Shining Light on Cyclopentadienone–Norbornadiene Diels–Alder Adducts to Enable Photoinduced Click Chemistry with Cyclopentadiene

Abstract

A new Diels–Alder (DA)-based photopatterning platform is presented, which exploits the irreversible, light-induced decarbonylation and subsequent cleavage of cyclopentadienone–norbornadiene (CPD–NBD) adducts. A series of CPD–NBD adducts have been prepared and systematically studied toward the use in a polymeric material photopatterning platform. By incorporating an optimized CPD–NBD adduct into polymer networks, it is demonstrated that cyclopentadiene may be unveiled upon 365 nm irradiation and subsequently clicked to a variety of maleimides with spatial control under mild reaction conditions and with fast kinetics. Unlike currently available photoinduced Diels–Alder reactions that rely on trapping transient, photocaged dienes, this platform introduces a persistent, yet highly reactive diene after irradiation, enabling the use of photosensitive species such as cyanine dyes to be patterned. To highlight the potential use of this platform in a variety of material applications, we demonstrate two proof-of-concepts: patterned conjugation of multiple dyes into a polyacrylate network and preprogrammed ligation of streptavidin into poly­(ethylene glycol) hydrogels.

Click Chemistry Mediated by Photochemical Energy

“…This chemistry has enabled the synthesis of various bioconjugates, and novel molecular structures in spatiotemporal controlled way in diverse systems. [14,19,20] A number of light triggered click reactions have been developed over time and have been reported in the literature. In photo click reactions, light is used to activate a functional group into a reactive specie which quickly undergoes bond formation with another reacting species.…”

“…The combination of mild photochemical reactions with the click chemistry has generated a new class of light mediated click reactions, commonly known as photoclick reactions. This chemistry has enabled the synthesis of various bioconjugates, and novel molecular structures in spatiotemporal controlled way in diverse systems [14,19,20] …”

Generation of Cyclopentadiene for Diels–Alder Reactions by Visible‐Light Irradiation of Iron Sandwich Complexes

“… [1] However, handling of cyclopentadienes is often complicated because of their fast self‐dimerization, and therefore, a method for their controlled generation in situ is highly desirable. Usually, cyclopentadienes are generated by the retro‐ Diels–Alder reaction of various norbornene derivatives [2–5] . Herein, we propose an alternative approach based on the photochemical decomposition of the cyclopentadienyl iron complexes.…”

“…Usually, cyclopentadienes are generated by the retro-Diels -Alder reaction of various norbornene derivatives. [2][3][4][5] Herein, we propose an alternative approach based on the photochemical decomposition of the cyclopentadienyl iron complexes. It should be noted that free cyclopentadienes have been previously generated by UV-irradiation of the substituted manganese complexes (C 5 R 5 )Mn(CO) 3 .…”

Postpolymerization modification of a sulfonyl fluoride‐decorated polynorbornene using the sulfur‐fluoride exchange click reaction

“…The first reaction to be widely considered a “click reaction” was the copper‐catalyzed, azide/alkyne cycloaddition, 3 which remains the quintessential example. However, since its initial conception, the designation of click status has been bestowed upon numerous other transformations (whether or not it's fully justified 4 ) including: Diels–Alder reactions, 5 carbonyl condensations, 6 epoxide openings, 7 thiol‐X reactions, 8 and strain‐promoted, bioorthogonal 9 cycloadditions.…”