-workers [73] and popularized by the Plunkett group. [74][75][76][77] This simple reaction allows the creation of af ive-membered ring at the periphery of abrominated acenes or other zigzag-edge PA Hs.…”

Palladium‐Catalyzed Annulation of 9‐Halophenanthrenes with Alkynes: Synthesis, Structural Analysis, and Properties of Acephenanthrylene‐Based Derivatives

“…As reported in the literature, compounds 10 a and 12 a were generated in 76 and 30 % yields, respectively, by using a catalytic system that comprised Pd(dba) 2 (10 mol %; dba=dibenzylideneacetone) and P( o ‐tol) 3 (15 mol %) under highly dilute conditions (ca. 10 −2 M ) in toluene 9. One advantage of our protocol is a reduction in the amounts of solvents used.…”

“…The formal [3+2] annulation of a haloarene with an alkyne is effective for enlarging existing aromatic systems in the synthesis of cyclopentene‐fused PAHs. This synthetic strategy has been utilized in the preparation of acenaphthylenes,7 aceanthrylenes,8 cyclopenta[ cd ]pyrenes, and others 9. However, established palladium‐catalyzed protocols cannot be used to synthesize acephenanthrylene efficiently 9…”