Photocyclodehydrofluorination

Abstract

Mallory-type photocyclization involves a series of photoreactions of stilbenes, o-terphenyls and related derivatives, which undergo intramolecular cyclization via dihydrophenanthrene intermediates. In typical Mallory photocyclizations, oxidants are usually needed to produce the final phenanthrene-containing product. In the research described here, appropriately fluorinated stilbenes and o-terphenyls undergo ring closure and HF is eliminated. This photocyclodehydrofluorination (PCDHF) reaction is very useful to produce a wide range of selectively fluorinated polynuclear aromatic hydrocarbons that possess a phenanthrene (or heterocyclic analogue of phenanthrene) substructure. These fluorinated products are of great interest in various aspects of the materials science.

Synthesis of Pinpoint‐Fluorinated Polycyclic Aromatic Hydrocarbons: Benzene Ring Extension Cycle Involving Microwave‐Assisted SNAr Reaction

“…(b) These compounds were also accessible from 1,1-difluoroalkenes via ac ationic palladium(II)-catalyzed cyclization (Scheme 1). [5,10,11] As the preparation of the substrates for the indium(III)-catalyzed synthesis of pinpoint-fluorinated PAHs (i.e.,d ifluoroallenes) involvedf luoroarenes as starting materials, we envisionedacyclic benzene ring extension strategy that would comprise the following steps (Scheme 2): (i)startingf luoroarenes would be subjected to formylalkylation via an S N Ar reaction to provide arylacetoaldehydes; (ii)the aldehydesw ould be then subjected to difluorovinylidenation; [8] finally,( iii)the Friedel-Crafts-typec yclizationo ft he obtained 1,1-difluoroallenes [9] would furnish the benzene ring-extended fluoroarenes.However,S N Ar reactions of fluoroarenes have been conducted on arenes activated by electron-withdrawing groups, including halogenes and trifluoromethyl groups, [12] and the S N Ar Scheme1.F-PAH Syntheses.Scheme2.Benzene ring extension cycle.[a] Dr.…”

Das Aufrollen von Oligophenylenen zu Nanographenen durch einen HF‐Reißverschluss

“…Dazu gehçren Halogenierung, [27,28] Borylierung [29,30] und Arylierung über eine Ullmann-Kreuzkupplung. Dazu gehçren Halogenierung, [27,28] Borylierung [29,30] und Arylierung über eine Ullmann-Kreuzkupplung.…”

“…Die ortho-Position zur aromatischen C-F-Bindung kann selektiv lithiiert werden, was eine einfache ortho-Funktionalisierung von Fluorarenen ermçglicht. Dazu gehçren Halogenierung, [27,28] Borylierung [29,30] und Arylierung über eine Ullmann-Kreuzkupplung. [31] Die Kombination einer Suzuki-Reaktion mit der metallorganischen Chemie von Fluorarenen bietet einen einfachen Zugang zu den endfunktionalisierten meta-Fluoroligophenylenen.…”

Alkynes as Linchpins for the Additive Annulation of Biphenyls: Convergent Construction of Functionalized Fused Helicenes

“…[14] An attractive metal-free approach to additive annulation of biphenyls would be to couple iodo-cyclization of alkynes with directed Mallory photocyclization of the o-terphenyl intermediate. [15,16] Thea dvantage of this approach is that the dearomatized dihydrophenanthrene intermediates derived from the iodo-substituted substrates can undergo irreversible rearomatization via simple elimination of HX under mild conditions.T he use of such "preoxidized" substrates with an electronegative substituent, X, on one of the reacting carbons at the ring closure point obviates the need for an external oxidant for the aromatization step.M ost of the effort has focused on X = Cl, [17] Br, [18] OMe [19] and more recently X = F [20] while surprisingly little is known about iodinated oterphenyls. [21] Undeterred by this scarcity,w ed ecided to explore the possibility of coupling iodocyclizations [22] to light-induced cyclodehydroiodination (CDHI).…”