Methylarene-Based PAH Synthesis via Domino Cyclization of 1,1-Difluoro-1-alkenes

Abstract

Polycyclic aromatic hydrocarbons (PAHs) containing 4–7 benzene rings were synthesized via a methylarene-based protocol. Trimethyl[2-(trifluoromethyl)allyl]silane was electrophilically benzylated with Ar1CH2Br (prepared from Ar1CH3) to afford 2-trifluoromethyl-1-alkenes that were in turn nucleophilically benzylated with Ar2CH2Li (prepared from Ar2CH3) through an SN2′-type reaction to produce 1,1-difluoroethylenes, which are cyclization precursors bearing two 2-arylethyl groups. Magic acid efficiently promoted the domino Friedel–Crafts-type cyclization of these precursors, followed by dehydrogenation that enabled the connection among two aryl groups (Ar1 and Ar2) by forming two benzene rings between them, facilitating the synthesis of the desired higher-order PAHs. With the proposed protocol, the combination of even a limited number of methylarenes can yield a variety of PAHs in diverse configurations.

Construction of Substituted [4]Acene Frameworks Based on Double Cationic Cyclizations of Fluoroalkenes

“…Notably, chlorinated 13f and brominated 13g underwent hydrodehalogenation as well as dehydrogenation by Pd/C (not shown). 24 Although p -chloranil (tetrachloro- p -benzoquinone) was not effective, triphenylmethylium tetrafluoroborate (Ph 3 CBF 4 ), which was effective in our previous synthesis of angular PAHs, 10c provided 5g from 13g in a moderate yield. The yields of halogenated [4]acenes 5f and 5g were increased by the use of trityl cations, which were generated from triphenylmethyl alcohol in refluxing trifluoroacetic acid.…”

Multiple-fold C–F bond functionalization for the synthesis of (hetero)cyclic compounds: fluorine as a detachable chemical handle

“…Based on designing distinct reaction manifolds that harness a consecutive vinylic C-F bond breaking, a practical function of gem-difluoroalkene as a readily available onecarbon synthon was previously found by Ichikawa and coworkers (Scheme 59). 106,107 The research highlighted that polycyclic aromatic hydrocarbons (PAHs) could be easily prepared by treating functionalized gem-difluoroalkenes bearing two tethered aryl moieties with magic acid (FSO 3 H•SbF 5 ) or TiF 4 in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). A plausible reaction mechanism revealed that the protonation of difluoroalkene 59-1/monofluoroarene 59-4, leading to fluorine-stabilized cationic species 59-3 and arenium ion 59-5, is more likely to be a key process in the formation of the final product.…”