Aza-Diels–Alder Approach to Diquinolineanthracene and Polydiquinolineanthracene Derivatives

Abstract

This study describes the synthesis of modular diquinolineanthracene and polydiquinolineanthracene derivatives. The reported facile and scalable aza-Diels-Alder-based approach requires mild conditions, proceeds in two steps, uses commercially available starting materials, and accommodates varying functionalities. Given the known utility of the acene and quinoline motifs, the synthesized molecules and polymers hold promise for organic electronics applications.

An aza-Diels–Alder route to quinoline-based unnatural amino acids and polypeptide surrogates

“…[35][36][37][38][39][40][41][42][43] We reacted Fmoc-protected 4-amino-(L)phenylalanine with 4-octylbenzaldehyde according to literature procedures, obtaining aldimine 1 in good yields of 79% that were comparable to those reported for analogous imines (Scheme 1). [35][36][37][38][39] We next reacted 1 with phenylacetylene under our standard Povarov conditions, forming Fmoc-protected unnatural amino acid 2a in reasonable yields of 46% that were slightly lower than those reported for analogous heterocycles (Scheme 1). [35][36][37][38][39] We then used a routine peptide chemistry protocol to remove the Fmoc group, obtaining deprotected unnatural amino acid 2b in good yields of 83% (Scheme 1).…”

“…[35][36][37][38][39] We next reacted 1 with phenylacetylene under our standard Povarov conditions, forming Fmoc-protected unnatural amino acid 2a in reasonable yields of 46% that were slightly lower than those reported for analogous heterocycles (Scheme 1). [35][36][37][38][39] We then used a routine peptide chemistry protocol to remove the Fmoc group, obtaining deprotected unnatural amino acid 2b in good yields of 83% (Scheme 1). 44,45 We conrmed the identities of 1, 2a, and 2b through a combination of 1 H nuclear magnetic resonance (NMR) spectroscopy, 13 C NMR spectroscopy, and matrix assisted laser desorption/ ionization (MALDI) mass spectrometry (Fig.…”

“…This approach entails (1) the synthesis of a 2,4,8-substituted quinoline monomer in 6 synthetic steps from 2-nitroaniline as the starting material and (2) the iterative deprotection/coupling of this building block on solid support to generate oligoamide foldamers. Thus, we envisioned an alternative strategy based on our prior efforts, [35][36][37][38][39][40][41] which is illustrated in Fig. 1B.…”

“…[35][36][37][38][39][40][41][42][43] For instance, we have demonstrated the synthesis of polymers with difficult-to-access architectures and/or connectivities, such as 4,6-linked polyquinolines, zigzag polyquinolines, polydiquinolineanthracenes, and crowded polybenzoquinolines. [35][36][37][38][39] We have moreover studied the likely conformations and spectroscopic characteristics of these polymers (while also making judicious comparisons to corresponding model compounds). [35][36][37][38][39] In addition, we have described the synthesis of both nitrogencontaining expanded acenes and nitrogen-doped graphene nanoribbons from quinoline-substituted precursors.…”

“…[35][36][37][38][39] We have moreover studied the likely conformations and spectroscopic characteristics of these polymers (while also making judicious comparisons to corresponding model compounds). [35][36][37][38][39] In addition, we have described the synthesis of both nitrogencontaining expanded acenes and nitrogen-doped graphene nanoribbons from quinoline-substituted precursors. 40,41 We have furthermore interrogated the electronic structures of the acenes and nanoribbons via computational, electrochemical, scanning probe microscopy, and/or spectroscopic techniques.…”